The Canadian heatwave is obviously extreme weather, not climate, and we all know that weather can break records – it happens all the time.

High-pressure circulation in the atmosphere acts like a dome or cap, trapping heat at the surface and favoring the formation of a heat wave. Source: NOAA

Canada and parts of United States are experiencing very hot summer temperatures. This particular heatwave is mainly driven by a ‘heat dome,’ as NOAA explains:

Summertime means hot weather — sometimes dangerously hot — and extreme heat waves have become more frequent in recent decades. Sometimes, the scorching heat is ensnared in what is called a heat dome. This happens when strong, high-pressure atmospheric conditions combine with influences from La Niña, creating vast areas of sweltering heat that gets trapped under the high-pressure “dome.”

A team of scientists funded by the NOAA MAPP Program investigated what triggers heat domes and found the main cause was a strong change (or gradient) in ocean temperatures from west to east in the tropical Pacific Ocean during the preceding winter.”

The Guardian says nowhere on Earth is safe according to climate scientists. That is their conclusion as they see the intense record-breaking heatwave in western US and Canada over the past week. Actually, it’s just Sir David King, the former UK chief scientific adviser who says that, “Nowhere is safe … who would have predicted a temperature of 48/49C in British Columbia?”

Who indeed? So let’s look in more detail at what has happened.

The hand of climate change is not readily apparent in the basic cause of the heatwave. It’s a result of extremely rare meteorological conditions with hot desert air positioned over the Cascades. The temperature has also been increased because of air sinking after having passed over mountainous regions – the Fohn effect. It’s obviously weather, not climate, and we all know that weather can break records, it happens all the time.

Looking at weather-station data from the region shows no upward trend over the past century in any of the parameters measured. You can also look at duration of heatwaves, in particular the number of days 100F and over. These peaked in the 1990s, since when heatwave days have returned to what it was previously.

But has climate change somehow boosting an unusual weather event? It clearly didn’t start from an unusual condition that was already ramped up in temperature or some other parameter. So what could be going on?

We don’t know but we really do know is the confusing answer from many scientists. Nobody is sure what exactly is going on but many are sure what is going on even after they have expressed some uncertainty! Roger Harrabin of the BBC says “We can’t say for certain…” and speaking to LBC Professor Joanna Haig said it was “very, very likely” that it’s down to climate change,” then adding another layer of positive opinion by saying,” It’s pretty certainly exaggerated by climate change.”

It is all to be expected. During this recent heatwave Michael Mann has reiterated the prediction that as the planet warmed up such dangerous weather events would become more common, “You warm up the planet, you’re going to see an increased incidence of heat extremes.”

But it’s worse than that. Even though climate science has predicted what many say is coming to pass, that very climate science is inadequate according to Mann because it fails to capture the scale and seriousness of what was happening. It’s apparent that for some science is an ally when it comes to general supportive statements that one agrees with, but then science is abandoned when it cannot provide the evidence needed to go further and convince others one is right. In such important issues you have to go beyond science and be guided by what you think is happening, having the insight to know that science will catch up!

Extreme events are part of the pattern to be expected. Haig said, “it all fits in” adding that it’s exactly the sort of extreme events scientists have warned of, “it’s pretty certainly exaggerated by climate change,” she adds.
It must be true. Such a heat dome event is according to the UK Met Office “almost impossible” without climate change being an event to be expected once every tens of thousands of years. Michael Mann in the New York Times says it’s a “once in a millennium event,” but not under the effects of climate change, we are rolling loaded climate dice he adds. Might the heatwave has been as bad without climate change he asks himself. His answer, “almost surely not.”

So let’s pause and asses the state of the rhetoric if not the science pertaining to the heatwave. Let’s just repeat a few phrases we have come across:

‘Extreme meteorological event… No long term trend in temperature… Once in tens of thousands of years… Pretty certainly… Once in a millennium… Very, very, likely… It all fits in… We can’t say for certain.’


Drawing together this admixture the Guardian quotes Sir David King who says ‘nowhere is safe’ (presumably not even Antartica) from the kind of extreme heat events that have hit the western US and Canada in recent days. He urges governments to dramatically ramp up their efforts to tackle the escalating climate emergency. If you want evidence of a climate emergency, look at the Canadian heatwave over the past week without putting it into any kind of historical perspective.

‘Whilst we cannot be certain about the role of climate change in the recent heatwave the risk is growing,’ say some. Peter Stott of the UK Met Office says, “The risk of heatwaves is increasing across the globe sufficiently rapidly that it is now bringing unprecedented weather and conditions to people and societies that have not seen it before…Climate change is taking weather out of the envelope that societies have long experienced.”

Despite the historical record showing that heatwaves were just as bad in the past Stott might be right. He might be wrong. “We can’t say for certain.”


Feedback: David.Whitehouse@thegwpf,com

The post A Canadian heatwave & the heat dome: unprecedented or unusual? appeared first on The Global Warming Policy Forum.

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July 2, 2021