I've been planning to write about this for ages, but hibernation and life in general always get in the way. Never mind the fact that it's a complex subject, surrounded on all sides by uncertainty. But why burden yourself with a (seemingly) herculean task, when others have already written about it so eloquently, and explained it so well?
WACC stands for Warm Arctic Cold Contintents, and refers to blocking patterns that cause outbursts of cold air to spill out from the Arctic and cause extreme winter conditions further down on the Northern Hemisphere (image on the right found here). The theory is that these blocking patterns are in turn caused by a breakdown in the Polar Vortex, due to a combination of Arctic amplification, autumnal snow cover increase and sea ice retreat (particularly in the Barentsz and Kara Sea).
Here are some research papers on the subject, the most recent of which received quite a bit of media attention in the past few months:
- Budikova, 2008, "Role of Arctic sea ice in global atmospheric circulation: A review." PDF
- Francis et al., 2009, "Winter Northern Hemisphere weather patterns remember summer Arctic sea-ice extent." PDF
- Overland and Wang, 2010, "Large-scale atmospheric circulation changes are associated with the recent loss of Arctic sea ice." PDF
- Petoukhov and Semenov, 2010, "A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents." PDF
- Overland et al., 2011, "Warm Arctic–cold continents: Impacts of the newly open Arctic Sea." PDF
- Cohen et al., 2012, "Arctic warming, increasing snow cover and widespread boreal winter cooling." PDF
- Jaiser et al., 2012, "Impact of sea ice cover changes on the Northern Hemisphere atmospheric winter circulation." PDF
Most or all of these papers will at one point be included in the paper subsection for Atmospheric patterns.
Some excellent articles have recently come out, explaining this seemingly new phenomenon. Chris R has a whole series of posts on the subject on his Dosbat blog. Last week professor Jennifer Francis wrote an excellent article for Yale Environment 360: Linking Weird Winter to a Rapid Warming of the Arctic. And over at Skeptical Science, John Mason had another great post related to the Arctic: Declining Arctic sea-ice and record U.S. and European snowfalls: are they linked?
Nobody really knows what the exact consequences of these interlinked atmospheric phenomena will be, but I think a lot more will be found out in the next 5 years, as it looks like the causes behind WACC will get worse: the Arctic getting warmer, sea ice retreating more in summer and reforming later in fall, snow cover increasing in fall, followed by a rapid reduction in spring.
So, we'll soon find out. For better or for worse. Probably not better...