The harsh winter in Europe caused a rare event of Venice freezing over.
As global temperatures have risen, the area of Arctic Ocean covered by ice in summer and autumn has been falling.
Writing in Proceedings of the National Academy of Sciences (PNAS), a US/China-based team show this affects the jet stream and brings cold, snowy weather. From 2007 to 2011, large parts of the U.S., northwestern Europe, and northern and central China experienced early or abnormally heavy snowfall. A climate model created by the U.S. National Center for Atmospheric Research pinpointed two mechanisms for how a decline in sea ice could lead to more snowfall.
The paper, published on February 27th, demonstrates a link between the decline of arctic ice and Winter weather. While still early in research, and this is not the only factor affecting winter weather, it is the only one showing a consistent downward trend. You can find the supplemental data for the paper here.
BBC News Describes how the link works:
If less of the ocean is ice-covered in autumn, it releases more heat, warming the atmosphere.
This reduces the air temperature difference between the Arctic and latitudes further south, over the Atlantic Ocean.
n turn, this reduces the strength of the northern jet stream, which usually brings milder, wetter weather to Europe from the west.
It is these “blocking” conditions that keep the UK and the other affected regions supplied with cold air.
The researchers also found that the extra evaporation from the Arctic Ocean makes the air more humid, with some of the additional water content falling out as snow.
According to David Rind, a climate scientist at NASA’s Goddard Institute for Space Studies in New York City told National Geographic:
The atmospheric dynamic is so variable, and the basic equations of motion on the time scale that we’re discussing have so much inherent variability in them that you can have the same situations next time but everything is different. This year also has very little Arctic sea ice, but it’s going to be one of the warmest winters on record in the United States. The snowfall totals have been abysmal. … And in Europe the cold air did not come in the beginning of winter, but later
The challenge is to determine how much of these anomalies are caused by global warming.
I think the only thing that will ultimately answer that is the durability of the effect. If, year after year, we’re getting the same type of effect, that then looks like it’s not a variability issue but a climate change issue.