The summer of 2021 has already unleashed a rash of extreme events that raised eyebrows of even the most seasoned meteorologists, and fingerprints of the human-caused climate crisis are all over them. The first sweltering heatwave baked the western U.S. in mid-June, hitting temperatures never before seen in seven states. Both Phoenix and Tucson, Ariz., broke daily records six days in a row with heat topping a life-threatening 115 degrees Fahrenheit.
Not to be outdone, the normally cool, moist Pacific Northwest withered under a reinvigorated dome of heat at the end of June that may go down in history as the world’s most intense on record. Hundreds of people and a billion sea creatures perished. At the moment, yet another surge of sweltering temperatures — the fourth major heatwave in five weeks — is smothering the northern Rockies and northern plains. Meanwhile, the Midwest and Mississippi Valley are being inundated with repeated bouts of heavy precipitation and severe storms.
North America is not alone, however, in facing Mother Nature’s frenzy: Europe and Siberia have also suffered vicious heatwaves, and last week Germany bore the brunt of a slow-moving deluge that destroyed scores of homes and killed nearly 200 people.
This is just a partial list of such events. Summer is barely half over. Record drought conditions are already fueling wildfires. The peak of the Atlantic hurricane season is still weeks away. Oh my.
To be clear, summer heatwaves and floods have always happened. What’s new is that the intensity, persistence, location, frequency and expanse are beyond what we call normal. Long-standing records are being smashed by large margins. This trend is not a surprise to scientists who study impacts of society’s assault on the climate system, although the pace of worsening weather is faster than forecasted.
New research methods can assess the role of climate change in making extreme weather events more likely or more intense, and the message is now loud and clear: By burning fossil fuels, cutting down forests, harming natural ecosystems and over-fertilizing croplands, humans are changing the atmosphere’s composition in ways that are affecting weather patterns around the globe. The historic Pacific Northwest heatwave, for example, would have been “virtually impossible” without the boost from human-caused climate change.
Some of these weather-climate connections are direct and intuitive. As the thickening blanket of heat-trapping gases has warmed the globe, heatwaves are hotter, bigger and longer-lasting. They will continue to intensify until we stop using the atmosphere as a dumpster for the waste gases from burning fossil fuels. And with higher temperatures comes more evaporation. Warmer air can hold more water vapor, which strengthens storms and produces heavier precipitation. Heavy rainfall events are already occurring much more often — floods in the Midwest and Europe are just the most recent examples.
Counterintuitively, heat-boosted evaporation also exacerbates drought by sucking water out of soil. Dried out soil heats up faster under a searing summer sun. And that hotter surface further intensifies the heatwave, setting up a vicious cycle that feeds a persistent dome of hot air. The multi-year drought now underway in western U.S. states is the most extensive since the Drought Monitor was established in 2000. As of July 13, over half of the western states was experiencing severe-to-exceptional drought, an improvement from its peak of 81 percent coverage two weeks prior. Drought and heat are two of the main ingredients for wildfires, and this summer’s fire season is already off to a worrisome start, beating last year’s blistering pace by 38 percent.
While these connections between a warming planet and weather extremes are straightforward, other links are more complex and the focus of ongoing study. For example, we know the globe is not warming evenly, and a growing body of research suggests these disparities may be affecting the major wind patterns that create and steer weather systems around the temperate latitudes. Not only have land areas warmed more than oceans, but far northern latitudes are heating up about three times faster than the global average.
Disproportionate northern warming means a smaller north-south temperature difference — the main force driving the meandering river of high-elevation winds known as the jet stream. As this temperature difference weakens, so do the westerly jet-stream winds. Slower winds and differential warming patterns have been linked with wavier jet-stream patterns that cause stagnant summer weather systems.
Persistent hot, dry or rainy conditions can turn into the very extremes we’ve seen unfolding again and again in recent weeks — heatwaves, drought and flooding. Tropical storms may also be feeling the effects of slower steering winds, resulting in the devastating floods and destruction wrought by sluggish hurricanes like Harvey, Florence and Dorian.
The increased frequency of extreme weather events — estimated to have tripled since 1980 — are just symptoms of the underlying disease. It’s time for emergency-room-style triage: a rapid and drastic reduction in our emissions of heat-trapping gases while also bracing for worsening events to come.
While we can’t avoid the near-term escalation in disruptive, deadly and expensive climate-fueled extremes, we can control how much worse they become in our children’s and grandchildren’s lifetimes. But time is running out, and Mother Nature’s tantrums won’t wait.
Jennifer Francis Ph.D., is a senior scientist at the Woodwell Climate Research Center in Falmouth, Massachusetts. Her research focuses on connections between climate change, particularly in the Arctic, as well as extreme weather events in North America and Eurasia. Follow her on Twitter: @JFrancisClimate