As the United States has a freakishly warm and calm winter, Europe has been experiencing a frighteningly cold and dangerous season. Hundreds have died in frigid temperatures, snow and ice storms, and floods. This freakish weather in the Northern Hemisphere is connected by unusual behavior in the jet stream, which scientists are attributing to the dramatic changes in the Arctic caused by global warming pollution. In a new paper published in Tellus, scientists at the Alfred Wegener Institute for Polar and Marine Research find that declines in summer Arctic sea ice are a factor in changing the Arctic Oscillation, the circulation pattern that dominates winter weather:
Scientists at the Alfred Wegener Institute for Polar and Marine Research in Potsdam, Germany, say the frigid, snowy European winter has its origins in a warm Arctic summer. The U.S. National Oceanic and Atmospheric Administration reported that July 2011 was the fourth-warmest July on record. A warm summer in the Arctic cuts the amount of sea ice. NOAA reports that sea-ice levels last July were the lowest in three decades.
The effect is twofold, the Wegener scientists report. First, less ice means less solar heat is reflected back into the atmosphere. Rather, it is absorbed into the darker ocean waters. Second, once that heat is in the ocean, the reduced ice cap allows the heat to more easily escape into the air just above the ocean’s surface. Because warmer air tends to rise, the moisture-laden air near the ocean’s surface rises, creating instability in the atmosphere and changing air-pressure patterns, the scientists say.
In an interview with Conducive Chronicle, Dr. Jeff Masters explained why greenhouse pollution should be considered the most likely suspect for unprecedented behavior in the climate system:
The laws of physics demand that the huge amount of heat-trapping gases humans are pumping into the atmosphere must be significantly altering the fundamental large-scale circulation pattern of the atmosphere. Unprecedented behavior like we’ve witnessed in the configuration of the winter jet stream over North America — with the four most extreme years since 1865 occurring since 2006 — could very well be due to human-caused climate change. Something is definitely up with the weather, and it is clear to me that over the past two years, the climate has shifted to a new state capable of delivering rare and unprecedented weather events. Human emissions of heat-trapping gases like carbon dioxide are the most likely cause of such a shift in the climate.
It’s critical to note that the southern hemisphere is also experiencing utterly extreme weather during its summer: Australia is deluged by flood, and heat waves and drought are crippling South America and Africa.
Weather Channel meteorologist Stu Ostro, a former skeptic of the science of climate change, writes that this winter’s weather — shattering historical records, destructive, and utterly extreme — is yet more evidence that climate scientists were right to warn that greenhouse pollution would fundamentally alter our climate system:
Weather extremes have existed for as long as there has been weather on Earth. That’s a fundamental reason why as a meteorologist who is routinely observing them I was so skeptical for so long that anything was out of the ordinary.
However, increasingly during the past decade or so, the extremes have been so frequent, and so extraordinary, and sometimes even at the same time and in such close geographical proximity to each other, that I have become convinced that something ain’t right. That while there have always been extremes, their nature is changing.
This winter convinces me even further.