Is Summer Climate Shift Happening Sooner Than Forecast?

[bluewave]

An new study came out in 2013 which forecast a late 21st Century summer climate shift. This new summer pattern features  a cooler trough over portions of the Arctic and a ring of 500 mb blocking further to the south. This type of Northern Hemisphere circulation regime occurred in 2013 and again in 2018. It may too soon to tell if this an earlier beginning to what  the climate model was showing. But it's interesting how closely the 500 mb patterns during these recent summers resemble the late 21st Century forecast.

Climate model forecast

 

Recent summer 500 mb patterns

 

 

Link to study:

http://adsabs.harvard.edu/abs/2013AGUFM.A43C0270V

The Role of the Arctic in Promoting Drought and Heat Waves over Mid-latitude Continents

Vavrus, S. J.; Francis, J. A.

American Geophysical Union, Fall Meeting 2013, abstract id. A43C-0270

Climate models typically simulate enhanced heating and pronounced drying during summer over mid-latitude continental regions of the Northern Hemisphere under greenhouse forcing. Various plausible explanations have been offered for this response, including strengthened land-sea temperature contrasts, favorable SST patterns, and locally depleted soil moisture. Changes in the large-scale atmospheric circulation have also been proposed, but these have generally been regarded as secondary mechanisms originating in low and middle latitudes. Here we present an alternative perspective, by proposing that a major reason for the mid-latitude continental response is an atmospheric circulation change that is regulated by high-latitude processes. Based on an analysis of the RCP8.5 scenario in the Community Climate System Model (CCSM4), we find that the amplified heating ( > 7 K) and drying ( > 20%) of the U. S. Great Plains during summer stems from a shift toward locally weakened westerlies aloft and somewhat stronger northerlies. This circulation change is directly tied to enhanced ridging to the north of the region that is part of a nearly hemispheric-wide band of ridging in high latitudes extending from Eurasia across North America. This band of maximum geopotential height increases aloft is well correlated with the location of greatest summertime snow cover loss in northern Siberia and North America. The circulation pattern appears to be further modulated in high latitudes by residual sea ice coverage around the Canadian Archipelago and by a weakening of the Atlantic Meridional Overturning Circulation. Both of these changes promote troughing locally around northeastern Canada and thus a southward displacement over North America of the high-latitude ridging band to a location where its outflow favors drier and hotter conditions in the continental interior. The resulting circulation shift affects not only the mean summertime climate but also sets up very suitable synoptic conditions for extreme weather events in the form ofdroughts and heat waves.

 

 

 

[etudiant]

A provocative paper, suggesting circulation change drivers are 'residual sea ice coverage around the Canadian Archipelago and by a weakening of the Atlantic Meridional Overturning Circulation'.

Are these driving elements changing in a measurable way? 

[bluewave]

3 hours ago, etudiant said:

A provocative paper, suggesting circulation change drivers are 'residual sea ice coverage around the Canadian Archipelago and by a weakening of the Atlantic Meridional Overturning Circulation'.

Are these driving elements changing in a measurable way? 

Real Climate has the most recent information on the weakening AMOC.

http://www.realclimate.org/index.php/archives/2018/05/if-you-doubt-that-the-amoc-has-weakened-read-this/

[etudiant]

Thank you, a very good paper and an easy read.

[AfewUniversesBelowNormal]

Yeah, that's pretty crazy. There is no reason for the +NAO as far as I can tell. 

[bluewave]

11 hours ago, AfewUniversesBelowNormal said:

Yeah, that's pretty crazy. There is no reason for the +NAO as far as I can tell. 

It's a different type of summer +NAO pattern than we saw in the past. The very strong ring of 500 mb blocking across most of the Northern Hemisphere to the south is something new. Notice how much weaker the ridging was in the 50's to 90's +NAO summers.This type of pattern first showed up in 2006.

[ma blizzard]

9 hours ago, bluewave said:

It's a different type of summer +NAO pattern than we saw in the past. The very strong ring of 500 mb blocking across most of the Northern Hemisphere to the south is something new. Notice how much weaker the ridging was in the 50's to 90's +NAO summers.This type of pattern first showed up in 2006.

 

 

 

 

I wonder how the 50s composite would look if it were in relation to the 30 year period relative to that decade