Environment Canada is predicting a colder than usual winter for most of the country this year.
Whatever happened to global warming?
Daniel Bezte, a teacher by trade who has a degree in geography specializing in climatology, says it is possible to have colder winters in parts of the globe and still have global warming.
Bezte, who spoke at an Outstanding Young Farmers national conference in Brandon in November, said a phenomenon called the Arctic dipole, which has developed over the Arctic the last several years, might be responsible for recent cold winters in parts of North America.
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Normally in the Arctic, there is low pressure in the upper atmosphere and high pressure closer to the Earth because cold air sinks, Bezte said.
“(But) that pattern has been breaking down periodically over the winter. We’ve seen those areas of low pressure move further south,” he said.
“One off the west coast and one toward the east coast of North America.”
High pressure is developing over the Arctic as part of the dipole phenomenon, which Bezte said “opens up the door in the Arctic” allowing cold air to flow south.
“Especially in the east coast (of North America),” he said.
“Everybody’s going ‘global warming? But look at all this cold and snow.’ Part of that is this strange weather pattern called the Arctic dipole.”
While Arctic dipoles have developed for months at a time during the last decade, meteorologist Jeff Masters said the air pattern alters summer temperatures rather than winter.
“The most important impact it has is on summer weather because it allows a lot of warm, southerly airflow into the Arctic … which enables much more ice melting to occur than would normally occur,” said Masters, director of meteorology for the Weather Underground, a weather service in Ann Arbor, Michigan.
Masters said a weather pattern called the Arctic oscillation has a more significant influence on winter weather in North America.
On its website, NASA describes Arctic oscillation as the difference between air pressure at 45 degrees north, which is approximately Montreal, and air pressure over the Arctic.
A low pressure mass normally sits over the Arctic and high pressure sits at the mid-latitudes. In that circumstance, cold air is confined to the
North Pole. If that pattern weakens and the pressure difference between the two latitudes decreases, air will seep out of the Arctic, causing cold winters in eastern North America and Western Europe.
Arctic oscillation certainly affects winter weather in North America, said David Phillips, senior climatologist with Environment Canada, especially temperatures in Eastern Canada.
Phillips said climatologists don’t really understand how Arctic oscillation interacts with more familiar weather patterns such as El Nino or La Nina.
“There is some linkage between the two (El Nino or La Nina and the Arctic oscillation), but what that is, is not well known,” said Phillips. “But as far as the West, it is principally the La Nina situation which allows the Arctic air to come unrestricted across the heart of North America.”
For example, a La Nina, defined as colder than usual water temperatures in the Pacific Ocean near the equator, should bring icy temperatures to Western Canada this winter.
“The flavour and personality of the winter, really from Vancouver Island right across the country, is looking like it is going to be colder than normal.”
