Something I’ve always struggled with when it comes to climate change is understanding the actual impacts of anthropogenic global warming. I think I understand the big picture quite well. If we continue to add greenhouse gases to the atmosphere, we will sustain a planetary energy imbalance, which will cause the climate to warm. This will also intensify the hydrological cycle; there will be more evaporation and precipitation and, in particular, we will see an increase in the frequency and intensity of extreme precipitation events. We will also probably see an increase in the frequency and intensity of some extreme weather events, although these events can have complex causes and so the outcome here can be less certain.
However, what I understand less is the actual impact of these changes. There is, however, a recent paper by Richard Betts and colleagues that looks at this, specifically in the context of the Paris targets. The paper is called Changes in climate extremes, fresh water availability and vulnerability to food insecurity projected at 1.5°C and 2°C global warming with a higher-resolution global climate model and has already been discussed by John Abraham in The Guardian. What they did in this study was quite interesting. They used a high resolution land and atmosphere only simulation, with sea surface temperatures and sea ice concentrations as inputs. The latter came from a subset of the CMIP5 simulations. The idea being that this provide be a representation of the range of potential internal variability.
The results, however, seem reasonably obvious. For example, the
simulations project consistent increases in temperature-related extremes, with larger changes at 2°C compared to 1.5°C and local changes being larger than the global annual mean.
changes relating to the water cycle are complex, both in their geographical pattern and in the variation between different models. The length of flooding events generally increases across world in all models, but maximum rainfall can either increase or decrease depending on locations. ….. Worldwide, most impacts broadly tend to increase with global warming in most areas.
Vulnerability to food insecurity
increases more at 2°C global warming than 1.5°C in approximately three-quarters of countries assessed. The vulnerability increase can arise from increases in either flooding or drought.
So, there is a tendency for there to be an increase in temperature-related extremes, that is larger at 2oC than at 1.5oC. However, it can be complex, and there is regional variability. We would expect these changes to lead to an increase in vunerability to food insecurity in many regions, but not all, and for this increase to be greater at 2oC, than at 1.5oC.
However, I’m not really sure what to make of this, other than it being roughly what one would expect. Of course, if we do not keep warming below the Paris target levels, then it would be important to understand where to focus our activities. However, there are still impacts that this study does not include, such as sea level rise and ocean acidification, so we can’t really conclude that this is all that we would face.
Does it suggest that we should focus less on mitigation? No, I don’t think so. Keeping warming below 2oC is going to be extremely difficult, and keeping it below 1.5oC may well be virtually impossible. This study is consistent with the impacts becoming more severe with increasing warming. If we would like to avoid the even more severe impacts that would likely occur if we warm much beyond 2oC, then we really should be thinking of ways to reduce our emissions, and should probably be aiming to start sooner, rather than later. At the same time, some of the impacts are probably unavoidable, and so we should also be thinking of how to respond to what we will almost certainly face, which is why these kind of studies can be important.