New climate research published this week has directly linked the level of atmospheric carbon dioxide – rather than mean global temperature – with the chance of more extreme weather events.
The research from the University of Oxford and other institutions also furthers the case for litigation against businesses and governments shown to be ignoring climate risk in their decision-making.
The paper, published this week in the journal Nature Climate Change, demonstrates that higher atmospheric CO2 concentrations directly increase temperature and rainfall extremes, irrespective of global mean temperatures. This means that there could be increased risk of dangerous weather events even if global temperatures stay within 1.5°C – providing evidence for climate policy that includes specific CO2 emissions limits as well as temperature goals.
ClientEarth associate researcher Hugh Baker, DPhil student at Oxford’s Department of Physics and lead author of the research, said: “We can now say that the accumulation of CO2 in the atmosphere itself increases the risk of key damaging weather extremes, regardless of the global temperature response. In effect it puts paid to the argument that we should wait and see if the global temperature response to rising CO2 is lower that what current modelling predicts.
“Future work is needed to confirm exactly why we see this direct CO2 effect, but current research points to a combination of circulation and cloud cover changes, and an increase in the amount of direct radiation on the Earth’s surface due to simply having more CO2 in the atmosphere.”
ClientEarth climate lawyer Sophie Marjanac said: “This important research will add to the body of evidence that could drive litigation against businesses and governments that are failing to include climate risk as part of their decision-making.
“Future litigation may depend on important science, just like this new research, and how it can inform our understanding of what effects or weather events can be totally or partially attributed to climate change and therefore what is reasonably foreseeable.”
Much of the focus of climate change mitigation has been on the goal of limiting warming to 1.5°C, agreed at the 2015 United Nations climate summit in Paris.
However, scientific attention has now turned to analysing in more depth the climate response to the atmospheric CO2 concentrations required to limit warming to 1.5°C. Researchers from Oxford and other institutions participating in the HAPPI (Half a degree Additional warming, Prognosis and Projected Impacts) project simulated future climate under the range of all CO2 concentrations that might be consistent with 1.5°C of global warming.
In the models, CO2 levels at the higher end of this range were shown to directly increase Northern Hemisphere summer temperature, heat stress, and tropical precipitation extremes.
The research points to the need to set explicit CO2 concentration goals to limit high-impact weather extremes.
The research was carried out in collaboration with researchers at the University of Melbourne, ETH Zurich, the University of Bristol and the National Institute for Environmental Studies in Tsukuba, Japan. The research paper can be viewed here.