Polar vortex and climate change

It’s been super cold. Even Donald Trump is feeling it down in Palm Beach

On 28 December 2017 at around 6pm, the city of Ottawa, the capital of Canada, clocked in at a temperature of – 29C. On that particular day Ottawa was colder than the North Pole.

At the same time, the town of Erie in Pennsylvania, USA, was digging itself out from under a metre and a half of snow, and Toronto was under a severe weather warning as tempertures dipped below -17C during the day—about 16C below normal.

So do these frigid temperatures and huge snowfalls signal the end of global warming?  Is it all a hoax after all?

It’s a reminder that climate and weather are two different but related phenomena.  Climate describes the underlying trend. Its subtle changes are measured in small incremental amounts—fractions of a degree of temperature increase; milliimetres of sea level rise; the small percentage reduction in Arctic sea ice extent. Weather, on the other hand, is all about the action that plays out on the climate stage.

A warming climate brings with it extreme weather—hurricanes, cyclones, droughts, floods and wildfires. The world in 2017 has experienced all these extreme events and more.  But paradoxically, the warming climate can also bring bone-chilling cold weather to northern latitudes during the boreal winter months.

The period of frigid temperatures that froze eastern Canada and the UK at the end of December 2017 has been called a ‘polar vortex’.  This phenomenon occurs when the jet stream that sweeps around the North Pole, and which usually acts as a barrier keeping frigid polar air close to the Pole, weakens and starts to meander around, allowing extremely cold air to descend much farther south—as far as southern Ontario in Canada, the northeast US, the United Kingdom, and across northern Russia.

The reason why this phenomenom occurs, and why it now seems to happen more often, is the subject of intense scientific scrutiny.  Readers can find lots of interesting information and scientific analysis by checking out the NASA and NOAA websites.

As for the huge amounts of snow dumped on the town of Erie, here we have an explanation firmly grounded in climate change.

Warmer temperatures are increasing the intensity of lake-effect snow.  If the Great Lakes aren’t frozen, cold winter winter air sweeping across the water becomes warmer and more humid. It then rises, the water vapour freezes, and gets dumped as snow. The data support this explanation.  For 15 of the last 20 years, ice cover on the lakes has been below the long-term average. And when the lakes do freeze, it is often for a shorter period of time—once again increasing the chance of lake-effect snowfall.

President Trump also seems to be feeling the cold.  On December 28, while down in Mar-a -Largo where temperature were a few degrees below normal, he tweeted that “perhaps we could use a little bit of that good old Global Warming’.  This is his way of disparaging and minimising climate change—by treating it as if it’s a bit of a joke.  For Donald Trump, climate change is only about global warming and that’s just some hot weather—nothing more.

Personally, I’m pleased that Trump is taking an interest in the weather.  He should take a look at a report just published by the American Meteorological Society (AMS). Titled Explaining exteme events of 2016 from a climate perspective, the report presents three research papers that for the first time conclude that “the extreme magnitude of a particular weather event was not possible without the influence of human-caused climate change.”

The three events studied by the researchers are the 2016 global heat record; the record heat over Asia in 2016; and the persistence of an area of anomalously warm ocean water off the coast of Alaska—called ‘the blob’.

In each case the climate scientists conclude that these phenomena are beyond the bounds of natural variability. They can only be explained by human-caused climate change.

This is important because there are many studies thar present evidence that climate change has influenced and intensified a particular event.  In the AMS report, 21 of the 27 papers identified climate change as a significant driver of an event, while six did not. Those events were just weird weather and hey, that happens. But studies that conclude that an extreme weather event would not have taken place without climate change are new.

So whereas before climate change was just making things worse—exacerbating natural variability. Now it’s actually causing the extreme weather and creating weird phenomena we’ve never seen before.

So pay attention. It’s started.

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