New Research Linking Ice Loss, Snow Loss, and Extreme Weather
December 9, 2013
Above, Dr. Jennifer Francis of Rutgers, and Dr. Jeff Masters of Weather Underground and the Weather Channel, on jetstream changes that may be responsible for changes in extreme weather events in the temperate zones.
Dr. Francis has a new paper just out reinforcing the sea ice connection with information about declining spring snow cover as well.
The past decade has seen an exceptional number of unprecedented summer extreme weather events in northern mid-latitudes, along with record declines in both summer
Arctic sea ice and snow cover on high-latitude land. The underlying mechanisms that link the shrinking cryosphere with summer extreme weather, however, remain unclear.
Here, we combine satellite observations of early summer snow cover and summer sea-ice extent with atmospheric reanalysis data to demonstrate associations between summer weather patterns in mid-latitudes and losses of snow and sea ice. Results suggest that the atmospheric circulation responds differently to changes in the ice and snow extents, with a stronger response to sea-ice loss, even though its reduction is half as large as that for the snow cover. Atmospheric changes associated with the combined snow/ice reductions reveal 0 widespread upper-level height increases, weaker upper-level zonal winds at high latitudes, a more amplified upper-level pattern, and a general northward shift in the jet stream.
More frequent extreme summer heat events over mid-latitude continents are linked with reduced sea ice and snow through these circulation changes.
Andrew Freedman has more.
A new study for the first time found links between the rapid loss of snow and sea ice cover in the Arctic and a recent spate of exceptional extreme heat events in North America, Europe, and Asia. The study adds to the evidence showing that the free-fall in summer sea ice extent and even sharper decline in spring snow cover in the Northern Hemisphere is reverberating throughout the atmosphere, making extreme events more likely to occur.
There is virtually no controversy among climate scientists and meteorologists that massive changes have occurred in the Arctic environment during the past three decades, and that those changes are largely due to manmade greenhouse gas emissions.
Since the 1980s, Arctic sea ice extent has dropped at a rate of about 8 percent per decade during September, which is when the sea ice cover reaches its annual minimum. Arecord minimum was set in 2012. For a size comparison, consider that the area of summer sea ice lost since the 1980s would cover about 40 percent of the continental U.S., the study said.
Spring snow cover extent loss during June has dropped even more precipitously than sea ice cover, the study found, at a rate of about 18 percent per decade since 1979.
The case for a connection between Arctic warming and summertime extreme weather events rests on the Arctic’s crucial role as a pacesetter and shapemaker of the jet stream, the powerful ribbon of upper level winds that steer weather systems from west to east across the Northern Hemisphere.
Because the temperature contrast between the frigid Arctic and the milder mid-latitudes is what drives the powerful jet stream winds that guide weather systems, what happens in the Arctic is bound to have some sort of influence on the world’s weather.
The new study, along with other previously published research, showed that the decline in sea ice and snow cover has slowed the west-to-easterly component of the jet stream, thereby enhancing the north-to-south waviness of the jet, which leads to the creation of more stagnant or “blocked” weather patterns. In addition, the new study found an association between sea ice and snow cover decline and a northward shift in the jet stream, which allows more warm air to move into the U.S. and Europe during the summer.
Paradoxically, other studies, including work by the same team of researchers, has shown that Arctic warming can actually enhance cold weather extremes in the U.S. and Europe during the winter.
Jennifer Francis, a meteorologist at Rutgers University, co-author of the new study, and the most prominent proponent of the hypothesis that Arctic warming is leading to more extreme weather events, told Climate Central that this study adds further evidence to the growing body of research supporting her team’s conclusions.
“While an observational study cannot pin down the mechanistic cause of the response, our results show a strong relationship between ice and snow losses during summer with heat waves in mid-latitude continents where billions of people are affected,” Francis said in an email conversation.
The cause/effect between arctic change and jetstream is not settled, pound on the table science. Below, an exchange between Dr. Francis and Dr. Kevin Trenberth, a leading researcher at the National Center for Atmospheric Research. Dr. Trenberth is not yet ready to sign on with the theory, but agrees that extreme weather events are increasing, and that we are seeing a “new normal” in climate.
Judah Cohen, lead seasonal weather forecaster at AER, a weather and climate consulting firm, said the possibility that Arctic climate change is leading to more extreme weather patterns has initiated a flurry of new studies. “I can tell you that I am busier now reviewing journal papers than I have ever been in my career and they are all on sea ice” he said in an email. “I think this will be a dominant area of research and discourse for years to come.”
For her part, Francis is continuing to keep a wary eye on the weather map, convinced that the evidence for Arctic-induced weather extremes will continue to mount.
“As we continue to emit ever-increasing amounts of greenhouse gases into the atmosphere and as the Arctic continues to warm faster than mid-latitudes, we will see the case for the linkage strengthen,” Francis said. “I expect that with every year we will see a clearer response of weather patterns in all four seasons, and new modeling experiments will help elucidate the links in the chain, as well.”
I am at the American Geophysical Union meeting this week, and will be seeing and interview Dr. Francis, Dr. Masters and Dr. Trenberth, among others. Will have more updates and videos in coming weeks.