Are extreme events worse than climate scientists projected?
After the record-shattering heat in North America came flooding in Germany, one of the richest countries in the world and proud of its engineering prowess — together these extreme weather events reached death tolls in the hundreds. Away from those disasters that captured headlines in the global north, the same weeks saw devastating floods in China, Afghanistan, Pakistan and Myanmar.
As these crises have unfolded, an important question is being asked: Are extreme events, driven by climate change, progressing more quickly and dangerously than scientists like me had projected?
It is hardly news that climate change is driving increasingly extreme weather. Heat records are being broken every summer. We knew this would happen in a warming world — and that is what we are seeing. We also have known for a very long time that heavy rainfall events are becoming more frequent and more intense across the globe, although by a smaller margin than heat.
Heat and heavy rain are the two extremes for which the change has been most clear for many years — and heatwaves are by far the deadliest extreme events in the developed world. So, if you are responsible in local authorities for disaster prevention you would have made sure that these two types of extremes are top priorities for protecting the public. You’d think. But it is not what has happened, and the consequence is many hundreds of unnecessary deaths this summer alone.
The death toll and lack of preparedness and the ignorance of even the possibility that weather can be deadly is shocking for me as a scientist. But being shocked by the impacts of the extremes is not the same as being surprised by the events themselves.
Media attention is now turning to whether or not the heatwave and floods were predictable — with some articles suggesting that climate models got it wrong and had completely underestimated what we now observe. That is not true.
The heatwave in North America was certainly remarkable, but it was within the range of what climate models have predicted. In an extremely timely study last week, scientists from the ETH Zurich not only demonstrate that models do indeed predict this type of event — but that as the world rapidly warms, we should expect heat records consistently to be shattered by up to 5 degrees Celsius. This is just the predictable consequence of continuous rapid warming: It doesn’t even require tipping points, non-linear feedbacks or misbehaving jet streams; all of which could also play a role and there is justified scientific debate about this role in the real atmosphere and those in climate models. Models are far from perfect, and there is plenty to improve, but the events that seem to have inspired this debate are very much not absent from models. They have been predicted and here they are.
Put another way: The heatwave was a freakish event; we have always expected such unlikely things to happen somewhere in the world quite often — but today’s freakish events are very different from the freakish events of the past. Every past decade has been warmer than the one before and warming faster than the one before because the world is emitting ever more greenhouse gases faster. This means we are moving quickly away from the climate our experiences and observations have been made in. A one-in-a-thousand-year heatwave in 2021 is very different to thousand-year heatwaves we might have recorded in the 1930s.
And some events that seem extreme, like the European summers of 2018 and 2019 were not exceptionally rare heatwaves in today’s climate that is 1.2 degrees Celsius warmer than it was before we started burning coal, oil and gas. They still broke records, in places by large margins, because the climate during most of the period when records were kept was different.
The situation is a bit different when it comes to heavy rainfall. The effect of climate change on these types of events is smaller than for heat so while some of the recent events are record-breaking, they did not break the records by a huge margin. At the same time, we know from basic physics and research based on climate models and observations that heavy rainfall increases in a warmer climate. This means, not only do we know that floods are something societies need to be better prepared for.
It can sometimes be difficult to take seriously the results of climate models that project extreme events that are far outside our human experience. There certainly are gaps in climate science, not least the huge imbalance in climate science toward studying the global North. But as the consequences of continued greenhouse gas emissions become increasingly devastating, our response should be to take the warnings of climate models more seriously, not less — and to prepare accordingly.
Friederike Otto, Ph.D., associate director of the Environmental Change Institute at the University of Oxford and an associate professor in the Global Climate Science Programme. Follow Otto on Twitter: @FrediOtto