I made a mistake. I predicted that this year’s super El Niño would bring heavy January and February rains and flooding to California like they did in the super El Niño years of 1982 and 1998. Good rains have come to the U.S. west coast this winter, but they haven’t persisted because many storms have spun up to Alaska instead of into California and the Pacific northwest. Unless a miracle March brings record rainfall, much of California will remain deep in drought as El Niño fades.
In science, when your best forecast based on good numerical models and decades of experience goes wrong, it’s time to ask why because you might have missed something very important. What I am finding is something very concerning for California’s climate, namely that as sea ice retreats on the Atlantic side of the Arctic ocean so much heat is being released to the Arctic atmosphere that it’s splitting the the polar vortex, at the storm track level — 500 millibars — in two. Much of the rain that would have gone to California is going to Alaska leaving low elevations in the region around Anchorage snow free. The extraordinary increase in the heat content of the north Atlantic ocean has disrupted the atmospheric circulation of the whole northern hemisphere.
When I gave my talk in Asheville, NC in September, 2015 to southeastern Daily Kos activists I knew that the much above normal water temperatures off the east coast would have an effect on this year’s El Niño weather pattern, but I had no historic basis for determining what it would be. The most similar El Niño was likely to be 1997-1998, but the ocean heat in the north Atlantic off the east coast is much higher this year. A number of large changes have happened since then. At present water temperatures south of the Canadian maritime provinces are, perhaps, as much as 15ºF above normal (figure 1on top). Warm eddies have spun off the Gulf stream, in a region that used to have a much larger input of cool water that flowed down from Labrador. Buoy readings verify satellite measurements (which may be affected by prolonged cloudiness) that these waters are much warmer than normal. The warm anomalies in this region are larger than the El Niño anomalies.
Profound changes have taken place in the north Atlantic since 1997. Recent research by Dr. Stephan Rahmsdorf has found evidence of a long-term slow down in deep water formation in the Labrador and Greenland seas. This is commonly referred to as a “Gulf Stream slowdown”. However, from the late 1980’s through 1995, very stormy, cold winters brought renewed intensity to deep water formation. The resurgence of the “global conveyor belt” intensified the flow of warm water up the coast of Norway into the Arctic seas. By the year 2000 sea ice in the Barents sea began to retreat as warm north Atlantic water, which partially originated in the Gulf Stream, pushed into the Arctic. Since 1995, Atlantic deep water formation has slowed, in part, because the melting of glaciers in Greenland and throughout the Arctic, has freshened the waters. Freshened water is lighter than salty water so it slows deep convection.
In 2010 the Gulf Stream, itself, slowed down. Although the Gulf Stream recovered quickly, deep water formation did not. Transport of warm water across 50ºN dropped, and by 2013 the rapid loss if sea ice stopped. September Arctic sea ice extent, area and volume ice all made a large recovery in September 2014. The slowdown led Dr. Stephen Yeager, in 2015, to predict a slowdown in sea ice loss on the Atlantic side of the Arctic in the journal Geophysical Research Letters.
Something happened that Dr. Yeager didn’t expect . The Gulf Stream expanded northwards. The southwards flow of Labrador Current water slowed. The wall of the Gulf Stream moved to the north and warm Gulf Stream eddies replaced the missing cool water. Water off the east cost got much warmer and saltier. Coastal storms intensified (e.g. Sandy).
In winter 2015 the warm water fueled record snow storms in Boston. The storms off the east coast that moved northeastwards built an atmospheric vortex around Greenland. By late February extraordinarily deep lows off the tip of Greenland caused sea surface heights to plummet indicating that deep water formation had strengthened there. Record cold sea surface temperatures in the gyre in the seas off of Labrador and Greenland began to mix through the warm salty layer of Mediterranean water at a depth of 3000 feet (1000 meters). Then the flow of warm water up the coast of Norway into the Arctic sea strengthened.
East coast sea levels are extraordinarily high for winter.
Apparently, the increasing salinity of the subtropical water resulting from the warming and drying of the subtropical and tropical Atlantic has partially canceled out the decreasing salinity of the subpolar waters resulting from glacial melting.
But we have a problem. Either the “Gulf Stream” is strong and warm waters melt away the sea ice of the “Gulf Stream” slows down and the heat builds up in the tropical and subtropical Atlantic. Greenhouse gases have created a large imbalance between the radiation coming in and going out and the excess heat is going into the oceans. The north Atlantic has taken up an extraordinary amount of heat that is intensifying storms and changing atmospheric circulation patterns.
Moreover, the loss of sea ice on the Atlantic side of the Arctic ocean is causing profound changes in atmospheric circulation patterns. Sea ice area in the Barents Sea has plummeted to record lows recently. Note that winter Barents sea ice areas began to drop in the year 2000, precisely when the droughts in California and the western states began. This is not merely coincidental. The dome of warm humid air that develops above that warm Atlantic ocean water acts like a dam in the atmosphere that sends a cold return flow towards eastern Canada. The heat dome tends to break the northern hemisphere’s atmospheric circulation in two.
The shocking heat on the Atlantic side of the Arctic this winter has been discussed in the popular media but its extreme effects on the mid-level polar vortex have not been mentioned as far as I know. An El Niño year generally has stronger westerly winds than an average year so the best year to compare this winter to is 1998. The following figures compare January 1 through February 16 for 1998 and 2016 at the 500 mb level where atmospheric pressure is about half of surface pressure. These maps are good indicators of the atmospheric circulation and storm tracks.
Jan.1 1998 through Feb. 16, 1998 average northern hemisphere circulation pattern at about half of surface pressure, 500mb.
Jan.1, 2016 through Feb. 16, 2016 average northern hemisphere circulation pattern at about half of surface pressure, 500mb.
There are two main differences between this year’s El Niño and 1998. This year more heat is in the central Pacific and less on the west coast than 1998. The other big difference is the effects of the ocean heat in the Atlantic and Arctic. The combined effects are sending much of El Niño’s rain to Alaska, leaving most of California in drought. Warm wet air has been flowing into Alaska from the southeast leaving Anchorage snow free.
Jason Ahsenmacher, a National Weather Service meteorologist based in Anchorage, said Monday the outlook is good for Anchorage to at least tie the 1958 record of 36 consecutive days without at least one-tenth of an inch of snowfall -- the minimum the federal agency considers measurable -- if there’s no snowfall by Friday. This week's forecast is not calling for significant chances of snow until Sunday.
...I edited the ADN article here for brevity to keep within fair use...
“There’s been a very strong North American ridge, which has been blocking the North Pacific jet and sending a lot of energy into the Gulf of Alaska,” Ahsenmacher said. “That right there is not a typical El Niño weather pattern.”
The arrival of those weather systems in Southcentral Alaska generates what Ahsenmacher calls “southeast flow,” or low-altitude winds blowing into the area from the southeast, perpendicular to the Chugach Mountains. Those systems tend to lose their precipitation prior to crossing the mountains, leaving Anchorage dry, while Whittier and parts of the Kenai Peninsula see heavy snowfall.
“Consistently we’ve been getting systems moving into the Gulf giving us southeast flow, so that’s a very downscale type of system for us,” Ahsenmacher said. “So we’ll have no snow here in Anchorage, while there’s 2 feet in Turnagain Pass.”
A article published in Geophysics Research Letters in 2004, in effect, predicted what’s happening with this El Niño. Jacob Sewall and Lisa Sloan at the Univ. of California Santa Cruz used atmospheric models to analyze the effects of sea ice loss on west coast climate and found that winter sea ice loss causes a ridge in the atmospheric circulation on the west coast.
These scientists were very cautious about their discovery which has been successfully built on by other studies. The technical description below, that I have already described using less technical language, fits the atmospheric circulation pattern that is taking place right now.
While we are confident in the causal relationship between reduced precipitation, changing stormtracks and increased 500 mb geopotential height off the west coast of North America, the association between these responses and changing Arctic ice cover is not as clear.
Our results suggest that the changes in, and offshore of, western North America are linked to changes in winter ice cover of the Greenland, Norwegian, Barents, and Kara Seas (not shown). Ice cover in this region is reduced by up to 50% in FARC and the increased open water results in a substantial change in outgoing energy (up to 80 W/m2; not shown). This increase in energy passed from the ocean to the atmosphere results in a substantial positive anomaly in 850 mb temperatures (up to 4C) over the Greenland, Norwegian, Barents and Kara Seas (Figure 3a). Increased 850 mb temperatures in FARC drive a large, positive 500 mb geopotential height anomaly in this same location (Figure 3b).
We hypothesize that this 500 mb geopotential height increase south of the Barents and Kara Seas perturbs the planetary wave pattern and contributes to the increased 500 mb geopotential heights offshore of western North America and, thus, decreased precipitation in this same region. (bold added)
Loss of winter Arctic sea ice heats the Arctic atmosphere forcing a flow of cool Canadian air into the eastern U.S. and building a warm dry ridge over the western United States.
The rapidly increasing heat content of the north Atlantic is bringing on two possible states:
1). A weak “Gulf Stream” that spares sea ice but supports intense hurricanes and storms and very cold weather in Europe.
2). A strong “Gulf Stream” that spares Europe the cold and has fewer intense hurricanes, but brings cold stormy winters to the east coast and drought to California and the western states.
In both states sea level rise can be expected to accelerate because Antarctic glacial melting is accelerating. The situation around Antarctica is as dire as the Arctic for a different set of reasons that I will discuss later. The build up of heat in the oceans is changing weather and ocean circulation patterns globally. Expanding and intensifying droughts in the western states are one consequence.