Pacific Northwest Heat Waves Impossible Without Human-Caused Climate Change

The recent heatwaves in Canada and the Pacific Northwest caused many seasoned climate watchers—including normally cautious climatologists—to essentially freak out. And with good reason. When heat records normally fall, they fall by fractions of degrees, with each new high just slightly inching out the high that came before it. What made the recent extreme heat so terrifying was that records were being smashed by as much as 8.3 degrees (4.6 degrees Celsius). 

In past years, scientists have been careful about attributing any one extreme weather event to human-induced climate change. As the frequency of such events increases, however, and as the evidence continues to mount that the climate crisis is largely responsible, a growing number of experts are looking for ways to responsibly communicate those connections. 

World Weather Attribution is a scientist-led effort that is working on this problem. Since 2015, it has been conducting real-time attribution analysis of extreme weather events as they happen. These studies—which are released before they are peer-reviewed for reasons of timeliness—provide the public, scientists, journalists, and decision-makers with a better understanding of how greenhouse gas emissions may be linked to extreme weather events, such as storms, floods, heatwaves, and droughts that they are currently living through.

Its latest effort, focused on the most recent heat wave, makes for some sober reading. Here are some of the biggest takeaways from the study:

• Based on observations and modeling, a heatwave with such extreme temperatures would have virtually impossible without human-caused climate change.
• In the most realistic statistical analysis, the event is estimated to be about a one in the 1,000-year event in our best understanding of today’s climate.
• If human-induced climate change had not raised temperatures as much as it already had, then the event would have been 150 times than even the 1 in 1,000 number. 
• Also, this heatwave was about 3.6 degrees (2 degrees Celcius) hotter than it would have been if it had occurred at the beginning of the industrial revolution.
• If the world continues to warm to an average of 3.6 degrees (2 degrees Celcius) of global warming above pre-industrial temperatures (which could happen as early as the 2040s), then an event like this would occur roughly every 5 to 10 years.

It’s all pretty scary stuff, but there is an even more disturbing detail included in the analysis. And that’s the fact that all of the statistics and probabilities outlined above are based on a fairly significant assumption—namely that the climate models we currently have are, broadly speaking, correct. 

There is also, however, another and even more worrisome possibility, which is spelled out on the World Weather Attribution website: 

“There are two possible sources of this extreme jump in peak temperatures. The first is that this is a very low probability event, even in the current climate which already includes about 1.2°C of global warming — the statistical equivalent of really bad luck, albeit aggravated by climate change. The second option is that nonlinear interactions in the climate have substantially increased the probability of such extreme heat, much beyond the gradual increase in heat extremes that has been observed up to now. We need to investigate the second possibility further...”

In other words, based on current models, the heatwave is highly statistically unlikely and would have been impossible without the warming we have already witnessed. It’s possible, however, that it is no longer all that unlikely—and that we are entering an entirely new climate where such extreme weather events are already likely to be fairly commonplace. 

Both possibilities are extremely troubling, but the second is significantly more troubling than the first. Having said that, however, the basic conclusions of what we have to do—in either case—remain largely unchanged. 

We have to cut carbon as fast as we possibly can. We have to build resilience within our communities to protect the most vulnerable from the extreme weather that we know is coming. And we have to restore and rejuvenate the natural systems on which we all rely so that the animals and plants around us can also weather the storms and challenges that are no doubt coming our way. 

Let’s get to work.