Historic cold and global warming can co-exist: Here's how

Wednesday, February 18, 2015, 6:25 PM - How can the current historic cold snap possibly square with climate change and the long term trend of global warming?

Before I delve into an explanation, the brutal February cold snap needs to be prefaced by a few facts:

• Toronto Pearson is on pace for its coldest February on record since observations began in 1937
• This February looks to place in the top five coldest on record for the downtown Toronto weather station at the University of Toronto which has been recording temperatures for 175 years
• If you were born (and lived) in Toronto from 1934 on, the reality is you have lived your entire life without experiencing a colder February. That's 81 years.
  

So, back to the original question: How can this historic cold be mentioned in the same sentence as climate change and the long term trend of global warming?

First of all, climate and weather are two different things. Climate is how our atmosphere looks over years, decades, centuries and millennia – both the averages and the extremes. Weather is what the atmosphere is doing at any given point in time. We experience weather. We don’t experience climate.

At any given time, there are places in the world that are experiencing much warmer weather than normal, and places seeing much colder weather than normal.

It turns out that for the month of February so far, the coldest air relative to normal over the entire globe has been parked from Ontario through Greenland. On the flip side, the highest temperatures relative to normal have been across the western U.S. extending into southern British Columbia. North America is a continent divided.

CAPTION: Global temperature departures from normal for February so far. Orange/red shading is above normal, blue/green/purple shading is below normal. Courtesy: WeatherBell.

Averaging out all of the hot and cold spots so far in February, global temperatures are still above normal as compared to the 30 year average from 1981-2010. So the bottom line is that a cold snap or warm spell at a given time in a given part of the world means nothing in the context of climate change. The big picture must be considered – in both space and time.

Another fascinating way to measure the current cold snap across southern Ontario is to look at how this cold snap compares with the coldest in history. Taking the 7-day period beginning on Valentine’s Day and ending this Friday (the 20th), Toronto is in the midst of the fifth-most severe cold snap in 100 years.

That’s a WOW stat. It rarely gets much colder than what some Canadians are experiencing now.

Meteorologist Patrick Cool, our resident statistician, crunched the numbers going back 175 years to measure the severity of the coldest 7-day stretch for each winter. What he found was that, despite the current brutal cold snap, the severity of cold snaps in Toronto has generally been lessening.

CAPTION: Severity of cold snaps (as measured by the coldest 7-day average temperature in a winter) for Toronto since 1840. Note the severity of this current cold snap (last data point on the right where the blue line goes way down). Also note the overall trend line showing lessening severity over the period.

This is by no means a rigorous scientific analysis – but it’s a great visualization to indicate both the severity of the current cold snap, and the overall context of the trend towards less intense cold snaps.

The bottom line?

Yes, a brutal stretch of cold weather and global warming can co-exist. Climate and weather are two different things.

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