Heat Domes Are Hotter and Lingering Longer—Because of the Arctic

Scientific American

4 days ago

CLIMATEWIRE | Temperatures are finally falling in the eastern U.S. as a vicious heat dome begins to subside. But such sweltering early-summer heat will only get more frequent in the years to come.
That's because this week's heat wave — which tumbled century-old temperature records in some areas — was clearly influenced by climate change, scientists say. The heat dome is just one consequence of the "stuck" weather patterns that are on the rise as the planet warms.
A recent study, published June 16 in the scientific journal Proceedings of the National Academy of Sciences, warns of the rising dangers of such long-lasting weather patterns, which can prompt not just heat waves but also heavy rainfall and floods.
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This week, the heat index — or what the temperature actually feels like to human skin — rose well above 100 degrees in many areas. Minneapolis also broke a daily high last set in 1910 when the city hit 96 degrees Saturday, and New York City tied its 1888 record of 96 degrees in Central Park on Monday.
The new study suggests that the phenomenon behind such extreme weather may have a surprising origin: rapid warming, hundreds of miles away, in the icy Arctic.
Researchers from the University of Pennsylvania and Lawrence Berkeley National Laboratory investigated natural atmospheric patterns known as planetary waves. These wobbly air currents meander up and down as they circle the globe — and when they intensify, they sometimes lead to storms or heat domes stagnating in place for days at a time.
The study looked at the frequency of planet wave "resonance events," or temporary intensifications. They found that these kinds of stalled atmospheric patterns have tripled over the last 70 years. At the same time, extreme summer weather — like heat waves and floods — have also grown more common.
Climate models have long predicted that these patterns would occur more frequently with climate change. But the new study is the first to demonstrate that it's already happening, the authors say.
Still, the exact causes of these planetary wave events are an active research topic.
Some research suggests that rapid warming in the Arctic — which is heating up as much as four times faster than the rest of the globe — is altering the atmosphere in ways that shift the jet stream south and affect the planetary waves. Other studies suggest that tropical warming may actually yank the jet stream poleward. And some researchers say planetary waves may be impacted by a tug-of-war between these two influences.
Computer models aren't always able to fully simulate these physical responses, making it a difficult subject to study. Scientists have been investigating — and debating — the exact physical effects of global warming on atmospheric circulation patterns for years.
But the new study adds to the evidence that Arctic warming plays a role. It shows that periods of warmer temperatures in the high latitudes are associated with increases in planetary wave resonance events. It also demonstrates that the growing global contrast between land temperatures and ocean temperatures — since land is warming faster than water worldwide — has also played a part.
Other events have an influence as well, the research suggests. Strong El Niño events, which cause temperatures to warm in the Pacific Ocean, also seem to drive temporary spikes in weather-stalling planetary wave events.
In short, multiple factors — both natural and human-caused — play a role. But climate change is a definite influence, the study notes, warning that extreme summer weather will keep intensifying as global temperatures rise.
Other research also points to the fingerprint of climate change on the recent heat.
Climate Central, a nonprofit climate science and communication organization, has developed a scientific metric known as the Climate Shift Index that evaluates the influence of global warming on temperatures around the world.
The tool estimates that high temperatures in large swaths of the eastern U.S. over the last few days were at least five times more likely to occur because of human-caused climate change.
'The extent of this early summer heat dome over the United States is remarkable,' said Climate Central scientist Zachary Labe in a statement. 'It is a stark reminder that climate change is making these dangerous and oppressive heat waves far more likely, affecting millions of people.'