How Climate Change May Affect Winter "Weather Whiplash"

Nature

There’s nothing like a wave of wacky weather to spark discussions about climate change.

In the last few weeks, temperatures in the Midwest and Northeast have swung wildly from bone-chilling cold to unseasonably warm, in some places jumping more than 50 degrees Fahrenheit in the span of just a few days.

It’s a case of “weather whiplash”—a sudden shift from one set of weather conditions to another. And now, experts are questioning whether the changing climate may affect some kinds of winter whiplash events.

The answer, as with most questions related to global warming: It’s complicated. But there may be some links.

In recent years, scientists have proposed that climate change may drive an increase in weather whiplash in some parts of the United States. But studies have rarely focused specifically on winter weather. They’ve often focused mainly on precipitation, either during the growing season or on year-to-year time scales.

One 2018 paper, for instance, suggests that California will see an increase in both extremely wet and extremely dry weather. As a result, the state will experience an increase in the frequency with which an extremely wet year follows an extremely dry one.

“I think, in general, the impacts of changing winters are less understood than growing season, and so this is another example of that,” said Alix Contosta, an environmental scientist at the University of New Hampshire.

Contosta, along with hydrologist and biogeochemist Nora Casson of the University of Winnipeg, has been investigating the effects of winter weather whiplash in a project funded by the National Socio-Environmental Synthesis Center. So far, they’ve been examining data from the Hubbard Brook Ecosystem Study, a long-term monitoring program in the White Mountains of New Hampshire. They’ve looked at the relationship between whiplash events and the local hydrology, and how these events may affect water flow and flooding risks.

For now, there’s no formal scientific definition of a weather whiplash event.

It’s been loosely defined as a kind of “collision of circumstances where you have a swing in weather that is out of alignment with what would be considered ‘normal,’ or what is considered ‘expected,’” according to Contosta.

More generally, meteorologists and media reports have often referred to rapid shifts from one type of weather to another—warm to cold or wet to dry—as “whiplash.”

Scientists say these kinds of events can have major implications for human societies, which makes them important to study. Rapid shifts from freezing to thawing conditions, for instance, can raise the risk of bursting pipes, sudden floods from melting snow and ice, or other infrastructure damage. They can also confuse or disrupt plant growth and threaten agricultural yields.

There may be a few ways that climate change could affect the likelihood of short-term whiplash events during the wintertime, experts say.

Meteorologists have attributed the recent surge of subfreezing temperatures to a temporary shift in the polar vortex, a swirling mass of air that circles over the Arctic. That shift sent a blast of icy polar air streaming down over eastern North America. And, as numerous reports have pointed out in the last week or two, some scientists suggest that changes in the behavior of the polar vortex might be driven—at least in part—by warming in the Arctic, where temperatures are currently rising at about twice the global average rate.

It’s an emerging field of science, and one that climate scientists are still heavily debating. While research does suggest the polar vortex may be shifting its position more frequently in recent years—and these shifts often seem to occur around the same time as warm spells or heat waves in the Arctic—models have generally been unable to establish a causal link between the two. As a result, some scientists believe that other factors must be at play.

Still, if the theory is correct, it could mean more frequent midwinter Arctic blasts, even as temperatures overall are on the rise. That could potentially cause an increase in the kind of seesawing conditions that occurred in these last few weeks.

Between background climate warming, heat waves and the cold bursts from the polar vortex, “we have kind of this tug of war, kind of offsetting or conflicting factors or forcings, that’s leading to this volatility in the weather,” said Judah Cohen, a climatologist and director of seasonal forecasting at the analytics firm Atmospheric and Environmental Research. He’s one of the researchers who have suggested there may be a link between Arctic warming and the behavior of the polar vortex.

Uncertain effects of climate change

For now, whatever the causes, temperature fluctuations may be on the rise. Cohen published a paper in 2016 finding that variability in winter temperatures has increased across the Northern Hemisphere’s middle latitude regions in recent years.

It’s a finding that would seem “contrary to expectations,” Cohen writes, as modeling studies generally predict that temperature variability, or the extent to which temperatures tend to fluctuate up and down, should actually decline worldwide in a warming world.

And on a global scale, across all seasons, this seems to be the case—or, at least, variability isn’t increasing. At least one study has suggested that average global temperature variability has remained fairly flat over the last few decades.

But the study points out that zooming into specific regions may yield different results. In parts of Europe and North America, for instance, variability does seem to be increasing.

What will happen in these regions in the coming decades, though, remains in question.

For his part, Cohen suggests that temperature-related winter whiplash events will increase, at least in the short term. Because models don’t capture links between Arctic warming and the polar vortex, he says their projections about future temperature variations may still need some tweaking.

Still, the drivers of the polar vortex remain under debate. And if these swings in its position taper off or fail to increase in the future, winter temperature fluctuations may become less common, or at least less dramatic, as the models predict.

In many locations, including across the United States, winters are still warming faster than summers, and the coldest temperatures are heating up. In general, the difference between the coldest extremes and the hottest extremes is expected to narrow as everything warms across the board.

On the other hand, models suggest that precipitation patterns should become more variable across most of the world as the climate warms—in other words, there should be more fluctuations between wet and dry conditions. A 2017 study in Scientific Reports notes that day-to-day variations in precipitation patterns have already increased over the last few decades and that variability may continue to increase by up to 5 percent for every degree Celsius the climate warms.

Not only are precipitation patterns shifting more frequently from wet to dry, but precipitation events are becoming more intense in many places, as well. In the winter, that could mean more pronounced shifts between dry conditions and intense rainstorms or snowstorms.

False springs

There are other forms of winter “whiplash” that may be influenced by climate change, including the transitions from fall to winter and from winter to spring. But these effects are also complicated and may vary from one place to the next.

Numerous studies have suggested that the timing of the seasons is changing across the United States as the climate warms. Fall is lasting longer, and spring is coming earlier. That may mean a greater likelihood of sudden or uneven shifts between growing-season weather and winter weather.

In some places, research shows that the timing between the last frost of the season and the onset of new plant growth is starting to wobble out of sync. Plants are beginning to emerge too early, tricked by rising temperatures, and they’re getting frozen by late-season cold snaps in a phenomenon scientists refer to as a “false spring.”

A particularly disastrous false spring occurred across much of the United States in 2012—the earliest one in North American records, research later concluded—leaving the newly budding plants vulnerable to late-season freezes.

The results were devastating. In Michigan, for example, unseasonably warm temperatures brought the state’s apple orchards into bloom several weeks too early, exposing them to a spate of deep-freeze events later in the season. Fruit growers lost millions of bushels of apples amounting to about half a billion dollars in damages, prompting then-Gov. Rick Snyder (R) to request disaster assistance from the U.S. Department of Agriculture.

These kinds of events may be on the rise over the long term in some places. One 2013 study in Illinois, for instance, found that the likelihood of plants experiencing frost damage had grown significantly in the last few decades, compared to the risk a hundred years ago. The study attributed the findings to “the combination of warming trends and temperature variability (extremes) associated with climate change” altering the timing of spring plant growth.

But this effect isn’t necessarily increasing everywhere. One 2014 study found that false springs will increase in some places in the United States and decrease in others. On the whole, though, more places are seeing declines, as the date of the last frost is actually shifting even earlier than the onset of the spring “green-up.” The biggest region where false springs seem to be actually increasing is in the intermountain western United States, the area between the Rockies and the Sierras.

Across the board, whether winter whiplash events increase or decrease with global warming seems to depend on the exact type of event, the location and, in some cases, the influence of certain climate factors that scientists are still investigating. Continuing to monitor and investigate these links may help communities better prepare for extreme weather in the future.

In October 2011, for instance, a powerful nor’easter brought a surge of unusually early snowfall to the Northeast in an event popularly nicknamed “Snowtober.” The event caused millions of power outages throughout the region as snow blanketed the branches of trees that had not yet lost their leaves, weighing them down and causing them to topple over onto nearby power lines.

“You can see that states and other jurisdictions recognized the impacts of those kinds of events, and there were a bunch of policy changes that came in following the early snowstorms having to do with how far back you have to cut [tree branches] from power lines,” said Casson, the University of Winnipeg scientist.

“So there is some evidence that communities and other jurisdictions can adapt.”

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.

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