Monique Keiran: Jet-stream traffic jams to blame for weird weather

‘It would be more bearable if it weren’t hot,” Nature Boy said, waving his hand out the window at the scorched sky and blazing sun. “In this heat, every minute spent sitting here in traffic feels 10 times as long.”

We were on McKenzie Avenue at rush hour — poor planning on our part, made worse with it being one of the summer’s few hot, still and sticky days. The gamut of inching along, stopping, then starting again as the traffic lights allow tested the patience and forbearance of thousands of commuters heading toward the Trans-Canada Highway and away from Victoria.

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“The traffic’s bad, but at least the heat hasn’t been parked over us for weeks and weeks like it was last year,” he said.

Funny that he should say that. According to a study by American researchers, the formation of persistent heat waves, like the one eastern Canada experienced this summer, or long cold snaps, like the one we saw in February and March, is the result of atmospheric traffic congestion.

Many of our weather patterns are influenced by a vast river of super-fast wind called the polar jet stream that circles the planet at about 9,000 metres overhead, at speeds above 280 kilometres per hour. The jet stream is the tailwind that speeds eastbound jet aircraft to their destinations and adds minutes and even hours onto westbound flights.

It marks the boundary between the mass of cold Arctic air that covers the top of our planet and the warmer air around the middle.

The jet stream flows generally from east to west. However, it meanders off the straight-and-narrow path along the way. The twists and turns towards the north and south affects the pressure systems and wind patterns at lower latitudes throughout Europe and North America.

When the jet stream flows south, for example, it pulls masses of Arctic weather down to regions used to balmier temperatures. When it loops around and pushes its way back north, it hauls warmer temperatures from the south with it.

That north-south meandering can also block the prevailing winds that keep weather systems moving from west to east – effectively causing a traffic jam in the atmosphere.

Blocking is the atmospheric equivalent of shutting down the traffic lights along McKenzie and directing tens of thousands of additional vehicles to try to merge into or across the steady stream on McKenzie. Like highways, the jet stream has only so much capacity, researchers say, and when it’s exceeded, atmospheric traffic comes to a standstill.

As a result, weather systems can become parked over a region for long periods.

Other scientists have shown that the jet stream’s meandering has become more frequent in recent decades. The researchers sampled cores from 300-year-old trees across Europe. The cores record in the trees’ growth rings what kind of weather the continent experienced each year. Those rings showed that, since 1960, the number of years when the jet stream has shifted to the extreme north or south has increased significantly and without precedent in the trees’ history.

Many researchers think climate change is causing the increased rate and extent of meandering. The difference in temperature between Arctic regions and southern regions powers the jet stream. Because hot always runs to cold, the jet chases the cold, lower-pressure northern systems, moving heat from the tropics toward the poles and forcing cold air toward the tropics.

The greater the temperature differences between those two regions, the straighter the jet stream’s path.

However, scientists have documented in recent years that the Arctic is warming almost twice as fast as other regions, and the north-south contrast in temperatures is decreasing. This is causing the jet stream to weaken and to divert north and south to more extreme extents.

Remember Victoria this past winter, when snow fell early in February and stayed into March? Recall those frigid temperatures and blizzards in Ontario and the eastern U.S.? That was work of a wandering, congested jet stream.

This summer’s heat wave in eastern Canada and Europe? More blockages in a wavy jet stream.

Slow rush-hour traffic on McKenzie? Blame ongoing construction and the number of vehicles trying to head west on the Trans-Canada Highway.

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