Increasing Greenland Summer Blocking Linked To Decreasing Spring North American Snow Cover

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Research Links Climate Change to Lazier Jet Stream, Leading to Extreme Weather

BY COLUMBIA CLIMATE SCHOOL |JULY 14, 2023

 

 Comments

Jet streams are relatively narrow bands of strong wind in the upper atmosphere, typically occurring around 30,000 feet, and blowing west to east. Their normal flows lead to week-to-week weather variations, modulated in the mid-latitudes by ridges and troughs in the jet stream. A high-pressure ridge, for example, produces clear, warmer weather conditions; a trough is typically followed by stormy conditions. Together, these form waves in the jet stream that can stall as the waves grow and become more amplified, causing “stuck” weather patterns that produce longer storms and heat waves.

New research published in Nature Communications describes observations linking increased warming at high latitudes and the ever-decreasing snow cover in North America to these stalls in atmospheric circulation.

“These persistent and extreme conditions are thought to be increasing in the future as a result of this increased waviness in the jet stream.” said the study’s lead author Jonathon Preece, a postdoctoral researcher at the University of Georgia.

High-pressure ridge over Texas, 2018. (Weatherbell)

Since 2000, frequent “stuck” weather patterns have produced heat waves over Greenland, resulting in exceptional melting of the Greenland Ice Sheet. In contrast to these observations, global climate models actually project a slight decrease in the blocked patterns over Greenland and, consequently, the models have underrepresented the contribution of meltwater runoff from the ice sheet to global sea level rise.

“These patterns have been consistently creating pulses of melting over the Greenland ice sheet that have been accounting for a large portion of the annual melting,” said study coauthor Marco Tedesco, a professor at Columbia Climate School’s Lamont-Doherty Earth Observatory, and lead principal investigator on the project. “Accounting for such an aspect is crucial for anticipating not only how much but how fast Greenland is and will be contributing to sea level rise.”

“One question is whether this is a consequence of climate change that we can expect to continue in the future [that] the climate models are failing to resolve,” said Preece. “Or are the climate models correct, in which case we’d expect things to revert back to the norm and perhaps the rate of accelerated melt of the ice sheet will taper some?”

The new study presents evidence of a link to climate change, both in the increases in jet-stream waviness and ever-decreasing spring North American snow cover extent,  which “is impacting the atmosphere in a way that is favoring these blocked high-pressure systems over Greenland,” Preece said.

Multiple studies have highlighted the discrepancy between climate models and observations. This study provides evidence of a direct connection between the observed shift in summer atmospheric circulation over Greenland and amplified warming at high latitudes.

“The new study is the first that we know of that demonstrates a direct link between the observed change in summer atmospheric circulation over Greenland and diminished spring snow cover, which is something we can confidently say is a consequence of climate change,” said coauthor Thomas Mote, a geographer at the University of Georgia.

Adapted from a press release by the University of Georgia.

 

Full paper available online with no paywall.
 

https://www.nature.com/articles/s41467-023-39466-6

 

 

Abstract

The exceptional atmospheric conditions that have accelerated Greenland Ice Sheet mass loss in recent decades have been repeatedly recognized as a possible dynamical response to Arctic amplification. Here, we present evidence of two potentially synergistic mechanisms linking high-latitude warming to the observed increase in Greenland blocking. Consistent with a prominent hypothesis associating Arctic amplification and persistent weather extremes, we show that the summer atmospheric circulation over the North Atlantic has become wavier and link this wavier flow to more prevalent Greenland blocking. While a concomitant decline in terrestrial snow cover has likely contributed to this mechanism by further amplifying warming at high latitudes, we also show that there is a direct stationary Rossby wave response to low spring North American snow cover that enforces an anomalous anticyclone over Greenland, thus helping to anchor the ridge over Greenland in this wavier atmospheric state.

 

Interesting timing with this new study. North America just experienced the lowest May spring snow  on record this year. 
 

https://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=namgnld&ui_month=5

The historic spring blocking which greatly reduced the North American snow cover during May could have lead to the extreme blocking and historic SST warmth south of Greenland in July.

 

Which also produced the strong Greenland melt conditions this summer

 

 

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New July record for 500 mb blocking near Southern Greenland.

 

 

[chubbs]

Another Greenland blocking event forecast for this week. Could produce an unusually strong late-season melt event.

 

[chubbs]

 

[Typhoon Tip]

14 hours ago, chubbs said:

 

Heat wave released … a week later boom

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[GaWx]

 Whereas winter -NAOs have been much less frequent in recent decades than they had been, summer -NAOs have done the opposite and have increased markedly.

% of summer months with NAO<0: increased

1950-97:

June: 50%
July: 42%
Aug: 46%
 

1998-2023

June: 73%
July: 65%
Aug: 73%

% of winter months with NAO<0: decreased

 1950-97:

 Dec: 42%
 Jan: 48%
 Feb: 46%
 

1998-2022/3:

Dec: 36%
Jan: 20%
Feb: 27%

 So, whereas summer and winter -NAO month frequencies were about the same during 1950-97, summer -NAO months since 1998 have been 2.5 times as frequent as winter -NAO months!
 

Thus, having a summer -NAO (at least based on recent decades) doesn't at all increase the chance for a subsequent winter's -NAO.

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.nao.monthly.b5001.current.ascii.table

[bluewave]

1 hour ago, GaWx said:

 Whereas winter -NAOs have been much less frequent in recent decades than they had been, summer -NAOs have done the opposite and have increased markedly.

% of summer months with NAO<0: increased

1950-97:

June: 50%
July: 42%
Aug: 46%
 

1998-2023

June: 73%
July: 65%
Aug: 73%

% of winter months with NAO<0: decreased

 1950-97:

 Dec: 42%
 Jan: 48%
 Feb: 46%
 

1998-2022/3:

Dec: 36%
Jan: 20%
Feb: 27%

 So, whereas summer and winter -NAO month frequencies were about the same during 1950-97, summer -NAO months since 1998 have been 2.5 times as frequent as winter -NAO months!
 

Thus, having a summer -NAO (at least based on recent decades) doesn't at all increase the chance for a subsequent winter's -NAO.

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.nao.monthly.b5001.current.ascii.table

Yeah, the summer has seen increasing blocking which may be linked to the decreasing late spring snow cover in North America according to the paper. While winter has seen a decline, we have had some of the best winters for Greenland blocking since 2009 along with some of the lowest blocking seasons. So a much higher range.