Why global warming gg does not necessarily result in warmer winters

From:	Victor Okpanachi

ON FEBRUARY 26th James Inhofe, a senator from Oklahoma, threw a snowball at another senator inside America's upper chamber. He did it to back up his contention that man-made climate change is not the threat President Barack Obama (and many others) say it is. Mr Inhofe is chairman of the Senate's environment committee and his argument has a simple and persuasive logic: much of the United States has experienced four unusually freezing winters in succession. Surely that contradicts the notion that the Earth's climate is warming up?





Not necessarily, for two reasons. First, the climate and the weather are not the same: they are related, but weather patterns develop and change over hours, days and weeks; the climate changes over years and decades. And second, the American landmass is just one small part of the surface of the globe. While temperatures have been well below average across much of the United States, other parts of the world have been abnormally warm. And indeed, there may be a connection between climate change and colder winters in parts of the northern hemisphere. The link is the Arctic region. Because the poles are colder than the equator, air streams north and south in order to equalise temperatures. In the northern hemisphere, this flow is called the jet stream. Because of the rotation of the Earth, the stream turns right as the planet spins, and flows in a wavy line around the pole, like a badly cut monk's tonsure. In the northern hemisphere the jet stream brings up warmer air from the south, producing more temperate weather in the northern regions over which it flows.

But the Arctic is warming faster than the rest of the Earth. Since the mid 1990s, temperatures at the northern pole have risen almost three times as much as they have at temperate latitudes. So the difference between the poles and the equator is narrowing. This seems to be affecting the jet stream, and could change its moderating effect on northern weather. According to Jennifer Francis of Rutgers University, in the northern hemisphere westerly wind speeds seem to have weakened since the mid 1990s. As the flow has faltered, the undulations of the jet stream have become more marked, with gentle waves turning into bigger loops. Inside the loops, low-pressure areas of cold air build up, producing "polar vortices" and other freezing weather patterns in America and (especially) northern Siberia—even while the Arctic warms.

Dr Francis's explanation is controversial. An article in Nature Geoscience in October 2014 supported her ideas, saying the retreat of the Arctic sea ice had roughly doubled the probability of severe winters in Europe and Asia. Other researchers, such as Elizabeth Barnes of Colorado State University, have raised doubts about the statistical links between changes in the Arctic and the jet stream. The scientific controversy is likely to rumble on—and while it does, senators can continue to throw snowballs.