Thread by @sambartusek

☀️My first PhD paper is out today! We investigated the extraordinary 2021 PNW heatwave🔥(+ Kai Kornhuber @KKornhuber & Mingfang Ting @mfting), identifying processes that supercharged it and their relations to climate change. @NatureClimate Link: nature.com/articles/s4155…

Here’s a free access link to the pdf: rdcu.be/c0lXW

We found that atmospheric dynamics played a key role in the PNW #heatwave: leading up to it, the jet stream bent into a huge hemisphere-wide wave—forming a heat dome in the PNW that was likely boosted by a smaller atmospheric wave coming off the Pacific.

We also found that in some areas of the PNW, dry soils likely strengthened the heating (especially where temperatures became most severe). Meanwhile, a model experiment showed that land–atmosphere interactions may make extremely hot summer months in the region much more common.

At the peak of the PNW #heatwave, conditions departed sharply from historical linear relationships between climate variables—which may suggest that these physical relationships between variables become modified under very extreme conditions.

These nonlinear interactions were likely catalyzed by climate-change-driven trends. This raises a more speculative question of whether the most extreme heat may increase faster than the mean. (See agupubs.onlinelibrary.wiley.com/doi/abs/10.102… @IslaSimpson4 for some evidence in model projections)

Relatedly, we did find some evidence that land–atmosphere coupling may have strengthened over recent decades in some areas of the PNW, especially those that experienced extreme heat during this heatwave.

Bottom line: #globalwarming to date severely increased the PNW #heatwave’s likelihood—turning it from virtually impossible to a ~once-in-hundreds-of-years event at current warming. Further emissions will make a similar event even more likely, possibly occurring decadally at 2°C.

In our view, the 2021 PNW #heatwave may be thought of as driven by *extreme* anomalies in *common* heat drivers, similarly to those described in nature.com/articles/s4155… @erichfischer (suggesting that such record-shattering events are essentially future events come early).

We therefore see the 2021 PNW heatwave less as a “black swan” (essentially unpredictable) than as a “gray swan” (more plausible, somewhat foreseeable) due to #climatechange—and suggest that its drivers may also have been altered by ongoing climate trends.

The 2021 PNW #heatwave, due to its shocking unprecedentedness, can shed light on the mechanisms of the *most extreme* extremes. See our Research Briefing here: nature.com/articles/s4155… @KKornhuber

See coverage of our paper and one very recently from @MichaelFWehner et al. here:

https://twitter.com/latimes/status/1595855019974197249