Summer weather is getting 'stuck' due to Arctic warming

["Dave Farber" <farber () gmail com>]

Begin forwarded message:

> From: Dewayne Hendricks <dewayne () warpspeed com>
> Date: August 20, 2018 at 5:05:04 AM PDT
> To: Multiple recipients of Dewayne-Net <dewayne-net () warpspeed com>
> Subject: [Dewayne-Net] Summer weather is getting 'stuck' due to Arctic warming
> Reply-To: dewayne-net () warpspeed com
>
> Summer weather is getting 'stuck' due to Arctic warming
> Rising arctic temperatures mean we face a future of ‘extreme extremes’ where sunny days become heatwaves and rain 
> becomes floods, study says
> By Jonathan Watts
> Aug 20 2018
> <https://www.theguardian.com/environment/2018/aug/20/summer-weather-is-getting-stuck-due-to-arctic-warming>
>
> Summer weather patterns are increasingly likely to stall in Europe, North America and parts of Asia, according to a 
> new climate study that explains why Arctic warming is making heatwaves elsewhere more persistent and dangerous. 
>
> Rising temperatures in the Arctic have slowed the circulation of the jet stream and other giant planetary winds, says 
> the paper, which means high and low pressure fronts are getting stuck and weather is less able to moderate itself.
>
> The authors of the research, published in Nature Communications on Monday, warn this could lead to “very extreme 
> extremes”, which occur when abnormally high temperatures linger for an unusually prolonged period, turning sunny days 
> into heat waves, tinder-dry conditions into wildfires, and rains into floods.
>
> “This summer was where we saw a very strong intensity of heatwaves. It’ll continue and that’s very worrying, 
> especially in the mid-latitudes: the EU, US, Russia and China,” said one of the coauthors, Dim Coumou from the 
> Potsdam Institute for Climate Impact Research. “Short-term heatwaves are quite pleasant, but longer term they will 
> have an impact on society. It’ll have an affect on agricultural production. Harvests are already down this year for 
> many products. Heatwaves can also have a devastating impact on human health.”
>
> Circulation stalling has long been a concern of climate scientists, though most previous studies have looked at 
> winter patterns. The new paper reviews research on summer trends, where it says there is mounting evidence of 
> planetary wind systems – both low-level storm tracks and higher waves in the troposphere – losing their ability to 
> shift the weather.
>
> One cause is a weakening of the temperature gradient between the Arctic and Equator as a result of man-made 
> greenhouse gas emissions. The far north of the Earth is warming two to four times faster than the global average, 
> says the paper, which means there is a declining temperature gap with the central belt of the planet. As this ramp 
> flattens, winds struggle to build up sufficient energy and speed to push around pressure systems in the area between 
> them.
>
> As a result, there is less relief in the form of mild and wet air from the sea when temperatures accumulate on land, 
> and less relief from the land when storms build up in the ocean. Last year, Hurricane Harvey had a devastating impact 
> on Texas because it was parked an unusually long time on the coast, where it kept drawing up moisture from the sea 
> and dumping it in the form of the greatest deluge ever recorded in the US. Scientists had previously noted that 
> hurricanes are slowing and bringing more rain.
>
> A separate new paper in Scientific Reports indicated that the trapping of planetary airstreams – a phenomenon known 
> as amplified quasi-stationary waves – also contributed to the 2016 wildfires in Alberta, which took two months to 
> extinguish and ended as the costliest disaster in Canadian history with total damages reaching 4.7bn Canadian dollars.
>
> “Clearly, the planetary wave pattern wasn’t the only cause for the fire – yet it was an additional important factor 
> triggering a deplorable disaster,” says lead author Vladimir Petoukhov from the Potsdam Institute for Climate Impact 
> Research. “In fact, our analysis reveals that beyond that single event, actually from the 1980s on, planetary waves 
> were a significant factor for wildfire risks in the region.”
>
> He said wave pattern studies will help forest managers and fire forecasters because changes can be detected ahead of 
> their impacts.
>
> However, scientists are also concerned that slowing circulation could produce “surprises”, by amplifying other 
> climate changes.
>
> [snip]
>
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