In a new study published on 27 November, scientists have said that state-of-the-art climate models drastically underestimate how much extreme rainfall increases under global warming. The researchers warned that this could lead to a future with more destructive floods, unless greenhouse emissions are reduced.
Researchers from the Potsdam Institute for Climate Impact Research (PIK) in Germany said these changes follow the physical theory of the classic Clausius-Clapeyron relation of 1834, which established that warmer air could hold more water vapour.
“Our study confirms that the intensity and frequency of heavy rainfall extremes are increasing exponentially with every increment of global warming,” explains Max Kotz, lead-author of the study that was published in the Journal of Climate. Kotz adds: "State-of-the-art climate models vary on how strongly extreme rainfall scales with global warming and that they underestimate it compared to historical observations.”
According to a news release, the researchers at PIK analysed the intensity and frequency of daily precipitation extremes over land in 21 state-of-the-art climate simulations (CMIP-6) and compared the changes projected by CMIP-6 models to those observed historically. The method they applied draws on pattern-filtering techniques, allowing them to separate which changes in the climate system are forced by human emissions, and which are not.
While most land-areas exhibit increases in both the intensity and frequency of extremes, stronger increases are typically found across tropical regions, the study reveals. Significant changes most often occur across the tropics and high-latitudes, like in Southeast Asia or Northern Canada.
The fact that these changes follow the Clausius-Clapeyron relation underpins the fact that thermodynamics, i.e. temperature and not dynamics, i.e. winds, dominate the global change of extreme rainfall events, the news release adds.
“Climate impacts on society have been calculated using climate models. Now our findings suggest that these impacts could be much worse than we thought. Extreme rainfall will be heavier and more frequent. Society needs to be prepared for this,” PIK department head and author of the study Anders Levermann said in the release.
“The good news is that this makes it easier to predict the future of extreme rainfall. The bad news is: It will get worse, if we keep pushing up global temperatures by emitting greenhouse gases,” Levermann adds.
According to an AFP report, the study comes at a pivotal moment as countries prepare to meet at the COP28 summit in Dubai beginning later this week, amid fears it could soon be impossible to limit long-term warming to the 1.5 degrees Celsius scientists say is necessary to curb the worst effects of human-caused climate change.