Arquivo de etiquetas: Limite de 2º C

The 2-Degree Carbon Budget III

What is the Global Emissions Reduction Pathway for the 2-Degree Limit?

So we just defined the global budget for C02 emissions that is consistent with what is our objective, the objective of limiting the temperature increase to less than 2-degree Celsius.

What we’re going to do in this chapter is we’re going to look at the shape of the emission reduction trajectory to reach what we said was necessary and that is to reach net zero emissions by the second half of the century.431

So what are the emission reductions that are necessary over time and what are the implications of doing that?

In 2010 the global greenhouse gases annual emissions reached 50 gigaton of C02 equivalent. So if we are to reach net zero emissions by the second half of the century, it means that global greenhouse gases emissions need to decrease not only very significantly, but very rapidly.

Given all the uncertainties we discussed at each and every step of the calculation of the global carbon budget, there are several possible global emission reduction trajectories that give a likely chance of staying within the 2-degree limit.432

Again, we’re defining likely here as a probability higher than two-thirds, higher than 66%. But in spite of these uncertainties we can come up with pretty good estimates and we can define the range of a portfolio of scenarios staying within this 2-degree limit. In these scenarios the global greenhouse gases emissions need to get down to 22 gigaton of C02 equivalent by 2050.

The full range is in between 18 to 25 gigaton. That’s the level we need to reach by 2050. Again, you need to compare that to where we are today, it’s 22 in 2050 compared to 50 today. By the year 2020, the global greenhouse gases emissions already need to be lower than today’s level. It means that we need to pick the global emissions even before 2020, because by 2020 they need to reach 44 gigaton of C02 equivalent.

The full range again is in between 38 to 47 gigaton. And by the year 2030, it’s important to look at that because it’s also the focus of the current negotiations on climate change. So on the run-up to Paris in December, 2015, the countries are preparing contributions emission reduction pledges to the year 2030, so it’s important that we have this metric to compare it to what they will pledge in the international negotiations. And so to state within the 2-degree limit the global greenhouse gases emissions in 2030 need to reach 35 gigaton of C02 equivalent, the full range being in between 32 to 42 gigaton. Here I was talking about greenhouse gases emissions overall. So all the greenhouse gases.433

But the focus here is going to be on C02 emissions from the burning of fossil fuels in industry. So what does it mean for these emissions in particular as we’ve said, I mean this is the largest source of emissions. And here too, of course given only uncertainties there are many possible C02 energy emission reduction pathways that give a likely chance of staying within the 2-degree limit.

But let’s pick two examples. The first is the representative concentration pathway, 2.6. It’s a complicated term but it’s a scenario that was developed by the Netherlands’ Environmental Agency and it’s the scenario that was discussed in the IPCC Fifth Assessment Report, Working Group One. And that’s the scenario among others, but that was the central scenario discussed that gives a likely chance of staying within the 2-degree limit. And it reaches approximately 12 gigaton of C02 energy only in 2050. So remember, that was 22 gigaton of C02 equivalent by 2050 for all greenhouse gases and here we’re talking about 12 gigaton of C02 energy only in 2050.434

If we want to compare the result of that particular scenario with another one, we can use the scenario from the International Energy Agency, its 2-degree scenario. Important precision here, the International Energy Agency scenario gives not a likely chance of staying within the 2-degree limit, but only a 50% chance of staying within the 2-degree limit. So the level of C02 energy emissions in 2050 is a bit higher than in the previous scenario. And in fact it’s 15 gigaton of C02 energy by 2050. This is what you can see on the graph with the two trajectories from 2010 to 2050 and you can see that the scenario from the International Energy Agency is a bit higher than the scenario, RCP2.6 that was discussed in the IPCC Fifth Assessment Report, in part because they do not give the same probability of staying within the 2-degree limit.435

So that’s what we should do if we were serious with the commitment we took, the commitment to limit the temperature increase below 2-degrees Celsius. So are we serious?

Are we doing what it takes to reach the objective? Unfortunately the answer is pretty simple and this is, no. We’re not on track and we’re not even close to being on track with this objective.

In Copenhagen in 2009 and then in Cancún in 2010, all the large greenhouse gases emitting countries, so that is the U.S., China, the European Union, India, Brazil, South Africa, Mexico, Canada, Russia, all of them, they took some quantitative emission reductions or limitations in the case of some countries, targets to 2020.

That was of course a major breakthrough in the history of international climate negotiations because before that, only the developed countries and not even all of them had quantified targets to reduce their emissions. And for the first time in 2009 and then in 2010, all the large emitters of greenhouse gases, whether they be developed countries or middle-income countries took a target to the year 2020.436

The problem though is that these targets are collectively, widely insufficient to put the world on the 2-degree path. Though there is an internal inconsistency in our climate change agreement because we have a global goal, the 2-degree limit, but then the countries emission reduction targets do not add up to this goal. By how much is the question?

Well if countries emissions reduction pledges were fully implemented, then the 2020 level of global greenhouse gases emissions would be in between 52 and 56 gigaton of C02 equivalent.

And you know that in order to stay within the 2-degree limit, it’s not 52 or 56 gigaton of C02 equivalent that we need, but 44. So there is a big difference in between these two numbers. There is by the way an uncertainty. I’m saying in between 52 and 56, because it was not always very clear what was the target pledged by the different countries. It was not always clear mainly for two reasons. The first is that some pledges were expressed, framed as deviation from business-as-usual emissions or as improvements in the carbon intensity of GDP. So the ratio in between the carbon emissions and the GDP.

But there is of course an uncertainty regarding business-as-usual emissions, or what Is the rate of future GDP growth. So it’s not easy to translate into an absolute level of emissions, pledges when they are made in such a way. The other reason is that some countries put forward in the Copenhagen and then Cancun agreements some emission reduction ranges. And not only a single number.437

The European Union for example pledged a 20% to 30% emission reduction targets in 2020 compared to their level in 1990. And it said, well I’m only going to move to the high end of the range, to the 30% if other countries do their fair share of the effort. In the meantime, China pledged a 40% to 45% improvement in the carbon intensity of GDP. And India, a 20% to 25% improvement, also in the carbon intensity of its GDP.

And it said, both countries said, well we’re only going to move to the high end of the range if the developed countries provide us with the means we need, the international financial and technological support we need to implement the intended climate change mitigation actions and measures. So that’s why there is an uncertainty and that’s why I’m not able to tell you, well as a result of the agreement we have, here is where would be the emissions in 2050…in 2020.438

It’s a bit more complicated than that. We have to play with ranges. But the point is, start anyway. And the point is that there is a very significant gap in emission reductions to have a likely chance of staying within the 2-degree limit. The gap in 2020 is in fact as high as 8 to 12 gigaton of C02 equivalent.

This is a huge number, this is not only a margin of error, this is a very significant gap in emission reductions to again, just stick to the commitment we made. In particular, when you compare this gap with what the emission reduction pledges that have been made by countries would deliver, because they would in fact only deliver is 3 to 7 gigaton reduction compared to business-as-usual.

So the gap is even higher than what the pledges achieve compared to the continuation of the current trends. There is a very simple calculation that we can do and let’s do it together to give us an idea of the order of magnitude that is necessary to stay within the 2-degree limit. As we’ve said, today’s level of C02 energy emissions globally is approximately 32 gigaton of emissions.

If we use the International Energy Agency 2-degree scenario as a reference and again, that gives only a 50% chance of staying within the 2-degree limit, it means that the global C02 energy emissions need to be divided by a bit more than 2, by 2050, since they need to reach 15 gigaton of C02 energy by 2050. But in the meantime, according to the U.N. Population Division, Medium Fertility Forecasts the world population is expected to grow by 2050. In fact it’s expected to grow by 35% in the next 40 years, from approximately 7 billion people on the planet today to a bit more than 9.5 billion in 2050.

So if we divide the two numbers, it means that the global average per capita emissions need to be divided by 65% by 2050. Needs to go from 4.6 today to 1.6 tons of C02 energy emissions per person and per year in 2050. Why is it important to make this calculation? It’s important because it’s a pretty uncomfortable truth, but all countries will need to converge close to this global average of 1.6 tons of C02 energy per capita by 2050. Not that many countries will be able to have emissions higher than this level.

And this is the result of a simple mathematical calculation, because on the one hand, very few countries with C02 energy per capita higher than 1.6 tons today will simply technically be able to go far below this level by 2050, because that would push the boundaries of what is technically feasible. But on the other hand, the catch-up economic growth in the low income countries that currently emit less than 1.6 tons per head will increase their per capita emissions by 2050, or at least one should hope that growth in these countries has this effect, because it would be very good news for them.

And that would be the case even if they decrease the carbon intensity of their economic growth. So the truth is that if nobody can be far below or above the global average, then all countries should converge close to this average by 2050. It doesn’t mean that the convergence of per capita emissions is a way to allocate equitably the global carbon budget in between different countries.

And we’re going to come back to that in the next lectures, because it doesn’t take into account very important elements that are central to the equity of the global effort to reduce greenhouse gases emissions. In particular, it doesn’t account for the fact as we discussed previously that the historic contribution of the different countries is not the same.

So the developed countries have emitted much more so far than the developing countries. But it’s a simple mathematical conclusion that almost all countries will need to converge at least close to this level of 1.6 tons of C02 energy per capita by 2050.

The 2-Degree Carbon Budget II

What is the Global Carbon Budget for the 2-Degree Limit?

We just defined a very important concept, the notion of a global carbon budget. I admit this is a pretty complex and sophisticated notion, but I promise we’re going to make good use of it. And we’re going to do that right away.

We’re going to apply the concepts to what is of interest to us of course and that is the global carbon budget for the 2-degree limit, because this is our objective. This is what we need to do to avoid dangerous climate change.421

So how do we calculate this budget? Well we need to look at the greenhouse gases concentration that is consistent with this objective.

So we said it was in between 430 and 480 parts per million of CO2 equivalent. And what is especially important is to calculate the global budget for CO2 emissions only, because as we’ve said repeatedly, CO2 is the single largest source of total greenhouse gases emissions. And it…also because it remains in the atmosphere much longer than most of the other greenhouse gases and in particular methane.

So we’re trying to narrow down the issue a little bit and to calculate a global carbon budget for CO2 only as opposed to all greenhouse gases. So in order to do that, to limit the analysis to CO2, we need to be making a number of assumptions. First, regarding the known CO2 greenhouse gases emissions like methane, nitrous oxide, or fluorinated gases. Second, we need to make assumptions regarding the contribution from other climate changing factors such as the aerosols and land use albedo.

Jeffrey Sachs explained in detail in some of the previous lectures on where the impacts of these factors. Third, we need to make an assumption regarding the timing of CO2 emission reductions and therefore the time the carbon cycle has to absorb the CO2 that is emitted. And fourth and finally, we have to make assumptions regarding the sensitivity of the climate to CO2 emissions and these other climate forcing.

So it’s, it’s a comprehensive set of assumptions we need to be making. There are uncertainties in climate science at each and every step of these assumptions. But taking into account all these factors, the global budget for CO2 emissions to the end of the century to stay within the 2-degree limit is within the range of 630 and 1180 billion tons of CO2, or gigatons.

That’s the budget for CO2 to the end of the century. What is also very important is to calculate this global budget for CO2 emissions to stay within the 2-degree limit, not only to the period to the end of the century, but only to mid-century, to the year 2050, because I guess you will agree with me that the end of the century, although I hope we’ve shown you that it is very relevant from a climate science perspective is of course very far from an economic perspective or even worse, from a political standpoint.

422Countries’ long-term emission reduction objectives, when they have one and the problem in fact is that not that many of them have one so far, but we’re going to be discussing in the, in the next lectures why they should have one and what it should be. Countries’ emission reduction objectives are to the best to the year 2050 and not to the end of the century. So it is very important that we’re able to calculate a global budget to 2050 because we need to be able to calculate, to assess if countries’ projected cumulative emissions to 2050 collectively fit within the global budget to stay within the 2-degree limit, because we need to be able to assess if the emission reduction targets that are taken by the different countries add up and are sufficient to reach the global goal.

So if we’re trying to define a budget to mid-century as opposed to, to the end of the century, we need to very simply take the century long CO2 emissions and divide them into two time periods, to mid-century first and then from 2050 to the end of the century. And of course the bulk of emissions will occur during the first period to the year 2050 because to stabilize greenhouse gases concentrations the net emissions should decline to zero during the second period.

But here I want to mention something very important and that is that some scenarios, not all of them but a significant fraction of them are based on the idea of net negative emissions during the second half of the century. What is it? What, what does net negative emissions mean?

How could emissions be net negative, so below zero? Well there is a number of different potential technologies that could be used to achieve net negative emissions. In particular, it could be achieved if the use of biomass for energy production was deployed in combination with carbon capture and sequestration. So it means that the biomass would be burned in the power plants and then the power plants would in turn capture and sequester the CO2 that is emitted.423

This is what we call bio-energy plus carbon capture and sequestration. And this is only one out of several potential net negative emissions technology, including the direct air capture of CO2. So to the extents that negative emissions are available on a large-scale in the second half of the century, the budget for CO2 emissions for the first half of the century would be of course correspondingly higher.

But there is an important but here. The feasibility and the sustainability of the large-scale deployment of net negative emissions technology is still very much under debate. I mean not impossible and we should do everything that’s possible to make it a future reality, but still unproven at this stage. In particular, what I just mentioned bio-energy plus carbon capture and sequestration raises very serious issues, because it combines the twin challenges of large-scale biomass production on the one side and the large-scale storage of CO2 on the other hand.

And at the global level, the large-scale use of biomass for energy production could cause deforestation or compete with land use for other purposes such as food production for example, which would have a very negative effect on food security. This is not to say that it cannot be done. In particular in some countries and under some specific circumstances with new generations of biofuels it could be done in a sustainable manner, but we’ve got to be very careful about the way we do it. And it isn’t clear what is the scale of the potential for doing it in a sustainable manner without contributing to deforestation or without competing with land use for food purposes.

That’s one. On the other end the scale of the geological potential for a CO2 sequestration is also very much under debate.

We’re going to be discussing in some of the next lectures that CCS is a well-known technology. I mean it’s not as if we had no clue how to do it. Each and every element of CCS capture and sequestration and transport is a known technology, but it’s unclear what is the geological potential to sequestrate in a safe manner this CO2 under the ground. And what’s more, even if CCS became a reality, it would have to be deployed first on fossil fuel power plants and industry and not first on bio-energy plants. So that being said, if we exclude at least for the time being the option for a net negative emissions, again that seems to be prudent at this stage of research and development given the uncertainty regarding their feasibility and their sustainability.

If we exclude the option for a net negative emissions, then the global budget for CO2 emissions to mid-century, to the year 2050 is of 825 gigaton, or billion tons. And it is of 950 gigaton to the end of the century, which simple calculation here would imply a 125 gigaton of cumulative emissions during the second half of the century, starting the year 2050 to the end of the century.424

That being said, it is very important that we scale up the support for research programs that would explore the feasibility and the sustainability of net negative emission technology options such as bio-energy plus carbon capture and sequestration, or direct air capture of CO2 emissions, because it would increase the size of the carbon budget that we can use when the carbon budget is very tough and very strict. So, so far we have calculated a global budget to stay within the 2 degree limit for CO2 emissions, but we’ve combined CO2 emissions from very different sources in fact. I mean from the burning of fossil fuels and industrial processes, but also from land use. So the emissions coming from deforestation or the emissions coming from agriculture.

If we want to define a global budget for CO2 coming only from the burning of fossil fuels and industrial processes, then we need to make yet another assumption. We need to make an assumption regarding the potential for CO2 emission reductions in the land use sector, but also for the potential net biological sequestration of CO2, because it’s possible to achieve net biological sequestration through different types of practices such as reforestation or peat production or wetland restoration, or even improved agricultural practices.

The assumption that is the most often made in the scientific literature is the assumption of net zero emissions from land use over the century. So if that is the case, it means that the 950 gigaton global budget for total CO2 emissions we defined by the end of this century to stay within the 2-degree limit can be considered as a budget for CO2 energy only. But here again I want to stress that there is great uncertainty regarding the precise potential but also the timing for possible CO2 emission reductions and net biological sequestration of CO2 in land use.

I mean it might well prove impossible to achieve net zero emissions in the land use sector which would be bad news because it would further reduce the size of the budget for CO2 energy. So it would reduce the emissions that can come from energy production, transformation and consumption. But on the other hand it, it may well prove possible to achieve net negative emissions in advance of the end of the century in which case, the global budget for CO2 energy would be higher which would be a, a good news. S

o far, the answer is, given the state of the research that we don’t really know, so it’s really urgent that we do more research to see and define more clearly the budget for CO2 energy. But as a first approximation, I mean we can use what we calculated and that is 950 gigaton of CO2 energy emissions by the end of the century in total to stay within the 2-degree limit.

The 2-Degree Carbon Budget I

What is a Carbon Budget?

In the previous lectures we have discussed why limiting the temperature increase below 2-degrees Celsius compared to the pre-industrial levels was so important. We’ve seen of course why it is so important from an environmental point of view to protect the planet, but we’ve also seen why it was so important from an economic and and social perspective, because the impacts of climate change, of uncontrolled climate change, would really be catastrophic and would even threaten our basic ability for example to eradicate poverty.

Today we’re going to continue in our journey to see how we can avoid these catastrophic impacts and how the world can meet the challenge of what we’ve called the deep decarbonization in the sense removing the carbon from our economy and in particular from our energy systems. We’re going to see in particular, what is the level of emission that is consistent with this 2-degree limit over time.344

So this first chapter really is about a key concept, is answering this question. The question is how much anthropogenic greenhouse gases emissions, so again, the emissions resulting from our human activities, our energy production transformation and consumption processes, the emissions from our industrial activities, cement, steel, aluminum production, et cetera.

And the emissions also from land: land use change, from agriculture or from deforestation. How much of these anthropogenic greenhouse gases emissions can we still emit if we want to have a chance to live within the limit we’ve set, the 2-degree limit?

The key concept we’re going to be using to answer this essential question is the concept of the carbon budget. So I’ll explain in further detail what I mean by that, but in, in simple terms a carbon budget is defined as the maximum level of cumulative that is over time as opposed to just emissions a given year.

So a carbon budget is defined as the maximum level of cumulative emissions to stay within a degree of temperature increase. So how do we calculate this budget? Well as we’ve said repeatedly now, there are four main greenhouse gases: carbon dioxide, methane, nitrous oxide, and the fluorinated gases.411

What is important when trying to estimate a carbon budget is to know that these different greenhouse gases remain in the atmosphere for different amounts of times. Very different in fact, amounts of time, from several months for some to millennium for some others. So they affect the climate on very different time scales. The lifetime in the atmosphere of CO2 in particular, the single largest source of greenhouse gases is unfortunately for us the most difficult to determine because there are several different processes that remove C02 from the atmosphere.

First, in between 65% and 80% of CO2 that is released in the atmosphere dissolves into the ocean over a period of somewhere in between 20 to 200 years. The rest of CO2 that’s not dissolved into the ocean is removed by other processes, but by processes that take up to several hundreds of thousands of years to happen.412

That means that once in the atmosphere, the CO2 can continue to affect the climate for hundreds of thousands of years. Methane, by contrast, CH4, is mostly removed from the atmosphere by chemical reaction. And this is a much faster process which takes about 12 years to complete. So overall, since greenhouse gases emissions and in particular, CO2 stay in the atmosphere for a very long period of time after they have been emitted, it is the cumulative level of greenhouse gases emissions that has an impact on the climate and not the emissions at a particular point in time.

That’s why we’re going to be using the notion, the concept of a carbon budget to look at the cumulative level of emissions over time. So what is the relation here in between greenhouse gases emissions and the temperature increase?

Well there is a meaningful correlation in between three things. The first is the level of cumulative greenhouse gases emissions, which we measure in tons of CO2 equivalent. Again, CO2 equivalent to measure with one unit and all the greenhouse gases are not only CO2, because they will have a warming potential.413

Second, their long-term concentration and their radiative forcings which we measure in parts per million of CO2 equivalent and in watts per square meter, so watts per surface, respectively.

And third, the resulting mean surface temperature response which we measure very simply in increases in global average and temperature. The relation in between the cumulative greenhouse gases emissions and the global temperature response is approximately linear.

So for any degree of temperature increase, and let me remind you that we’re interested in one in particular, the 2-degree limit, it is possible to determine the corresponding maximum level of cumulative greenhouse gases emissions. And this is what we call the global carbon budget.

That being said, there is an uncertainty surrounding the relationship of cumulative greenhouse gases emissions and the resulting global temperature increase. So since there is such an uncertainty, we must speak in terms of probability. A given cumulative path of greenhouse gases emissions will only yield for a given probability of staying below an increase of let’s say 2-degree Celsius of global warming.414

In general we are interested in greenhouse gases emission pathways that give a likely chance of staying within the 2-degree limit and not only a very small probability because that wouldn’t be that interesting to know that it offers only a 5% chance of reaching the objective. Usually, we define likely to try to give it a quantitative meaning, we define likely as a probability of two-thirds or higher. So higher than 66% chances of staying within a certain degree of warming.

Science tells us that to have a likely chance of staying within the 2 degree limit, again, defined as a probability higher than two-thirds, the greenhouse gases concentration must stabilize at somewhere in between 430 and 480 parts per million of CO2 equivalent. This is an important number for you to remember because it gives the equivalent concentration of greenhouse gases to the 2-degree limit.411

The 2-Degree Limit IV

Debates Over the 2-Degree Celsius Limit

So we’ve just looked at the history of how the 2-degree limit in the mean surface temperature increase compared to pre-industrial level became the politically agreed, but also the legal objective of global climate change mitigation as a result of an interesting scientific but also political process through the negotiations. Even though that is the politically agreed goal and even though almost all countries are part and parties to the U.N. Convention on Climate Change, it does not mean that everybody agrees with the 2-degree limit. There is in fact a pretty hot debate as to whether this is the right objective for our mitigation efforts. And there are really two sides to the arguments.


So we’re going to try to make sense of these different arguments. On the one side, some leading climate scientists and in particular Professor Jim Hansen we’ve already mentioned quite a few times in these lectures, argue that even a mean surface temperature increase limited to 2-degrees Celsius could be catastrophic. And they instead argue that we should be aiming for a 1-degree Celsius target instead of the 2-degree Celsius target. So that’s one side of the argument. In the meantime some observers claim that staying within the 2-degree limit is way too difficult, but also way too costly if that proved feasible. And therefore, they claim that the 2-degree limit should be either weakened.

I mean we should try to adopt an easier and less costly target or some even go as far as saying that it should be simply dropped and that the world should follow a bottom up approach to climate change mitigation and that after all, countries or businesses should only do what they can do and what they want to do. So that’s the two sides of the arguments. And you can see that the 2-degree limit is pretty much under fire, but does it really mean that the 2-degree limit should be revised?

The problem is that it would be difficult just by looking at these arguments to decide if it should be revised upward or downward. So let’s look in further details at the arguments of both sides to try to make sense of them.

On the one hand, it is completely true that the recent scientific evidence suggests that global warming of 2-degrees Celsius may well generate very severe and irreversible risks. Again, this is why some leading climate scientists are advising for a 1-degree Celsius target instead. What are their arguments, really? Well they point out to the earth’s paleoclimate history. And they say that it, it points to the fact that 2-degrees Celsius of global warming is likely to result in sea level rise of 6 meters in the long-run, which I guess everybody would agree is an extremely significant threat. And it’s very difficult to see how most of the places could barely adapt to such a rise in the level of the sea.

Another argument they have is that they emphasize that global warming of 2-degrees Celsius could induce what they call slope amplifying feedbacks. Another way to call it is to call that chain effects from climate change.

So let’s look very simply at two examples. The first is that the Amazon forests could eventually die off as a result of repeated drought. And this is a very serious potential problem because the Amazon forest is a major sink of carbon emissions. So the die-off of the Amazon forest would increase and release massive amounts of C02 in the atmosphere and that would in turn further aggravate climate change.342

Another example is that the methane and the carbon dioxide currently buried into the permafrost of the tundra could also be released into the air as the tundra melts as a result of global warming. So that’s another example of amplifying feedback and chain effects of climate change.

So it’s true that by pushing the climate beyond the experience of the human era for the past 100,000 years, we risk inducing conditions that are inhospitable for the human species and millions of others by the way. So it’s very important to understand that a 2-degree increase in temperature is far from being risk free. This is not what it is about. But keeping below 2-degrees Celsius of global warming is really absolutely essential to maintain climate change within the boundaries of manageable risks and simply to maintain our ability to adapt to the effects of climate change.

So that was one side of the argument. On the other side, some observers claim that as I already said, staying within the 2-degree limit is too difficult and too costly. Here really the recent scientific evidence does not support this claim. It indicates that keeping below the 2-degree limit for sure is extremely challenging. I mean we’re not arguing here that this is an easy task. But it points to the fact that this is feasible even assuming business as usual, economic growth and development.

There are many global studies, many authoritative global  studies making the same point, including the scenarios reviewed by the IPCC recently released Fifth Assessment Report. But also the publications by the International Energy Agency, the IEA, or the Global Energy Assessment led by the Institute of Applied Systems analysis. All these studies, all these authoritative, serious studies show that reducing global greenhouse gases emissions to a level that is consistent with the 2-degree limit is still within reach, using technologies that are either already commercially available, or demonstrated at the pilot scale.

Even if, and it’s very important to recognize that they would need further research and development to be deployed at the scale that is needed to achieve the deep decarbonization of the energy systems. And we’re going to dedicate one full lecture to discuss the necessary research and development that is necessary to bring these technologies to eventually large-scale deployment. But what these studies also show very clearly is that the window of opportunity to stay, to keep the 2-degree limit within reach is closing very fast. So it, it’s certainly true that countries need to act very quickly and in a very determined and, and also coordinated manner to keep that target within reach, if we don’t want it to simply disappear.

343The question is what would be the cost of reducing greenhouse gases emissions to a level that is consistent with this 2-degree limit? And how does it compare to two things really, one, how does it compare to the size of the global economy? It’s important to look at that, to see if we have the ability to invest into climate change mitigation actions.

But also very importantly, we need to compare the cost of mitigating climate change that is reducing greenhouse gases emissions to the cost of climate change itself because it’s based on this comparison that we should take a decision as to what is the appropriate level of climate change that we can afford and what is the level of climate change we should not exceed because it would induce very high costs. The modeling of the overall impact of climate change in monetary terms, that is if we try to quantify using U.S. dollars for example is a formidable challenge.

And it is very important to recognize the limitations to modeling the world over one century or more. And that clearly demands that we have great caution in interpreting the results coming from these modeling scenarios. That would be very convenient if we didn’t have to use these models, but the problem is that we do. We do, because of the basic nature of the challenge. Because when it comes to climate change, the lags from action to the effect are very long. So the quantitative analysis we need to do because we need to inform policy decisions by quantitative analysis is dependent on these long-range modeling exercises as George Box once very famously said, and there is a lot of truth in that statement, “all models are wrong, but some are useful.”

So we’re going to be using these models with caution, but this is very important that we look at what they have to say to inform our decisions. So what do they teach us? Well with global warming exceeding 4-degrees Celsius, existing models that include the risk of abrupt and large-scale climate change estimates an average 5% to 10% loss in global GDP, the gross domestic product, with poor countries suffering the most in costs in excess of 10% of their GDP.

But there are some limitations as I said to these models. And what we know is that the cost of business-as-usual, so the cost of the continuation of the current trends if we do nothing to control climate change would increase still further if the model were able to take into account more systematically two very important factors which most of the time they fail to do.

The first is if they included the direct impacts on the environment and human health, which sometimes we call the non-market impacts, because they’re difficult to quantify in monetary terms.

And the, the second element is that recent scientific evidence indicates that the climate system may be more responsive to greenhouse gases emissions than we previously thought.

This is what we just discussed, that there might be slope amplifying feedbacks and chain effects that release further carbon dioxide and methane as a result of global warming itself. So if we put these two elements and build them into the modeling framework, then they would increase the total cost of uncontrolled climate change, of business-as-usual climate change to the equivalent of 20% of reduction in consumption per head now and into the future.

344So it is very important to understand that the assessment modeling of the cost of climate change impacts has to be built around the economics of risk and not only the traditional cost-benefit analysis. Because averaging across possibilities conceals the risks. And the risks of outcomes much worse than expected are very real and they could be catastrophic as we have been discussing in the previous chapters. So by nature, climate mitigation policy is about reducing these risks. It’s true that they cannot be completely eliminated, but they can be substantially reduced and this is what we should be aiming for in real life.

So a climate change modeling framework also has to take into account ethical judgment on the distribution of income and how to treat future generations. And it should not focus on narrow measures of income like GDP because as we’ve said, the consequences of climate change for health and for the environment are likely to be severe, but are difficult to reflect into a narrow indicator like GDP. So all these principles need to inform the way we do the cost calculation of the impacts of climate change, but also of climate change mitigation measures.

Turning to the estimations of the costs of climate change mitigation. It can basically be done in two ways and both of them are complimentary and we’re going to be using both of them.

One is rather simply to look at the resource costs of measures, including the introduction of low common technologies and other changes that are necessary such as changes in land use. And to compare the cost of these measures with the costs of the business-as-usual alternatives. So what would happen if we didn’t invest in climate change mitigation?

Another type of analysis more complex but also very useful is to use macroeconomic models to explore the system-wide effects of the transition to a low common economy. It can be very useful in tracking the dynamic interactions of the different factors over time, including the response of the economies to the changes in relative prices. That can be complex for sure, with their results affected by a whole range of assumptions, but they still provide very useful insights.

On the basis of these two methods, so the bottom-up technological analysis and the more sophisticated macroeconomic analysis, the central estimate is that the stabilization of greenhouse gases emissions at level of 500 to 550 parts per million of C02 equivalent will cost on average around 1% of annual global GDP by 2050. The results of the bottom-up technology modeling range from minus 1%, so even in that gain compared to the business-as-usual, to plus 3.5%. So a net cost of GDP and the results of a top-down macroeconomic modeling range from minus 2%, so again, a net gain to plus 5%, a net cost of GDP. This is significant for sure. This is not a marginal cost, but this has to be looked at as an investment cost and not as a pure loss. And this is fully consistent with continued growth and development. In contrast by the way with uncontrolled business-as-usual climate change, which will eventually pose very significant threat to growth and development.

So let’s try to conclude by summarizing everything we’ve learned in this lecture. The first point that’s going to guide the rest of our journey and further exploration of how we meet the challenge of deep decarbonization is that 2-degrees Celsius is really the upper limit for climate safety, because beyond 2-degrees Celsius of global warming, it is our basic ability to adapt to the likely impact of climate change that is at risk. Second, staying within the 2-degree limit is technically feasible and the costs are relatively modest compared to the size of the global economy, that’s one. But also and very importantly, compared to the cost of the potential impacts from climate change itself. So there is a very good economic case  to be made for climate change mitigation. The conclusion is that the 2-degree limit is a very important tool that we have that must be preserved, but also that must be operationalized in the agreement we’re trying to reach in 2015 in Paris, because only an internationally coordinated, goal oriented, it’s very important, approach to climate change mitigation will allow us to be on track and avoid dangerous climate change. The truth is, unfortunately, that very few countries have looked seriously at the implications for them of staying within the 2-degree limit. So that’s why in the next lectures we will explore in detail, but also country by country the deep transformation of the global economy and in particular, of the energy systems that are required to stay within the 2-degree limit.

The 2-Degree Limit III

Limiting the Mean Surface Temperature Increase Below 2-Degrees Celsius vs. Pre-Industrial Levels

So, we just discussed what would be the absolutely catastrophic consequences of climate change if we did nothing to control the rising greenhouse gases emissions.

Now, I want us to spend some time discussing what we could do to avoid these catastrophic consequences and in particular at what level we should try to limit the increase in temperature.331

So as we have already been discussing in 2010, during the Sixteenth Conference of the Parties of the United Nations Framework Convention on Climate Change. The world’s governments gathered and decided for the first time that they would operationalize the ultimate objective of the UNFCCC which so far remained a bit vague and they decided to set a particular quantitative target of limiting the increase in mean surface temperature below 2 degrees Celsius compared to preindustrial levels. Of course this in recognition of the extreme risks for a safety of the planet but also for a future development opportunity of the temperature increase exceeding two degrees Celsius as we just discussed by looking at some of the potential impacts but what is really interesting and what I want us to spend a little bit of time discussing is that the adoption of this particular target was really the result of of a long and complex process.332

It was very interestingly the result both of a scientific but also of a political process. A scientific process first because each assessment report of the Intergovernmental Panel on Climate Change, the IPCC, provided new insights on three things. I mean the IPCC is divided into 3 main working groups: the first is on the basics of climate science, the second is on the risks of climate change and how we can adapt to them, and the third working group is on the opportunities for climate change mitigation on the economics and the policies of climate change mitigation, so each assessment report of the IPCC provided not only by the way more precise estimates but also revised estimates and in general and we’re gonna go through the history of these different assessment reports in general sending each and every time an even more alarming message to the world than the previous reports.

But I said that it was not only the result of the scientific process but also the political process and it’s very important to understand that the two-degree limit is really the result of the combination of science but also politics because some countries or groups of countries and in particular the European Union or the small islands developing states really pushed hard in the negotiations for the adoption of a particular long-term goal to climate change mitigation.333

So let’s look in detail at the key milestone334s in this scientific but also political process. It all began in a way in 1989 when an advisory group to the United Nations Environment Programme or UNEP released what really became a landmark report. One of the key conclusions of this report was that an increase in the mean surface temperature of 2 degrees Celsius is and I quote “An upper limit beyond which the risks of grave damage to ecosystems and of nonlinear responses are expected to increase rapidly.” So that’s one of the very first mention of the 2 degree limit in an official document commissioned by the United Nations Environment Program. One-year later in 1990 the Second World Climate Conference was a very important step towards adopting a global climate change treaty.

The conference was sponsored by The World Meteorological Organization and also by UNEP, and this time it aimed at making very concrete policy recommendations on the run up to the negotiation of the climate  treaty, and one of these recommendations was that the ultimate objective should be to stabilize greenhouse gases concentration at a level that would prevent dangerous anthropogenic interference with the climate system. It should sound very familiar because as we have discussed several times.

Now two years later in 1992 the United Nations Framework Convention on Climate Change was adopted, and its ultimate objective is directly in line with the recommendation coming from The World Climate Conference. So moving on, in 1995 the IPCC released its Second Assessment Report, and it was also a very important report. It looked at the consequences of the doubling of the greenhouse gases concentrations of the time to a level of 550 parts-per-million of CO2 equivalent, and here one-year later in 1996 enters the European Union which played a very instrumental role in having the two-degree limit adopted as the global goal of climate change mitigation because in 1996 the European Union Environment Council picked up the conclusion from the IPCC Second Assessment Report, and it said the European Union Environment Council that it believed that global average temperature increase should not exceed two degrees Celsius above pre-industrial levels and therefore that the concentration levels of greenhouse gases lower than 550 parts-per-million CO2 equivalent should guide the global greenhouse gases limitation and reduction efforts.335

This is in fact the very first time that the two-degree limit is picked up politically as opposed to only in a scientific report but what is also interesting is to look at the concentration of greenhouse gases that was at that point in time associated with the two  degree limit because again at that point in time we are going to  see that after that, science made progress, but at that point in time it was considered that stabilizing greenhouse gases concentrations at 550 parts-per-million would be sufficient to limit the increase in temperature below 2 degrees Celsius.

After that came the Third Assessment Report of the IPCC in 2001, and it revised and it revised pretty significantly  the analysis included in the Second Assessment Report, and in many ways the conclusions of the Third Assessment Report were more pessimistic and the message that was sent was even more alarming. In particular, the projected increase in temperature over the next century had increased from a range of 1 to 3.5 degrees Celsius in the Second Assessment Report to 1.4 to 5.8 degrees Celsius in the Third Assessment Report.336

Again, the European Union was key in the process and in 2005 it organized a Heads of State Summit this time and not only a meeting of the Environment Ministers. It organized The Heads of State Summit to discuss the issue of climate change and to define the European Union position in the upcoming international negotiations, and it concluded that and I quote, “With a view to achieving the ultimate objective of the UNFCCC, the global average surface temperature increase should not exceed 2 degrees Celsius above pre-industrial levels but what is really interesting and what I want you to focus on is that the European Union Environment Council added that based on the recent scientific research from the IPCC it became unlikely that the stabilization of concentrations above 550 parts-per-million of CO2 equivalent would be consistent with staying within the two-degree limit and that in order to have a reasonable change of limiting global warming to no more than 2 degrees Celsius then the stabilization of greenhouse gases concentrations well below 550 parts-per-million of CO2 equivalent may be needed.337

Two years after that in 2007 the IPCC released another this time The Fourth Assessment Report, and it concluded that in order to limit the temperature increase below 2 degrees Celsius, the concentration of greenhouse gases emissions would have to be stabilized below 450 parts per million instead of the 550 parts-per-million as was previously sought. Following the publication of the IPCC Fourth Assessment Report, the European Union Environment Council concluded that the IPCC Fourth Assessment Report demonstrates that keeping the two-degree objective within reach requires the stabilization of the concentration of greenhouse gases emissions in the atmosphere in line with the lowest stabilization level that was assessed in the report and that was 450 ppm of CO2 equivalent, but interestingly, and I want to emphasize this part compared to the previous assessment reports.

The Fourth Assessment Report did not only revise its analysis of the temperature response of the planet to greenhouse gases concentrations it also revised its analysis of the risks induced by global warming of 2 degrees Celsius and some of the risks that were previously estimated to be only limited became this time assessed as severe or even very severe but in spite of this new assessment of the risks induced by even only two degree of global warming, the political support for the two-degree limit grew and many other countries such as Chile or New Zealand or Norway or South Africa or Switzerland to quote only a few of the much larger number rallied the European Union position to make the two-degree limit the long-term goal of global climate change mitigation  efforts.338

It is very important to stress that not everybody agreed with that particular objective and in particular the small islands developing states were arguing for a 1.5 degree Celsius limit or to put it in concentration equivalent–a 350 parts-per-million concentration of greenhouse gases—because they were pointing and very rightly so to the risks to their very survival of global warming of 2 degrees Celsius because in particular of the rise in sea levels we discussed that would result from that, but even though not everybody agreed to 2 as opposed to 1.5 degrees Celsius, the Copenhagen Accord was adopted in 2009 as a political declaration and then put back into the legal framework of the UN Convention on Climate Change in 2010 and this is really the first time that within the legally-binding instrument internationally there is not only a recognition that the two-degree limit should guide the global mitigation efforts but also the recognition of the need to consider the strengthening of the long-term global goal in particular maybe to 1.5 degrees Celsius.

339So this is the history of the process as you can see; inputs from science but also in the end the very political decision to make the two-degree limit the long-term global goal of mitigation effort. here is to be frank some irony one might put it like that in the fact that as we’ve seen as new scientific evidence became available the temperature increase resulting from a given concentration tended to be higher than previously thought and so tended to be the impacts resulting from a given temperature increase in particular 2 degrees Celsius so in fact 2 degrees Celsius has long been in the thoughts of people as the objective but it somehow changed meaning as scientific evidence progressed because the impacts attached to that particular target were considered to be even more significant than previously thought but in the meantime global greenhouse gases emissions continue to increase and at an always faster rate and the window of opportunity to stay within the two-degree limit closes very rapidly which is a very big problem because as we’ve seen two-degrees is really the upper limit for safety so we’re gonna try to see what we can do to keep that target within reach.

The 2-Degree Limit II

The Consequences of the BAU Trajectory

So we’re going to be discussing the consequences of what I just described, so the consequences of these rising greenhouse gases emissions, of the rising concentration, and of the resulting temperature increase.

The truth is that, in short but we’re going to go in further detail in a minute, that global warming of 4 degrees Celsius or more would have very severe and irreversible impacts and the truth is that these impacts would really threaten the continuation of economic development in the future and also to be frank threaten our ability to adapt to these impacts if global warming were to even exceed 4 degree Celsius so in the previous lectures we’ve already looked at some of the examples in many countries of climate change that is already occurring and and some of these impacts but now we’re gonna look a bit more systematically and also a bit more theoretically at some of the most important risks of climate change going forward and in particular we’re going to discuss three among these most important risks.322

One being the rise in sea levels associated with global warming, the other being the acidification of oceans as the concentration of CO2 increases in the atmosphere since the oceans trap part of this increase in concentration, and the third and again we’ve already looked at evidence of them happening, is the increased frequency and also the increased intensity of extreme weather events such as heat waves and or floods.

So let’s look first at the rise of sea level. How can the increase in CO2 concentration result in a rise of the see. Well, the mechanism is pretty complex but if we try to simplify it, the rise in the level of the sea is caused by the thermal expansion of the oceans but also by the addition of water to the oceans as a result of two things: the melting and the discharge of ice from mountain glaciers but also ice caps and from the much larger Greenland and Antarctic ice sheets.

So let’s try to quantify a little bit the rise in sea levels that would result from global warming. The estimate is that global warming of 4 degrees Celsius would lead to a sea level rise of approximately 0.5 to 1 meters possibly more according to some estimates by the end of the century. But there is something very important you need to understand here and it is that the rise in sea levels is a very slow process that would continue long after the concentration of greenhouse gases emissions has stabilized so if greenhouse gases emissions led to 4 degrees Celsius of global warming, the rise in sea levels would not stop at 0.5 or 1 meter by the end of the century.

It would be several meters higher in the coming centuries adding to the risks induced by global warming. Even if greenhouse gases emissions were reduced in order to limit global warming to only 2 degrees Celsius the sea level rise would be about 0.3 to 0.8 meters by the end of the century but again and let me stress that it wouldn’t stop by the end of the century and it would continue to rise after and most estimates range in between 1.5 and 4 meters of sea level rise by the year 2300 and I should also point out that some estimates and not funny estimates but really really serious estimates even forecast a 6 meter rise in the sea level in the long run associated with a two-degree only of global warming.

The truth is that the sea level rise would likely be limited to below 2 meters in the long run only if global warming was kept to well below 1.5 degree Celsius, maybe something like 1 degree Celsius so why is it a problem It is pretty obvious that such an increase such a rise in the sea level would have really harmful consequences in particular because a very significant fraction of the world population is settled along the coastlines and and often in in large cities so a sea-level rise that would be so gigantic and in the event of climate change and global warming exceeding two degrees Celsius would mean that a very large fraction of  today’s places inhabited by a large fraction of the global population would be underwater so that really makes sea level rise potentially one of the most long-term but very severe impacts of climate change.

Let’s discuss another very serious potential impact from global warming and that is the acidification of the oceans. I’ll explain in a minute what we mean by the acidification of the oceans but let’s look first at the role that the oceans play in the carbon cycle. In fact fact they play a major role because they are one of the Earth’s largest sinks for CO2 emission so as the atmospheric concentration of CO2 rises the oceans absorb the additional CO2 in an attempt to restore the balance in between the uptake and the release of CO2 at the oceans’ surface and this process directly impacts the ocean’s biogeochemistry because the CO2 reacts with water to eventually form a weak acid and this process we call the ocean’s acidification.

So why is that a problem, the acidification of the oceans. Well we only have to look at the past to look at what it would mean in the future and to realize how serious a threat it is because in the past such observed changes in the oceans’ acidity have very often been associated with large-scale extinction events, of extinction of marine species. So the problem is really that these changes in acidity are projected to increase in the future as a result of global warming and an increasing concentration of greenhouse gases emissions in in the atmosphere so that would really add another piece of very significant stress to the marine ecosystems when they’re already under tremendous pressure from human activities such as overfishing and pollution.

The oceans’ acidity already increased by about 30 percent compared to the pre-industrial level but if the temperature increased by 4 degrees Celsius then the oceans’ acidity would increase by another 150 percent and that would really have very severe negative consequences on the oceans’ ecosystems and on the marine species and therefore on food supply because we in part rely on the ocean to prove our food. More specifically it would also have very severe consequences for coral reefs and it might sound like nothing but it clearly isn’t because the coral reefs perform very important environmental services but the truth is starting at perhaps something like 550 parts per million of CO2 equivalent, so much before the temperature increase would reach four degrees Celsius, the coral reefs are expected to start to dissolve.

Let’s move on to the third type of potential impacts I was mentioning and that is the increased frequency but also intensity of some extreme weather events and and let’s discuss at first the narrow issue of rising temperatures and the heat waves resulting from these increases in temperature. The very basic and and very important point to understand is that a global warming of 4 degrees Celsius or more would not be evenly distributed across the world so that’s the world average but some parts of the world would experience a much higher increase than the world average when some other parts of the world would experience a more moderate increase but with global warming of 4 degrees Celsius on average it means that increases of six degrees Celsius or more average monthly summer temperatures would be expected in in very large regions of the world including in particular the Mediterranean, North Africa, also the Middle East but also some parts of North America so it means that recent extreme heat waves such as own those experienced by Australia, California, or Russia recently are likely to become the new normal in a 4 degrees Celsius world and tropical South America and Central Africa all the tropical islands in the pacific are likely to regularly experience summer heat waves of really unprecedented magnitude but also durations and in regions such as the Mediterranean North Africa and the Middle East but also the Tibetan Plateau almost all summer mnths are likely to be warmer than the most extreme heat waves presently experienced.

To pick only one example which I think reveals a lot: the warmest July in the Mediterranean region could be 9 degrees Celsius warmer than today’s warmest July. Do you realize what 9 degrees warmer would mean for a region like the Mediterranean and in summer for the ability, for example, to grow crops?

So the extreme heat waves in the recent years have already had very severe impacts, they have caused heat-related deaths, they’ve caused forest fires such as those we’ve seen recently in Russia or Australia, they’ve also caused very significant harvest losses as we’ve seen recently in California and the truth is that the impacts of extreme heat waves projected for a 4 degree warmer world have not yet been thoroughly evaluated by the scientists but evidence shows that they could well exceed our capacities and the the capacities of some natural systems simply to adapt to the same changes putting us into very severe risks.

Global warming of 4 degrees Celsius would also increase the frequency of heavy precipitation. This is another potential impact from global warming that would not necessarily be felt again evenly across the globe but could have very severe consequences on some parts of the planet and this is especially the case in the high latitudes and in the tropical regions in particular through tropical cyclones but also in winter in the northern mid-latitude.

Interestingly even in some regions where the total precipitation would decrease as a result of global warming, heavy precipitation could increase and that would result pretty ironically in the combined risks of drought and floods in these regions and these extreme weather events generally could induce the breakdown of infrastructure networks and really critical services such as our power production infrastructure or our water supply networks or our health services and that would really have very severe human and economic costs so to summarize the environmental but also I want to stress the economic and social risks of uncontrolled climate change are absolutely immense.

They really threaten to rollback the fruits of decades of growth and development, to undermine prosperity, to jeopardize countries’ ability to achieve even the most basic social economic goals in the future including the eradication of poverty and some in the developed world may think that we could be immune from such risk but what we just saw really proves that this is not true them.

Unabated climate change leading to global warming of 4 degrees Celsius or more would really affect all the developed and the developing countries maybe not exactly alike put the effect of such global warming would be felt in every part of the globe and the truth is that it’s our basic ability to adapt to the effects of this climate change that is at risk if global warming exceeds 4 degrees Celsius in the coming centuries

The 2-Degree Limit I

The Business As Usual Trajectory

Today we’re going to be discussing more specifically about a particular target that we have already mentioned, the objective of limiting the temperature increase to less than 2 degrees Celsius compared to the pre-industrial level, the target that was adopted by the world government in 2010 in Cancun.

We have already discussed in the previous lectures the basic elements of the climate science. We have also shown what are the key milestones on the road to Paris in 2015 when an ambitious agreement on climate change need to be reached but I’m want to start this lecture by describing what are some of the possible consequences of climate change if we don’t control the greenhouse gases emissions that we need to.

I want to be discussing where the business as usual trajectory leads us so if we continue with the current trends of rising emissions because we’ve seen already some of the impacts of climate change that are already occurring because climate change is real and is already happening in many parts of the world but if greenhouse gases concentrations continue to rise the way they’re currently doing these impacts would be really getting more and more severe overtime so let’s start this first chapter of lecture 3 by discussing where the business as usual trajectory, the continuation of the current trends, would lead us and what would be the consequences.


As we’ve said several times now the United Nations Framework Convention on Climate Change or the UNFCCC was adopted in 1992 and entered into force two years later in 1994 and by now you should all almost know by heart what is the ultimate objective of the UNFCCC, that is stated in its Article 2, which is to stabilize greenhouse gases concentrations at a level that prevents dangerous anthropogenic interference with the climate system in order to enable economic development to proceed in a sustainable manner.


The last part of the sentence is very important because it shows very well that we’re not aiming only for an environmental objective were not only aiming to protect the planet we’re aiming to protect planet in order to let economic development proceed in the future so this commitment to  stabilize greenhouse gases concentrations was re-iterated at basically each and every conference of the parties or COP of the UNFCCC since 1992 and in 2010 as we’re going to discuss in more detail today, the parties to the UNFCCC even adopted a quantified target for the first time to operationalize the objective of the UNFCCC, as I said, they agreed to limit the rise in mean surface temperature below two degrees Celsius compared to pre-industrial level and in this lecture we’re going to explain why they chose this particular target and why it is so important for sustainable development going forward but the truth is that in spite of these repeated commitments each and every year to stabilize greenhouse gases concentrations, also in spite of the growing awareness of the potentially catastrophic impacts of uncontrolled climate change and in spite of a growing number of climate change mitigation policies the anthropogenic greenhouse gases emissions, the greenhouse gases emissions that are human-induced are fall from stabilizing as opposed to the goal the UNFCCC quite the country in fact, they continue to increase, continue to increase steadily, and they even continue to increase very rapidly.312

In fact the average annual growth rate of anthropogenic greenhouse gases emissions has been even higher during the last ten years than during the previous thirty years. From the year 2000 to the year 2010 we have added approximately 1 billion tonnes or one gigatonnes as we’re going to say of CO2 equivalent for year on average in the atmosphere so remember we use the unit of CO2 equivalent to find a common metric to add together all of the different greenhouse gases of which carbon dioxide CO2 is only one. So this rise, this addition of one billion ton of Co2 in the atmosphere per year from the year 2000 to the year 2010 represents on average a 2.2 annual rate increase and so my point is that this is even more than the 0.4 billion tonnes of CO2 equivalent per year on average that we added in the atmosphere in the previous thirty years from the year 1972 to the year 2000 which represented of course an increase but an increase of only 1.3 percent per year as opposed to the 2.2 percent of the last ten years and so as a consequence of this continued and accelerated in fact increase, the anthropogenic greenhouse gas emissions reached their highest level in  human history in 2010 which is the latest data that we have available so to put a number on these emissions and one you need to remember because it’s going to be important going forward in 2010 the annual anthropogenic greenhouse gases emissions stood at 49 billion tonnes of CO2 equivalent that’s the level of the emissions per year today or in 2010 and this is what you show on this graph and you show the increase in the total greenhouse gases emissions from the year 1970 to today to 2010 and you show that divided by the main types of greenhouse gases so in particular CO2 coming both from the burning of fossil fuels and from industrial processes, the CO2 coming from a different source of human activities, the deforestation and agriculture and also methane emissions and nitrous oxide emissions.

313So the bottom line looking at this graph is that since 1970 all major sources of greenhouse gases emissions have increased. As I said, the CO2 emissions but also all the other greenhouse guess but what I want you look at in particular is to the increase in CO2 emissions from the burning of fossil fuels and from other industrial processes because this rise in particular was spectacular and is going to be the main focus of this course. It contributed to about 78 percent of the total greenhouse gases emissions increase since 1970 so today the fossil fuel related CO2 emissions are the single largest source of  greenhouse gases emissions in 2010, it reached 32 billion homes per year and represented approximately 65 percent of the total greenhouse gases emissions and since 2010 these emissions still grew further by about 3 percent between 2010 and 2011 and again by something in between 1 and 2 percent in between 2011 and 2012 and so where did these emissions come from? Which are the sectors that are responsible for these rising CO2 emissions?

Well first they came from the energy supply directly for 47 percent, then they came from the industry sector for about 30 percent. After that from the transport sector for 11 percent and the remaining CO2 energy emissions came from the building sector for 3 percent. So what are the drivers of these rapidly-growing greenhouse gases emissions? Well since 1970 economic growth and population growth were the most important drivers of this increase in emissions.


The contribution of the population growth to the increase in emissions during the past 10 years remain roughly the same compared to the previous three decades but the contribution to economic growth to the increase in emissions has risen very sharply in the past 10 years compared to the previous three decades and as we already pointed out in some of the previews lectures this is in part the result of good news and that is the very strong catch-up economic growth in the middle-income countries and in particular in China but of course that came with side effects and in particular rising levels of greenhouse gases emissions so these are the two most important factors that explain the rise in emissions in the recent past: the population rose and the economy grows.

On the other side since 1970 the energy efficiency of economic growth has pretty significantly improved. It means that progressively we were able to manage to consume less energy per unit of GDP which is the good news in a way from the climate change mitigation perspective because it means that we were also adding less unit of greenhouse gas emissions per unit of GDP produced but the bad news on the other side is that this improvement of energy efficiency was too small compared to the other driving force going in the other direction:the population and the economic growth, in particular the increase in income per capita.315

Since 1970 the carbon intensity of energy also decreased. What does that mean? Well it means, progressively we were emitting less CO2 per unit of energy consumed which again was the good news from the climate change mitigation perspective but here too this improvement in the carbon intensity of energy was much too small compared to be the necessary emission reductions to avoid dangerous climate change but what I want to point out here and what is in a fact very worrying is that during the past ten years the increased use of fossil fuels but in particular of coal relative to the other energy sources has reversed the long-standing trend of gradual decarbonization of the world energy supply.

It means that the carbon content of energy is increasing during the past ten years we emitted more carbon emissions per unit of energy we consume when instead this trend should be decreasing and it should be decreasing very strongly and very quickly. So the current trends are clearly going in the wrong direction but the question is where do they lead us? What would be the global warming consequence of these rising emissions going forward so let’s do the math.317

I mean let’s look at where we are today and and let’s look at where we would be if the current trends were continued in the coming years so where are we today? In 2011, the CO2 equivalent concentration was estimated to be at approximately 430 parts per million remember parts per million is the unit we use to measure the concentration of greenhouse gases in the atmosphere.

If the current trends continued then the concentration of these greenhouse gases in the atmosphere would exceed 450 parts per million of CO2 equivalent as soon as 2030. I am stressing this particular number of 450 parts per million because we’re going to see when we discuss two-degree limit that this is the concentration of greenhouse gases emissions that corresponds to the two-degree limit in the temperature increase but it wouldn’t stop at 450 parts per million in 2030; it would be somewhere in between 750 and perhaps even more than 1300 parts per million of CO2 equivalent by the end of the century so what would be the consequence of that amount of greenhouse gases emissions in the atmosphere?

Well that would be very dangerous because it would result in global mean surface temperature increase by the end of the century from somewhere in between 4 and 5 degrees Celsius compared to  pre-industrial level and the truth is that if you build into the analysis all the uncertainty regarding the reaction of the climate to the greenhouse gas emissions then this range could expand potentially up to 8 degrees Celsius of warming before the end of the century and the consequences of such an increase in temperature would be really catastrophic.

Towards a New Climate Change Agreement IV

From Kyoto to Copenhagen

We’re talking about the path to COP21, to the conference of the parties 21st year in Paris in 2015, a bit over a year from now. And I’ve been recounting the history of the climate change science and the climate change action. The UN Framework Convention on Climate Change, the UNFCCC, was the high water mark, in a way; 1992 Rio Earth Summit world leaders got together; they adopted a solid convention, a solid treaty, which you’ve read now I hope. And it’s a well thought-out treaty. It said let the Annex 1 countries, the high-income world, lead the way to preventing dangerous anthropogenic interference in the climate system. And after the treaty went into force in 1994, the conference of the parties, that is all the countries that are signatories to the convention, began to meet.

Berlin was COP1, Kyoto was COP3, and by the third meeting of the parties at the convention it was time to implement a protocol to put the convention into real implementation.141

This is the Kyoto Protocol. Kyoto Protocol is the only protocol that we have agreed for actually implementing the UN Framework Convention and the Kyoto Protocol was put in place in 1997. And it had a period, a vigilance period, of force till 2012. And it accomplished a little bit but not enough to really change the needle, change the course of the planet as we hurl along towards more and more human-induced climate change. Well remember that the US government as it went off to Kyoto to join in the negotiations at the Kyoto Protocol was given warning by pretty obstreperous US Senate, which in the Byrd- Hagel amendment it voted 95-nothing to say don’t you sign that protocol unless the developing country parties are also taking on obligations.

But the developing country parties in Kyoto had a rather different view and and I think the right one from the point of view of international law. Certainly they said read the UN Framework Convention. The UN Framework Convention spells out very very clearly that it is the high-income countries, the countries on the list of Annex 1, including the United States and Europe and Japan and the countries of the former Soviet Union, Central and Eastern Europe that have to move first. These are the rich countries; they have the technology; they’re the ones that are putting the carbon dioxide emissions in the atmosphere; they’re the ones that have been doing that for decades; and so the ones that bear the historic responsibility historical responsibility for raising and co2 concentrations in the first place and thereby putting the whole planet at peril. So that was a collision course already in play.

What happened at Kyoto? The Kyoto Protocol was adopted, was adopted by the Annex 1 countries and it covers the Annex 1 countries. It says that the high income world will take specific responsibilities to reduce carbon dioxide emissions by the period 2008 to 2012 as a group Annex 1 countries agreed to reduce the greenhouse gas emissions by at least 5 percent compared with the 1990 level. Now here’s a problem that we’ll be discussing in a bit more detail shortly.

You have many greenhouse gases. Six main anthropogenic greenhouse gases in the covered by the Kyoto Protocol. Carbon dioxide, methane, nitrous oxide (N3), and flourine based industrial gases. So how can we talk about 5 percent reduction? Does it mean percent of each one or by what metric should this be measured? And here will introduce a concept of the carbon dioxide equivalent of each of these greenhouse gases. By measuring how each greenhouse gas changes the planet, warms the planet, creates a greenhouse effect relative to the effect of the carbon dioxide molecule we’re able to take a sumation across the 6 human-induced greenhouse gases to come up with an overall measure, which is called the carbon dioxide equivalent of the six greenhouse gases combined. And what the Annex 1 countries said is that they would reduce the emissions a that aggregate measured as carbon dioxide equivalent by 5 percent compared to the 1990 emission levels of this group of anthropogenic greenhouse gases. I should mention parenthetically, why do I keep saying anthropogenic greenhouse gases or remember human caused greenhouse gases? It’s because there’s another very very important greenhouse gas.142

Water, which is not anthropogenic; it’s a naturally occurring greenhouse gas; it’s affected in its concentration in the atmosphere by human activity because as the atmosphere warms the atmosphere also holds more water and that water vapor has a greenhouse effect but the anthropogenic or human-caused greenhouse gases are the ones that humanity is directly putting into the atmosphere through industrial or other activities.

Now in the Kyoto Protocol, each country also took on a specific commitment of reducing its own emissions or increasing it to a limited amount as a national standard, in addition to this group commitment by the annex 1 countries of a five percent reduction. Some countries said will reduce our emissions by six percent or by eight percent. Some were even given some space for a small increase of greenhouse gas emissions because of their particular economic circumstances.

So the aggregate had to add up to a five percent overall reduction, and each country took a specific individual commitment. Then the Kyoto Protocol added a number of other features. It was not directed at specific commitments by non annex 1, that is developing countries, indeed as the original Framework Convention made clear the first efforts should start with the high-income countries. But the Kyoto Protocol invented particular mechanism, actually set of mechanisms, in this case called the Clean Development Mechanisms, to enable developing countries to join in the action in one way or another by saying we’ll take steps to reduce our own emissions voluntarily, we’re not bound at this stage by the Protocol or by the Treaty but to reduce those emissions voluntarily if someone will help us pay to do that and by the rules of the game, countries that had their own binding limits were able to perhaps exceed the limits in their own domestic emissions by engaging emissions reduction through a Clean Development Mechanism in developing countries. In other words the idea was a fairly complicated and indeed it became a pretty complicated set of mechanisms, not happily successful set of mechanisms, to link developing countries in through a voluntary but supervised approved set of means to enable rich countries to meet some of their obligations by undertaking emissions reduction projects in developing countries.

Well what can we say about the outco143mes the Kyoto Protocol. Fairly complicated. The one thing we can surely say is that the Kyoto Protocol did not succeed in changing fundamentally the direction of Earth as a whole, humanity as a whole, in heading towards massive climate damage. Interestingly the Annex 1 countries as a group, as a group, did meet 25 percent reduction. This happened in part because of actions that some of these countries took. It happened in part because of a big recession that hit the world in 2008 thereby reducing industrial activity and burning of fossil fuels. That happened in part because in the post-communist, so-called transition era, in Central and Eastern Europe and the former Soviet Union, there was a very big drop of emissions in many countries as those countries experienced a massive transformation from the very heavy industrialization of the Soviet era. So as a group the Annex 1 countries did get the emissions down by a little bit above the five percent threshold but the fact of the matter is many countries never lived up to the Kyoto Protocol.

First on the list, the United States, not only did it not live up to the Kyoto Protocol, it never ratified the Kyoto Protocol. As I have mentioned President Clinton didn’t send it to the Senate. President Bush took the United States out entirely said forget it we’re not even gonna try. And several other major fossil fuel producing and using countries that were signatories to the Kyoto Protocol all along basically just threw them off and ended up not taking them very seriously at all.

I would mention in this list two very important countries. They’re big, advanced, technologically sophisticated and major producers of fossil fuels. These are Canada and Australia. Canada discovered how to use its vast heavy oil in Western Canada in the province of Alberta to produce petroleum for world markets. Saw riches before its eyes and said were not really going to meet Kyoto Protocol. Australia is one of the great coal producing countries of the world, and coal exporting countries in the world. Australia had a minerals boom over the last twenty years. It’s become a major provider of coal for the rapidly-growing Chinese economy and Australia also said it can’t meet the conditions and basically failed to honor the Kyoto Protocol. This graphic shows in red many of the countries that fell short of what they had promised to do back in 1997 and many of the countries in blue that outperformed the reduction of greenhouse gases that they had promised in 1997.

A mixed bag. Some countries acted, other countries did not. In the aggregate, partly because of action and partly because economic circumstance the Annex 1 countries slightly reduced their emissions relative to 1990 as Kyoto called. But some failed. The United States a did not take action, even though in the end it has had a modest reduction of emissions by now partly because of economic circumstances. But one can say the following overall point about the Kyoto Protocol: whether the Annex 1 countries did or didn’t, came close, fell behind from their specific commitments, the world as a whole has continued to have a very very strong overall increase of carbon dioxide emissions and carbon dioxide equivalent emissions, that means adding in co2, nitrous oxide, methane and the flourine-based industrial gases.

144That has not slowed. Why is that? That’s because in fact while the Annex 1 countries were the dominant users of fossil fuels up to UN Framework Convention and are still the rich countries in the world with the highest per person emissions of greenhouse gases the fact of the matter is that the non-annex one countries, the developing countries, experienced a surge of energy use, surge of economic development, and therefore a surge greenhouse gas emissions after 1997. When you add in the non-annex 1 country emissions with the annex 1 country emissions, boy we have missed the point. In a sense you could say that the US Senate had a little bit of a point  saying, well the developing countries are gonna have to do something. But they didn’t have a moral or legal sense at all. The Annex 1 countries were right to say that the world had promised let the industrial world start this effort. What’s clear though is that arithmetically, when you look at the massive growth China, the other emerging middle income economies, the overall growth of the developing countries as a whole, the massive increase in fossil fuel use the in the developing countries the Kyoto Protocol did not really change the direction of the world. In terms of the upward march year by year, of more and more emissions of greenhouse gases, and therefore a trajectory of very very dangerous climate change.

Nothing like the stabilization of greenhouse gas concentrations to prevent dangerous anthropogenic interference in the climate system. Now this realization was more and more apparent in the early years. The previous decade, of course the withdrawal the US from the Kyoto Protocol was a shock, the rise of China and the world economy was an economic miracle, a great economic success, and also an amazement for the world. The fact that China is a coal-burning economy was becoming such a major emitter of carbon dioxide was also a wake-up call to a need to do more. And from Kyoto through each of the COP meetings Kyoto being COP3 and and onward, the realization came – we’re going to need a new approach. And in any event the Kyoto Protocol was set to end in 2012. So when it came to the 15th of these meetings COP15 in Copenhagen, with President Obama newly-elected promising action, with the realization that the Kyoto Protocol was nearing its expiration, with China having entered the ranks of one of the world’s most important economies and having overtaken the United States as the world’s leading emitter of greenhouse gases, the eyes were put on COP15 in Copenhagen.

This is the time. We need to make a change and COP15 in Copenhagen was the great hope in 2009 that a new approach and a new breakthrough would be met. Indeed it was the greatest gathering of world leaders on Climate Change really since the Rio Earth Summit. 115 heads of state and government came to Copenhagen. President Obama is newly elected, the highly popular US President was there, the chinese leadership, the world’s leaders assembled and this was going to be the place to make the breakthrough. The hope was that there would be an agreement in which both the Annex 1 and the non-Annex 1 countries jointly would  commit to real action, that we would be able to take a step of realism in which there would be an effective and fair allocation of responsibilities and a new approach would be made.

And it was at that point recognized that the world could actually define, based on the science, at least a limit that we must not surpass in global warming. That was the idea that many scientists had put forward, that the European Union was championing, that a two degree celsius increase of temperature would be extremely dangerous to exceed and two degrees Celsius or 3.6 degrees Fahrenheit was put as the limit. Do not cross this boundary! To go beyond the two-degree Celsius limit was rightly recognized as extraordinarily dangerous and as we’ll be discussing in the future lectures. So Copenhagen: here’s the big hope. A two degree C limit; a universal agreement; financing of specific amounts, indeed a hundred billion dollars a year for developing countries from developed countries by the year 2022 to enable the developing countries both to reduce their greenhouse gas emissions and to adapt to the ongoing climate change.

Big hopes. Great drama. Last-minute negotiations. And it wasn’t to be. The leaders just couldn’t reach an agreement. They made some declarations. They made some notable announcements – the two degrees Celsius limit, the hundred billion dollars a year – but they couldn’t agree and it was a huge emotional deflation. A huge political deflation. Kyoto hadn’t worked. Copenhagen would be it. Copenhagen collapsed and in a way we’re still picking up the pieces. It is from Copenhagen to Paris now that we put our great hopes and we resolve, all the world leaders are resolved, don’t have the Copenhagen experience again in Paris in 2015 at COP21. Let’s find a path to real success.