North America has been experiencing unusual weather of late. After a mild winter over much of the continent, last week it experienced record-breaking summer-like conditions. In Canada, for instance, the thermometer in St John鈥檚, New Brunswick, hit 25.4 掳C on 21 March, smashing the previous record high for March of 17.5 掳C.
鈥淲e鈥檝e never seen these kinds of temperatures before. It鈥檚 quite remarkable,鈥� Dave Phillips, a senior climatologist at , a government agency, .
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鈥淭he duration, areal size, and intensity of the 鈥榮ummer in March鈥� heat wave are simply off-scale,鈥� says of the Weather Underground. 鈥淭he event ranks as one of North America鈥檚 most extraordinary weather events in recorded history.鈥� 快猫短视频 takes a closer look.
The 鈥渟ummer in March鈥� has now come to an end but what caused it?
Meteorologists have been pointing to two main factors. First, , there was a big loop in the jet stream over the continent, funnelling warm air northwards from the Gulf of Mexico. This loop in the jet stream remained 鈥渟tuck鈥� in place for over a week, a phenomenon known as a blocking pattern.
And the second factor?
Phillips points out that air flowing northwards in the spring would normally be cooled as it passes over cold, snowy ground. But this year there is very little snow because of the mild winter and the air was hardly cooled at all.
So is there a link with global warming?
There may be. 鈥淕lobal warming boosts the probability of really extreme events, like the recent US heat wave, far more than it boosts more moderate events,鈥� point out climate scientists Stefan Rahmstorf and Dim Coumou in .
How could global warming have produced an off-the-charts event like the 鈥渟ummer in March鈥�?
Nobody can say for sure, but we can speculate. First, sea-surface temperatures in the Gulf of Mexico have been higher than normal in the past couple of months, , which means the air that flowed north would have been warmer to start with. That .
There is also some evidence that , at least in the western US.
Global warming may also have influenced the jet stream pattern. According to research published last week by Jennifer Francis of Rutgers University (), the rapid warming in the Arctic is affecting atmospheric circulation further south, making weather patterns more persistent 鈥� more blocking, in other words 鈥� which makes some kinds of extreme weather, such as heatwaves, more likely.
So several different factors, each made more likely by global warming, combined to produce this very extreme event?
Possibly. 鈥淚 think [that is] right but it is hard to prove,鈥� said Kevin Trenberth of the US National Center for Atmospheric Research, when 快猫短视频 asked him about this. Masters, meanwhile, described the idea as 鈥渆ntirely plausible鈥�.
Does this mean more extremely warm springs are likely?
Not necessarily. The confluence of events that caused the 鈥渟ummer in March鈥� might still be exceedingly rare, even if the odds of such an event occurring are much higher than before. Again, nobody really knows. Masters says more detailed climate models are needed to track synergistic effects and anticipate extreme events such as this. However, the 鈥渟ummer in March鈥� is cause for concern.
In 2004, Paul Epstein of Harvard Medical School鈥檚 Centre for Health and the Global Environment, and James McCarthy of Harvard University, : 鈥淲e are already observing signs of instability within the climate system [鈥 there is no assurance that the rate of greenhouse gas build up will not force the system to oscillate erratically and yield significant and punishing surprises.鈥�
As Masters notes, significant and punishing surprises are exactly what we have been seeing in the US and elsewhere recently. And if such an 鈥渙ff the chart鈥� event can occur when the world has warmed by less than 1 掳C, what sort of extreme events will occur by 2050, ?
