Hotter, faster, stronger: That isn’t a tagline for the next blockbuster superhero movie. This is what climate change is doing to many extreme weather events. As the planet warms, heat waves are getting hotter, wildfires are moving faster and burning larger areas, and storms and floods are becoming stronger.
These effects are no longer a future or distant concern: They are affecting us — all of us — here and now. The last week of July, in Ontario, where one of us, Dr. Hayhoe, was visiting family, the sun was orange and hazy, and smoke from the wildfires that blazed across Canada hung in the air. The week before, Dr. Otto anxiously checked in with family in Rhineland-Palatinate, the region in western Germany where heavy rainfall caused floods that took more than 150 lives.
We’re both climate scientists, so when a disaster happens, we’re often asked: Is this climate change or just bad weather?
While it is a natural human inclination to want to categorize things in simple terms, how climate change affects our weather is not an either/or question. We are already living in a world that is two degrees Fahrenheit warmer than it was at the outset of the Industrial Revolution. That means that every weather event is already superimposed over the background of a changed climate.
The more precise question to ask is this: Did climate change alter the severity, frequency or duration of this event? Increasingly, the answer is a resounding yes. And thanks to cutting-edge science, we’re starting to be able to put some numbers on it, too. This type of research is called “attribution.”
How can science tease out the exact contribution of human-caused climate change to a given event without a separate, otherwise identical, but human-free earth to compare it to? The first step is to characterize the event using observations: how long and hot was the heat wave, or how much rain fell during the storm, or how strong was the hurricane.
Then, we turn to our climate models. These are sophisticated physics-based simulations of the atmosphere, ocean and land surface that are run on powerful supercomputers. Because we know very well the amount of greenhouse gases humans have added to the atmosphere, we can remove the human influence from climate models’ atmospheres to create a world without climate change. Using the models, we can then identify how strong, how long, how big, and how likely the same event would be in that imaginary world.
The effect of climate change is the difference between what happens in a world without human influence and what happened in the real world. When scientists find that, say, what is now a one in a 100 years event in the real world would have occurred only once every 200 years without climate change, this doubled risk can be attributed to climate change.
Attribution matters because our human brains prioritize immediacy. We are wired to feel more concerned about a small leak in our roof than we are about a few degrees rise in ocean temperature 50 or 500 miles away. But when your home is in Houston, an increase of a few degrees in ocean surface temperature turns a distant problem into an immediate catastrophe, as when rain from a storm like Hurricane Harvey deluges your home for days upon days.
That storm hit Houston in August 2017. It wasn’t until December of that year, though, that the first attribution study was published showing that climate change made a storm with as much rainfall as Hurricane Harvey three times more likely. It took until 2020 for scientists to calculate that three-quarters of the tens of billions in economic damage suffered during the storm stem from the additional rainfall amounts attributed to human-caused climate change. This is a stunning number, but by then, the news cycle had long since moved on.
This is why new rapid attribution analyses are so important. Take the heat wave this summer in the Pacific Northwest and British Columbia, which resulted in an estimated hundreds of heat-related deaths, ruined crops and wildfire outbreaks. The town of Lytton, British Columbia, broke the temperature record for Canada three days in a row. On the fourth day Lytton was all but destroyed by wildfire. These events were so extreme that they were very difficult to imagine, even for climate scientists like us, just two months ago.
Dr. Otto was part of an international team of researchers organized by the World Weather Attribution initiative who conducted a rapid analysis of the event. They found that human-induced global warming made the heat wave 3.6 degrees Fahrenheit hotter and at least 150 times more likely to occur. The report garnered headlines in part because it was released just nine days after the heat wave occurred, so it was still news.
The attribution team is working on its next report, analyzing the heavy rain and flooding in Germany and Belgium in July. We won’t have exact numbers until the analysis is completed this month, but we do know from basic physics that in a warmer atmosphere, the chance of heavy rainfall is higher. The just published report by the Intergovernmental Panel on Climate Change has shown this very clearly.
As extreme weather increasingly becomes the new norm, this is how rapid analysis and attribution science can help us more clearly and succinctly label and calculate the ways climate change multiplies the threat of extreme weather and puts us all at risk. But we don’t need to analyze any more events to know we need to act, and quickly.
The evidence and the data is already clear: The faster we cut our emissions, the better off we’ll all be.
Katharine Hayhoe is a professor at Texas Tech University and the author of the forthcoming book “Saving Us: A Climate Scientist’s Case for Hope and Healing in a Divided World." Friederike Otto is a climate scientist at the University of Oxford and the author of “Angry Weather: Heat Waves, Floods, Storms, and the New Science of Climate Change.”
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