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Global warming, melting arctic ice and extreme weather

Attributing global warming to extreme weather events

Ten years ago, from a climate science perspective, trying to attribute the production of a particular Category 3 hurricane in the North Atlantic to global warming (such as Hurricane Sandy that hit New York City in 2012) would have been considered risky.

Today it is well known that for the past century the earth’s seas have been absorbing solar energy that has not returned to the atmosphere. As a result, the average temperature of the seas is increasing. Climate scientists are now investigating how global warming is affecting what would be considered extreme weather events in certain geographic areas. Swanson (2013) summarizes the idea of ​​the relationship between the greenhouse effect, global warming and extreme weather events, noting that the probability of these extreme weather events is increasingly related to man-made global warming: too much is emitted carbon dioxide in the environment This is no longer an abstract idea. It is felt on all levels. [1]

Global warming and the melting of the Arctic ice

As a result of global warming, temperatures in the Arctic Ocean have been increasing. This higher temperature is extending the melting of the Arctic ice in the summer well into the fall and winter. Arctic areas that were previously covered in reflective white snow have now been replaced by dark areas of land and sea that do not reflect sunlight. Estimating the amount of glacial mass lost in Greenland, Jay Zwall of NASA’s Goddard Space Flight Center noted that “20 percent more” ice comes out of the snowfall each year. Bielo (2006) [2] Since this sunlight is no longer reflected, this energy is now absorbed by the ocean, causing further warming of the sea and reinforcing the melting effect of the Arctic ice shelf.

This melt is causing significant changes in the Jet Stream (narrow, fast-moving westerly winds that flow west to east over the northern parts of the US, Canada, Europe, and Asia), which is the gradient pressure (difference) in the atmosphere. affecting the winter weather of the northern midlatitudes.

Fundamental changes in the Jet Stream are caused by Global Warming

The jet stream can be seen as waves in crests and troughs moving around the center of the northern hemisphere and gently bending north and south. The temperature gradient (difference) between the latitudes of the Arctic and the latitude of the North Atlantic is reduced in autumn, when the Arctic Ocean releases the additional solar energy absorbed by the incremental melting of the ice produced by global warming. So, the difference in air pressure between the two pressure fields is also reduced, and the speed of the jet stream’s west to east winds is also reduced.

Two pressure fields are present in the northern hemisphere. The Arctic Oscillation, or AO, -field of positive or negative pressure- that covers from parallel 70° north latitude to the North Pole, and the North Atlantic Oscillation, or NAO, -field of positive or negative pressure- that covers from parallel 70° north latitude to the subtropics. Now, since the NAO pressure field affected by global warming is more likely to be negative in autumn and winter, the Jet Stream is more likely to be disturbed in winter.

Extremely hot winters in the US and cold in Europe 2011-2012

As mentioned above, global warming has an effect on the extent of melting of the Arctic ice. The sea absorbs most of the sun’s energy in the summer, and then this heat is released by the Arctic Sea in the fall, reducing the pressure gradient (difference) between the Arctic Oscillation pressure field and the pressure field of the North Atlantic Oscillation, and the Jet Stream slows down. The pressure gradient between the AO and the NAO becomes brittle, making it easier for a larger Jet Stream curve to extend further north or south.

Winter 2011-2012

During the winter of 2011-2012, extremely warm temperatures developed in the Northeastern United States. The jet stream tipped further north than usual over the US northeastern mid-states, allowing warm semi-tropical air to drift as far north as the US-Canada border and stay there for a long time. In addition, La Niña (which means the pressure oscillation that originates in the South Pacific) was also present. This weather phenomenon tends to deflect the jet stream northward over the northeastern US.

Simultaneously, in Eastern Europe, the coldest winter in 25 years occurred in 2011-2012. The pressure gradient (difference) between the NA and the NAO was weak due to the additional heat released by the sea in autumn from melting of the Arctic ice caused by global warming. The Jet Stream spread further south, causing air from the Arctic to reach locations in Eastern Europe and stay there longer than usual, producing major frostbite. Fischetti (2012) summarizes all of this, stating that as more Arctic ice melts in summer, this will result in longer jet stream curves and longer stays in place, making winters warmer or colder. usual. [3]

there are no normal winters anymore

Scientists are investigating how the Arctic ice pack has been melting as a result of global warming. The question now is: Why is the Arctic ice melting faster than computer models can predict from global warming?

As global warming continues, it is likely that the melting process of the Arctic ice and its effect on Northern Hemisphere pressure fields will continue to push the jet stream pattern further north or south in large curves. Normal, regular winters will no longer be the norm.

By Alfonso de Garay

May 2014

References:

[1] Swanson, Jeanene. 2013. “Cloudy, Typhoons Chance,” Storm Warnings: Climate Change and Extreme Weather, Publishers of Scientific American, 12/11/13 eBook

[2] Biello, David. 2006. “Greenland’s glaciers are leaving, they are leaving…”

Scientific American online, October 19, 2006

[3] Fischetti, Marcos. 2012. “The Northern Hemisphere could experience extreme winters”,

Scientific American online, October 30, 2012

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