Sweltering Summers Linked to Rapidly Warming Arctic
Wildfires are ravaging California, and heat waves are scorching Europe as extreme weather takes hold around the world this summer.
Those blazes and hot spells might be worse because of high temperatures in the icy Arctic, new research shows.
Scientists have long pointed to the clear fingerprint of human-caused warming on many of these events, suggesting that as global temperatures continue to rise, extreme heat, wildfires and other climate-related disasters will worsen.
Climate change may be influencing extreme summer weather in some less obvious ways, too. A new study finds that rapid warming in the Arctic—where temperatures are currently rising faster than anywhere else on Earth—may be altering certain summertime atmospheric circulation patterns in ways that affect the weather in North America, Europe and other midlatitude regions.
A new review paper, published today in the journal Nature Communications, examines a wide range of research on some of the suggested links between Arctic warming and summer weather. Though many questions remain, the paper finds that some connections likely do exist.
“Summers of course are getting hotter, not just by simple warming due to global warming, but on top of that you can have these dynamical changes in the jet streams, which can lead to very persistent, very intense extremes,” said lead study author Dim Coumou, an expert on atmospheric circulation and extreme weather at the Potsdam Institute for Climate Impact Research in Germany.
In recent years, possible links between Arctic climate change and midlatitude weather patterns have gained interest from climate scientists. Generally, the idea is that amplified Arctic warming alters the overall difference in temperature, or the temperature “gradient,” between the Arctic and the lower latitudes. This gradient influences a number of properties, including the thickness of the atmosphere in any given location and the way that air flows around the planet.
A great deal of research has focused on the links between Arctic warming and winter weather patterns. The authors of the new study note that “a scientific consensus is emerging that [Arctic amplification] has at least some influence on winter weather.”
Research on the links to summer weather has received somewhat less attention—but interest may be growing. Because of the ongoing background influence of global warming, extreme heat events and related disasters like droughts and wildfires are on the rise in many places. If Arctic changes, specifically, have the potential to influence global weather patterns even further, it could lead to more severe or unexpected events.
In particular, researchers have begun to suggest that Arctic-influenced changes in summer circulation patterns can cause weather systems in certain parts of the world to get “stuck,” or to persist for abnormally long periods of time—sometimes with devastating consequences. Long periods of hot, dry weather can lead to extreme heat waves, droughts or wildfires, for instance, while long-lasting rainfall leads to floods. But the exact mechanisms driving these persistent weather patterns—and any potential links to Arctic warming—remain a subject of debate.
3 theories
This new review is among the first to analyze the existing literature on Arctic warming and summertime circulation. It evaluates three hypotheses about the links between Arctic warming and midlatitude summer weather.
One theory suggests that it could weaken certain eastward-blowing winds and inhibit weather activity in the midlatitude “storm tracks”—the parts of the ocean where weather systems typically form and move across the globe. Weakenings in these patterns could allow hot, dry weather conditions to build up and persist over the surrounding continents.
Another theory: Arctic warming could cause the jet stream—which has a major influence on global weather patterns—to shift southward.
A third hypothesis suggests that changes in the temperature gradient could cause an increase in certain types of atmospheric waves, causing large air flow patterns like the jet stream to meander up and down as they travel around the world. This could lead to an increase in atmospheric blocking patterns, or weather patterns that stall in one place for an extended period of time.
The researchers note that an occasional natural phenomenon known as a “double jet stream” can also cause a temporary increase in waves and summer blocking patterns. This is when the jet stream actually splits into two flowing rivers of air instead of just one.
While double jets typically form only once every few years or so, summer warming over Arctic land masses may increase their likelihood, the researchers note.
The review finds that there’s substantial evidence for an effect on midlatitude storm tracks. Observations suggest that a weakening effect has already occurred over the past few decades, the paper notes, and modeling studies support the idea that it’s influenced partly by amplified Arctic warming.
The theories involving the jet stream shift and the changes in the temperature gradient carry more uncertainty in the research, but some links may still exist.
World of extremes
The exact links to Arctic climate change may still be up for debate, but it’s clear that persistent weather patterns in the midlatitudes can have extreme consequences. Record-breaking wildfires in recent years may be a prime example.
A separate paper published today in the journal Scientific Reports suggests that the massive 2016 Fort McMurray wildfire in Alberta—Canada’s costliest disaster on record—was likely linked to a persistent planetary wave pattern existing in the Northern Hemisphere at that time. This wave pattern helped drive a high-pressure system over western Canada that favored unusually hot, dry conditions for the region. The weather was worsened by the effects of a particularly severe El Niño event, which was still in full swing at the time.
The new paper suggests that the same wave structure could have helped drive the conditions fueling other wildfires that cropped up across the Northern Hemisphere in 2016, although it doesn’t specifically investigate those links. It also suggests that a similar planetary wave structure could have influenced an unusual spate of wildfires in Greenland last summer.
Mike Flannigan, a wildfire expert at the University of Alberta, said in a recent conversation with E&E News that some researchers are concerned about future increases in blocking patterns over western North America, which has seen some of its most intense wildfires on record in the last few years.
Flannigan pointed to recent research, including a 2017 paper in Scientific Reports, suggesting Arctic-driven changes in the jet stream could increase the frequency of atmospheric blocking and extreme weather events.
Many of the extreme heat waves that have dominated European news the last few summer have been associated with stationary weather patterns, as well, said climatologist Judah Cohen, director of seasonal forecasting at the analytics group Atmospheric and Environmental Research.
“We’ve had quite a few summers that you can rattle off that we’ve had this extreme heat—for them, anyway—and seems to be associated with very persistent high-pressure blocks,” he told E&E.
This summer is no exception. According to a recent blog post from the World Meteorological Organization, extreme heat in northern Europe the last few months is linked to a stationary high-pressure system.
As 2018 follows in the footsteps of other recent summers—marked by record-breaking heat events, raging wildfires and other disasters—there’s a growing importance attached to research on extreme summer weather. It’s clear that the global influence of climate change is driving more extremes around the world and will continue to do so.
Still, the influence of Arctic warming—especially in the summer—remains a controversial subject among some climate scientists. Not all experts agree on the strength, or even the existence, of all the links that have been suggested in recent years.
And some researchers suggest that climate change in other parts of the world, such as the tropics, likely has a greater influence on the midlatitudes, even if Arctic warming does play some role. The new review points out that there are likely other influences coming from other parts of the world, some of which may actually interact with any atmospheric changes driven by the Arctic climate.
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.