The blizzard of January 2016, a crippling storm that buried the U.S. East Coast in snow, could be tied to a weakening ocean current that transfers heat from the tropics to northern climes, according to one leading scientist.
Stefan Rahmstorf, an oceanographer at Potsdam University, thinks that a slowing Gulf Stream may have contributed to excessively warm ocean temperatures along the East Coast. He discussed his theory on the blog RealClimate.
The Atlantic Ocean is presently 3 degrees Fahrenheit warmer than normal, and the air above it has about 15 percent more moisture. This moisture-rich air flowed into the blizzard and likely increased snowfall amounts (ClimateWire, Jan. 25).
The resulting snowstorm covered 434,000 square miles and affected 102.8 million people, according to the National Oceanic and Atmospheric Administration. Some 24 million people got more than 20 inches of snow. NOAA rated the storm Category 4, or “crippling,” on a 5-point scale ranging from “notable” to “extreme.”
“This storm ranks up there with the great blizzards of the past 100 years in terms of amount of snowfall, size of impacted areas and population affected,” said Paul Kocin, a meteorologist at NOAA’s National Weather Service, in a statement.
This storm’s rapid evolution could be traced to events in the Atlantic Ocean, Rahmstorf suggests. There, the Gulf Stream, also known as the Atlantic meridional overturning circulation, or AMOC, acts as an ocean conveyor belt that transfers heat, nutrients and water from the tropics to the North Atlantic. It is responsible for the relatively mild temperatures year round in European nations that are roughly on the same latitude as frigid Canada.
The Gulf Stream is such a massive heat carrier that scientists watch it keenly for signals of its demise. Studies have shown that the Gulf Stream does slow and speed up periodically. It slowed between the 1930s and 1995, and then seemingly recovered.
A complete stop would affect the livelihood of people in northern and western Europe. Climate models project a slowdown of AMOC by 2100 if nations continue emitting greenhouse gases at present-day rates.
A strange, cold spot
In the North Atlantic, almost at the tip of Greenland, the salty, dense waters of the AMOC cool and sink into the depths, releasing heat to the atmosphere. The region is called the subpolar gyre.
In recent years, scientists have noticed that the North Atlantic has developed an anomalous cold spot in this region. In 2014 and 2015, almost all ocean basins were record warm except for the subpolar gyre region, which was record cold, according to NOAA. That is unusual, since it should have been warmed by the AMOC’s tropical flow.
The blob may indicate that the AMOC has slowed, said Tom Karl, director of NOAA’s National Centers for Environmental Information, last week.
“That’s something that we have looked at in the science community—there is lots of interest because it has potential implications on regional weather patterns,” he said.
An ocean-monitoring array in the Atlantic, called RAPID, has found that the AMOC has indeed been weakening since 2004. But the open question is whether this slowdown will be a persistent long-term trend linked to climate change. A decade of data is not enough to detect long-term trends.
The observed AMOC slowdown could well be due to internal variability, said Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, in a press call last week.
“We don’t anticipate it [a slowdown] quite yet,” Schmidt said.
What could have caused the blob?
Rahmstorf thinks otherwise, that the slowdown is persistent and linked to global warming. Climate models simulating the AMOC slowdown out to 2100 have predicted this cold blob in the North Atlantic and a simultaneous ocean warming on the U.S. East Coast, according to Rahmstorf.
These anomalies are the fingerprints of an AMOC slowdown, a fingerprint that has been seen in the Atlantic in recent years, he wrote.
Other climate models have tied the warmer ocean to cold weather anomalies on the East Coast, he wrote.
“I think this connection is worthy of further investigation,” he wrote.
In a study last year, Rahmstorf found that Greenland ice melt, linked to global warming, contributed to AMOC slowdowns in the 20th century. The fresh water flowing off ice sheets diluted the AMOC and made it difficult for waters to sink near Greenland.
Schmidt is more cautious. He said that although Greenland has lost ice mass since the 1900s, the volume is insufficient to slow down the AMOC.
“It is not really enough, given our understanding, to have a major effect on the overturning circulation as yet,” he said.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500