Heat waves, heavy rainfall and extreme drought: Man has already changed the climate catastrophically. What we currently refer to as a mega drought could actually already be a new normal in the western United States and in the Mediterranean region, as the international research team led by Samantha Stevenson from the University of California in Santa Barbara reported on Monday. By the end of this century, about 60 percent of the world’s land area will experience average conditions that fall within what we would now call extreme drought or flooding.
The researchers argue that given these profound changes, it is questionable whether the current definition of mega-events still makes sense. “When you talk about droughts, it is suggested that the event will soon pass,” says co-author and climate scientist Flavio Lehner from Cornell University.
“But if it’s the new normal, it’s clear that you have to adapt to the extremely dry conditions in the long term,” said the researcher, who previously worked at ETH Zurich, in an interview with the Keystone-SDA news agency.
Return to old normal unlikely
The study also revealed that the new normal will be interrupted more often than today by severe, short-term precipitation events and severe dry phases that immediately follow.
“In many areas it no longer makes sense to hope that things will go back to how they used to be,” says Lehner. It is therefore all the more important not only to design irrigation systems, protective walls or dams on the basis of historical data, but also to incorporate model data into the planning.
Action is urgently needed
In the climate models, the researchers calculated a “worst-case scenario” in which the earth would warm up by five degrees compared to pre-industrial times. The earth is currently heading for a warming of around three degrees. “If we stay on this course or if we can slow down global warming even more, the effects will not be quite as dramatic as shown in our study,” says Lehner. But the trends remained the same – droughts just wouldn’t be quite as dry, extreme events just wouldn’t be quite as frequent.
It was not until the end of February that the Intergovernmental Panel on Climate Change (IPCC) emphasized the urgency of taking action in the second part of its sixth status report. The effects and risks of climate change can therefore be mitigated to a limited extent if people and nature adapt to the changed conditions – and greenhouse gas emissions are now drastically reduced. Because the clock is ticking according to the experts.
Double extremes are becoming more common
In a study also published on Monday, Lehner and colleagues from the University of Bern, among others, examined the probability of the occurrence of so-called “double climate extremes” – a double whammy of extreme heat and severe drought.
While such double extremes statistically occurred once every 33 years in the middle of the 20th century, this will be four times more frequent in a world that is two degrees warmer. The researchers report this in the journal “Nature Climate Change”.
The damage caused by such combined extreme events increases, which poses major challenges for agriculture. Because heat boosts evaporation, which would require more irrigation – but because of the drought, water is in short supply.
Precipitation pattern crucial
Using the simulations, the researchers also found out that the precipitation patterns will determine whether and how often droughts and heat waves will occur at the same time. Because even with two degrees of warming, every drought anywhere in the world will be accompanied by a heat wave.
However, the development of precipitation patterns is subject to great uncertainty because the dynamics of many atmospheric processes are not yet well understood. “There is still a great need for research here in order to be able to estimate the frequency of double extremes even more reliably,” says Lehner.
–
