But a new study, published in Nature Climate Change, argues that shortcomings in the understanding of how climate change and atmospheric circulation interact shouldn’t stop us from asking a different question: did climate change play a part in worsening the weather event, even if it would have occurred without climate change?
“Assume that that weather system would have occurred anyway,” Kevin Trenberth, senior scientist with the Climate Analysis Section at the National Center for Atmospheric Research and an author of the study, told the Washington Post, “and then ask the question how the change in the environment affected the outcome, in particular through higher temperatures, greater rainfalls, more rapid drying in the case of the drought — and these things are answerable.”
To look at how an extreme weather event might have been influenced by climate change, Trenberth and his colleagues set aside atmospheric circulation dynamics to look at another part of atmospheric science: thermodynamics, which is how moisture and temperature interact. Thermodynamics says that hot temperatures lead to greater evaporation of moisture, and hot air can also hold more moisture. This is why scientists think that with climate change, extreme precipitation events are going to become more common — the atmosphere, as it warms, will simply be able to hold more moisture that can come down as rain or snow.
In understanding how a specific weather event is related to climate change, Trenberth and his colleagues present a few questions researchers might ask, such as:
- Given a particular weather pattern, how were the temperatures, precipitation, and associated impacts influenced by climate change?
- Given a drought, how was the drying enhanced by climate change and how did that influence the moisture deficits and dryness of the soils, and the wildfire risk? Did it lead to a more intense and perhaps longer-lasting drought, as is likely?
- Given a flood, where did the moisture come from? Was it enhanced by high ocean temperatures that might have had a climate change component?
- Given a heat wave, how was that influenced by drought, changes in precipitation, and extra heat from global warming?
- Given extreme snow, where did the moisture come from? Was it related to higher than normal surface sea temperatures off the coast or father afield?
- Given an extreme storm, how was it influenced by anomalous surface sea temperatures and ocean heat content, anomalous moisture transports into the storm, and associated rainfall and latent heating? Was a storm surge worse because of higher sea levels?