Rapidly Warming Winters At Least As Destructive As Record Heatwaves, Expansive Droughts -
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While the popular imagination might associate the climate crisis with scorching summers and their attendant droughts, wildfires, hurricanes and heat waves, milder winters can also be drivers of catastrophic weather events and profound changes. They range from shifts in agricultural use, triggering changing weather patterns to boosting the likelihood of violent events, like the swarm of tornadoes that wreaked havoc in the American midwest and south over last weekend. “One of the truisms in climate science is that cold places and cold times of year warm faster than the warmer places and warmer times of year,” says Daniel Swain, a climate scientist at UCLA studying how extreme events are changing on a warming Earth. “Not only is the actual rate of warming faster in colder seasons and places – like the Arctic, which is warming three times faster than other places – but also a lot of impacts that are associated with warming are amplified.”
Swain points to one specific threshold where temperature has a huge impact: whether precipitation falls as liquid rain or frozen snow depends on just a single degree difference. And in the west of America, where there was a gigantic snow drought until just a few days ago, that has huge impacts. “There was wildfire risk up until last week, even at 8-9,000ft in elevation,” says Swain. “That has directly to do with the lack of snowpack.”
When precipitation falls as snow, it sticks around for longer, creating runoff moisture for the spring season – it’s often referred to as the bank of future water for moisture-strapped places. But when it falls as rain, it runs off immediately. “Winter warming affects the frozenness – or not – of things, which is ecologically important for the accumulation of snowpack and the water supply,” explains Swain.
Warm spells in winter can create extreme heat waves later in summer. Unseasonal warmth can lead to a premature snow melt and vegetation growth, which lowers soil moisture and amplifies the likelihood of extreme and persistent heat waves throughout the summer, says Kornhuber. He points to the chain of events that led up to a heatwave that rocked Siberia in 2020 and was associated with wildfires that lasted the whole summer and caused record breaking carbon emissions. In that event, late-winter heat in February and March sucked moisture from the soils at a time when vegetation was also taking up moisture – and parched soils can lead to summer heat waves, says Kornhuber. “Low soil moisture is one of the most important ingredients of mega heatwaves.”
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https://www.theguardian.com/environment/2021/dec/17/warmer-winters-climate-crisis-scientists