Home Earth Over half of extremely hot days linked to man-made climate change

Over half of extremely hot days linked to man-made climate change

One weapon in the arsenal of climate change deniers is the idea that, somehow, climate change should bring forth heretofore unseen weather events. Real “wrath of God” type stuff. Very hot days, or exceptionally heavy rainfall, so the thinking goes, don’t mean much because those have always been a part of the climate landscape. That’s true, note scientists at the Swiss Federal Institute of Technology – it’s just that those extreme events are far more likely now, and up to 75% of them are the result of climate change.

One problem with measuring extreme weather events is that what seems extreme in one location may be routine in another. What constitutes a hot day in Vermont, for instance, might sound like a nice reprieve to someone in central Florida. What’s more, the idea that climate change has or will result in all extreme weather events (hail, tornadoes, etc.) becoming more frequent is pretty easily debunked, so far. However, after gathering data from weather stations from around the world, Dr. Erich Fischer and his colleagues found a very clear trend: Hot extremes have become both more intense and frequent since the 1950s, and heavy rains are on the rise as well. What’s more, scientists are able to attribute the increases to man-made climate change.

“After Europe’s summer-long heatwave in 2003, scientists concluded that although hot periods of this type can occur without human influence, global warming has more than doubled the likelihood of these hot summers in Europe. In turn, these scientists attributed more than half of the probability of the hot summer in 2003 to warming caused by humans. Like someone cheating with loaded dice in order to roll more sixes, so did warming increase the odds of a heatwave that summer,” Fischer wrote.

Scientists often struggle to determine the degree to which human interference contributes to extreme weather events, a problematically difficult equation for obvious reasons. Instead, Fischer and his co-authors took a different approach – how much more likely does climate change (whatever its cause) make these extreme events? They found that well over half of worldwide heat extremes and about a fifth of precipitation extremes can be directly linked with global warming. In their paper, they also demonstrate that the rarer and more extreme the event, the more it can be attributed to the man-made components of climate change.

Fischer also says that seemingly minor differences in global warming targets could have a massive impact on extreme weather events, which affect the human experience much more acutely than the temperature increase itself.

“If temperatures rise globally by 2˚C, we expect twice as many extreme heat events worldwide than we would with a 1.5˚C increase. These global warming targets, which are discussed in climate negotiations and which differ little at first glance, therefore have a great influence on the frequency of extremes,” he wrote.

He notes that while climate change models aren’t perfect (they can’t capture small, localized weather events, for instance), the observations of extremes recorded over the last several decades correspond well with what the models predict.

As the scientists say, it’s not terribly complicated: As the temperature rises, hot areas get hotter. More moisture works its way into the atmosphere, and it has to fall somewhere eventually, making already wet places wetter. Places that already experience drought, like California, will only struggle more as the hottest days become hotter and more frequent.