This summer's extreme weather is a sign of things to come

Two-thirds of the way through the year, 2023 seems destined to be remembered as the year that extreme weather events left the Northern Hemisphere reeling.

The summer months brought a litany of extreme weather events: Wildfires across Canada. Flooding in Vermont. An “unusually early and aggressive start” to the Atlantic hurricane season. A devastating wildfire on the Hawaiian island of Maui, fueled by heat and cyclonic winds, that all but destroyed a historic town..

According to the European Union’s Copernicus Climate Change Service, the three-month period from June to August was the warmest northern hemisphere summer ever recorded, 1.2° F above the 1991-2020 average and 0.5 degrees higher than the previous record.

And a new analysis by the nonprofit organization Climate Central has drawn a direct line between those temperatures and climate change, arguing that nearly half of the global population—3.9 billion people—experienced 30 or more days between June and August with temperatures made at least three times more likely by climate change.

“Virtually no one on Earth escaped the influence of global warming during the past three months,” Andrew Pershing, Climate Central’s vice president for science, said in a press release. “In every country we could analyze, including the southern hemisphere where this is the coolest time of year, we saw temperatures that would be difficult–and in some cases nearly impossible–without human-caused climate change. Carbon pollution is clearly responsible for this season’s record-setting heat.”

The climate connection 

Connecting the dots between climate change and this summer’s extreme weather is complicated, but some scientists are feeling increasingly confident in their ability to do so.

Speaking at a press briefing to announce the Climate Central findings, Friederike Otto, a physicist at Imperial College London said that the intensity of wildfires in Quebec that blanketed large areas of the U.S. in smoke “was about 50 percent more intense because of human-induced climate change,” and that the weather conditions that allowed the fires to flourish were “made at least twice as likely” by a warming climate.

But Otto, a co-founder of the World Weather Attribution initiative, acknowledged that, because of the multiple components involved in driving extreme weather events, “quantification is quite different depending on different methods and different models.”

For that reason, some scientists prefer to speak in more general terms about how climate change has driven the year’s extreme weather.

“We can say, with a great deal of confidence, that we would not be seeing the unprecedented weather extremes we saw play out this past summer in the absence of human-caused warming from fossil fuel-generated carbon pollution,” says Michael Mann, director of the Penn Center of Science, Sustainability and the Media, in an email.

But he argues that analysis that attempts to attribute specific events to climate change can sometimes miss the bigger picture of how warming affects broader, longer-term weather patterns, such as by distorting the jet stream, the band of westerly winds that circles the northern hemisphere. A number of researchers are concerned that a warming Arctic is weakening the jet stream, allowing hot air from the tropics to flow north and prolonging heatwaves, fueling wildfires, and melting the Arctic.

For that reason, explained Mann, whose latest book on climate change is publishing later this month, “I often prefer to talk about how climate change is impacting the basic processes relevant to all of these events, which includes not only the obvious fact that heat waves are more frequent and intense on a hotter planet, but the fact that hotter continents in the summer lose more moisture through evaporation.”

What might seem like just a heat wave can set off a cascade of disasters, Mann notes. Worse droughts lead to more damaging wildfires. And a warmer atmosphere can hold more water vapor, so when rain does arrive it is often heavier and more likely to lead to flooding.

Adds Stephen MacAvoy of the Department of Environmental Science at American University, the key to understanding the future of weather is to assume an increase in the “extreme and erratic.”

“Your current conditions won't necessarily be exacerbated,” he explains. “If it's dry, it doesn't necessarily get drier. And if it’s wet, it won’t necessarily get wetter. But there’s a good chance it’s going to be odd, frankly. I mean, Texas didn't expect to get frozen in 2021.”

Redefining summer weather

Where climate researchers are in accord, however, is that this past summer will not prove anomalous. We may not experience similarly widespread extreme conditions next year or the year after, but we will experience them again and again.

“In terms of extreme weather:—well, we have to get used to that,” says MacAvoy. But he takes umbrage at the notion that 2023 presages a “new normal.”

“I have issues with that phrasing,” he explains. “Because normal implies stable, and we're not in a new normal, because everything is still changing, and it's going to continue to change.”

Mann agrees.

“I've sometimes favored the term ‘a new abnormal,’ but the basic problem with this framing is that it makes it sounds like we've arrived in some new state of the climate and just have to figure out how to adapt to it,” he explains. “But it's much worse than that. As we continue to warm the planet, all of this gets worse and worse.”