The last month has seen lethal, and often unprecedented, extreme weather across the Northern Hemisphere. Climate scientists say human-driven changes to the atmosphere have made events like these more likely, but how much any specific event can be attributed to human activity remains debated. Nevertheless, many regard it as plausible that human activity not only raised the risk of these events but contributed to them occurring so close together. Nature Climate Change has published an impeccably timed paper today explaining why records are not just being broken, but often shattered by wide margins.
“Weather, climate and water-related hazards are increasing in frequency and intensity as a result of climate change,” Professor Petteri Taalas, Secretary General of the World Meteorological (WMO) said in a statement released last week. “The human and economic toll was highlighted with tragic effect by the torrential rainfall and devastating flooding and loss of life in central Europe and China in the past week.”
The world has always faced extreme weather events, and before satellites provided warnings these often caused more loss of life than today. Only a few years ago most meteorologists were reluctant to blame any single event on changes to average global temperatures, but that has changed.
“Recent record-breaking heatwaves in North America are clearly linked to global warming,” Taalas continued. Twenty-seven climate researchers calculated a heatwave as extreme as the one that hit western North America in June/July would have been 150 times less likely under pre-industrial greenhouse gas levels.
Warmer air can hold more water, and climate change reports have warned of greater flooding as a consequence of Anthropogenic Global Warming for decades, so recent disasters in Germany and Henan were not unexpected. Dr Richard Matear of Australia’s CSIRO specializes in the attribution of causes of weather events, and told IFLScience there may well be a reason they are all happening together. “The path of the jet stream is very important for controlling large scale weather systems,” Matear said. “A warmer climate may make the jet stream more unstable. We’ve seen this possibly be associated with extreme cold events in winter, but it could also create summer hotspots.”
Hot air not only increases the amount of rain that can fall in a small space of time, Matear noted to IFLScience, it can also create pre-conditions for larger floods. Hot spells can kill ground cover that would usually absorb water and release it gradually. Subsequent heavy rains run off more rapidly.
Nevertheless, Matear added, the science remains uncertain in this area. Climate science has focussed more on the averages than the extremes, leaving gaps in our knowledge, Matear told IFLScience. “The corollary is that because we have a lack of information it’s not really surprising what we are experiencing is more extreme than we expected.”
When Dr Erich Fischer of ETH Zurich submitted his paper in January, he had no idea its publication would coincide with so many terrible disasters. Nevertheless, Fischer and colleagues warn events like these will become common. “Society has often been surprised by the magnitude by which recent climate extremes exceeded previous observed records,” the paper begins. The authors argue extreme events, floods and heatwaves included, will break records by ever-larger margins until warming slows down.
Where previous studies have looked at how frequently records are broken, Ficher’s paper focuses on the margin by which this occurs. It reports “record-shattering” extremes – once very rare – have become more common, and predict future acceleration. These events are driven not by the global temperature itself, but the speed with which warming occurs.
“Such unprecedented events need to be taken into account when designing critical infrastructure, such as power plants, or heatwave preparedness strategies,” the paper warns.
Climate scientists agree that rapid cuts to greenhouse gas emissions are essential to slow the pace of future disasters. Beyond this Matear told IFLScience; “People who are already stressed for whatever reason are much more prone to being impacted by these disasters. So we need to be building resilience knowing there is more to come.”