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.

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.

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.

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.

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.

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.

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.

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.

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.

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