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.
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.
The 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.
So 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.