Thread by @dana1981

So, what's happening in the Arctic now is kinda crazy, but also really important to extreme weather throughout the northern hemisphere. Read my piece today on the topic, but here's a Thread:
yaleclimateconnections.org/2020/10/warmer…

First, the basics: there's a "positive feedback" (positive in the negative sense, Trump would say), like a mutually destructive relationship. Warming melts ice & snow in the Arctic, making the surface less reflective -> absorb more sunlight -> warm more -> melt more -> etc. 1/n

As a result, the Arctic is warming 3x faster than the global avg, and sea ice is disappearing fast. Half Arctic sea ice surface area and 75% of its volume disappeared in summers between 1979 and 2012.

Then 2014–2020 were the 7 hottest years on record. Guess what happened? 2/n

Polar scientists kept expecting a new record summer minimum Arctic sea ice low, but no! There were new record lows in winters and springs, but something kept happening in August/September to preserve some ice and prevent a new summer minimum record. 3/n

The 2012 summer Arctic sea ice minimum record still stands, as this great visualization from @ahaveland illustrates 4/n

So, what the hell? The hell, posit Jennifer Francis and Bingyi Wu in a new paper, is that the melting Arctic snow and ice are disrupting the jet stream, often causing low-pressure cloudy systems to linger in the Arctic in Aug/Sep, keeping temps cool & winds spreading the ice 5/n

But this doesn't happen every year. It didn't happen in 2019 and 2020, which, as you can see in the @ahaveland video above, both nearly broke the summer sea ice minimum record. The melting snow & ice are ironically creating conditions to preserve some summer sea ice, but...6/n

This effect is only enough to temporarily slow the 'Arctic sea ice death spiral.' Global warming is relentless, whereas the summer cloudy Arctic weather systems are sporadic. Another new paper predicted ice-free Arctic summers beginning somewhere between about 2030 and 2050 7/n

So what's up with the jet stream? The temp difference between the Arctic & lower latitudes creates a force that moves it along. Like a river current, air currents tend to go straight when fast & meander when slow. Faster warming in Arctic = less temp diff = slower jet stream 8/n

Slower, wavier jet steam means the air current doesn't move weather systems along, so they tend to get stuck in the jet stream waves. Like the low-pressure cloudy summer Arctic systems, but also high pressure systems in Scandanavia, Canada, etc., creating nasty heatwaves 9/n

Other papers have linked these Arctic-connected wavy jet stream patterns to winter high-pressure ridges off the coast of California, like the one that contributed to the state's worst drought in a millennium in 2012–2016, or the one that caused Europe's deadly 2003 heatwave 10/n

There are lots of other examples in this 2018 study led by @MichaelEMann of these 'quasi-resonant amplification' jet steam wave events being connected to extreme weather events (11/n):
advances.sciencemag.org/content/4/10/e…

There's a fast-growing body of climate science research on these connections between changes in the Arctic, the jet stream, and extreme weather events getting stuck. Hurricanes may even be slowing down & wreaking more havoc as a result, though we need more research on that (12/n)

Anyway, it's all very fascinating stuff. To abuse the cliché, what happens in the Arctic doesn't stay in the Arctic. Now, if you haven't yet, read my article! (13/13)
yaleclimateconnections.org/2020/10/warmer…