In the old days, we could escape the summer heat by heading north — to the Adirondacks in the East or to the cool, forested Pacific Northwest in the West.
But this is not your grandparents’ climate.
And though we’re only one week into official summer, the characteristically cool Pacific Northwest has turned into a caldron of triple-digit temperatures, with Portland, Ore., and Seattle reaching record highs of 115 and 108 degrees, respectively. That’s unseasonably hot — for Phoenix.
The western United States is currently under the influence of an epic heat dome, an expansive region of high atmospheric pressure characterized by heat, drought and heightened fire danger. It’s being called a once-in-a-millennium event, which means you might have expected to witness it once during your lifetime — if you happen to be Methuselah of biblical fame.
All bets are off when one accounts for human-caused warming. It no longer makes sense to talk about a once-in-a-century or once-in-a-millennium event as if we’re just rolling an ordinary pair of dice, because we’ve loaded the dice through fossil fuel burning and other human activities that generate carbon pollution and warm the planet. It’s as if snake eyes, which should occur randomly only once every 36 times you rolled a pair of dice, were coming up once every four times.
Might a heat dome have developed out West this past week without climate change? Sure.
Might it have been as extreme as what we’re witnessing without climate change? Almost surely not.
If we step back a bit, we see a disturbing pattern. With this latest heat wave, Canada observed its hottest day on record: 116 degrees in British Columbia. Less than a year ago, the United States set its own record — the highest temperature reliably recorded on the entire planet, in fact — with a 130 degree reading in Death Valley in Southern California.
Yes, the dice have been loaded, and not in our favor. If climate change were a casino, we’d be hemorrhaging cash. Wildfires, heat waves, floods and superstorms, many exacerbated by climate change, collectively cost the United States nearly $100 billion in 2020. As the climate advocate Greta Thunberg so poignantly put it, “Our house is on fire.”
We’ve long known that a warming climate would yield more extremely hot weather. The science is clear on how human-caused climate change is already affecting heat waves: Global warming has caused them to be hotter, larger, longer and more frequent. What were once very rare events are becoming more common.
Heat waves now occur three times as often as they did in the 1960s — on average at least six times a year in the United States in the 2010s. Record-breaking hot months are occurring five times more often than would be expected without global warming. And heat waves have become larger, affecting 25 percent more land area in the Northern Hemisphere than they did in 1980; including ocean areas, heat waves grew 50 percent.
These changes matter because extreme heat is the deadliest form of extreme weather in the United States, causing more deaths on average than hurricanes and floods, combined, over the past 30 years. Recent research projects that heat stress will triple in the Pacific Northwest by 2100 unless aggressive action is taken to reduce heat-trapping greenhouse gas emissions.
Some still refuse to acknowledge the dire warning that Mother Nature is sending us. They say the science is too unsettled to take action. But uncertainty, if anything, is a reason for taking even more dramatic action to reduce carbon emissions. Uncertainty is not our friend. And the current heat dome is an excellent example of why.
The heat wave afflicting the Pacific Northwest is characterized by what is known as an omega block pattern, because of the shape the sharply curving jet stream makes, like the Greek letter omega (Ω). This omega curve is part of a pattern of pronounced north-south wiggles made by the jet stream as it traverses the Northern Hemisphere. It is an example of a phenomenon known as wave resonance, which scientists (including one of us) have shown is increasingly favored by the dramatic warming of the Arctic.
By decreasing the contrast in temperature between the cold pole and warm subtropics, the amplified warming of the Arctic causes the jet stream to slow down and, under the right circumstances, like the ones prevailing now, settle into a very wiggly and rather stable configuration. That, in turn, allows very deep high pressure centers, like the current heat dome, to remain locked in place over a region, as it is over the Pacific Northwest.
Those climate models that the critics claim are alarmist do a poor job of reproducing this phenomenon. That means that the models do not account for this critical factor behind many of the persistent and damaging weather extremes we’ve seen in recent years, including the heat dome.
But there is a way out of this nightmare of ever-worsening weather extremes, and it’s one that will serve us well in many other ways, too. A rapid transition to clean energy can stabilize the climate, improve our health, provide good-paying jobs, grow the economy and ensure our children’s future. The choice is ours.
Michael E. Mann is a professor of atmospheric science, the director of the Earth System Science Center at Penn State University and the author of “The New Climate War: The Fight to Take Back Our Planet.” Susan Joy Hassol is the director of the nonprofit organization Climate Communication. She publishes the series “Quick Facts” with the American Association for the Advancement of Science’s SciLine on the connections between extreme weather and climate change.
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