Climate change is already contributing to heat waves and torrential downpours, a new study has confirmed, and these types of extreme events will only worsen as the world continues to warm.
The study, published Monday in the journal Nature Climate Change, found that 75 percent of the planet’s “moderate daily hot extremes” can be tied to climate change. That figure means that heat events that, in a world without climate change, would occur in one out of every 1,000 days — or about once every three years — now occur in about four or five out of every 1,000 days, the study’s lead study author, Erich Fischer, told the Washington Post. Basically, climate change has upped the odds that these types of heat events will occur.
The percentage of extreme precipitation events since the Industrial Revolution that can be linked to climate change is lower — 18 percent — according to the report, but if the planet reaches 2°C of warming, that figure will rise to 40 percent. Likewise, if the earth continues to warm to 2°C, 95 percent of the planet’s daily heat extremes will be tied to climate change. The earth is currently on track to reach 2°C of warming by mid-century, and is on track for 4°C of warming by 2100.
“This new study helps get the actual probability or odds of human influence,” University of Arizona climate scientist Jonathan Overpeck, who wasn’t part of the research, told the AP. “This is key: If you don’t like hot temperature extremes that we’re getting, you now know how you can reduce the odds of such events by reducing greenhouse gas emissions.”
The study came to conclusions that were estimates for the entire globe, but noted that Africa and South America have the highest percentages of hot days tied to climate change, at 89 and 88 percent. North America has a lower amount: 67 percent, as does Europe at 63 percent.
It’s long been scientifically difficult to say that any one weather event is directly caused by climate change. Instead, one analogy that’s often used to describe climate change’s impact on weather is the “baseball player on steroids” comparison: a baseball player on steroids might have a greater chance of hitting a home run than before taking steroids, but it’s impossible to say whether or not any one home run was directly caused by the use of steroids. Instead, it’s more useful to look at his overall record of home runs while on steroids and compare it to his record before he went on steroids.
That’s similar to the way climate change interacts with weather: atmospheric warming makes it more likely that extreme weather, like heat waves and torrential downpours, will occur on average, as the study confirms. But tying one weather event to climate change isn’t as easy — or as effective — as determining whether or not that event was made more likely by climate change.
Thus, even when scientists tie extreme events to climate change, they do so by looking at how much more likely it is that event will occur today than before the earth’s current warming period started. This, for instance, was how researchers phrased the link they found between climate change and California’s historic, four-year drought: that “extreme atmospheric high pressure in this region — which is strongly linked to unusually low precipitation in California — is much more likely to occur today than prior to the human emission of greenhouse gases that began during the Industrial Revolution in the 1800s.” And, that’s why the Nature study focused on a grouping of extreme heat and rainfall events, rather than tried to attribute any one event to climate change.
“Climate change doesn’t ‘cause’ any single weather event in a deterministic sense,” Erich Fischer, a Swiss climate scientist and the study’s lead author, told Nature. “But a warmer and moister atmosphere does clearly favor more frequent hot and wet extremes.”
Numerous recent studies have illustrated the link between climate change and extreme weather events. A 2013 study from the National Oceanic and Atmospheric Administration, for instance, found that extra moisture in the air from climate change will drive a 20 to 30 percent increase in precipitation in the Northern Hemisphere by 2099. And another 2013 study found that Arctic warming, in particular, is tied to more summer heat waves, droughts, and downpours.