Extreme Heat Risk Rising Rapidly for Pacific Northwest

May 6, 2023

Still possible to learn things on twitter, if you follow the right people.
Michael Wara points to a recent Nature paper showing rapidly increasing odds for heat events in the Pacific Northwest (PNW) rivaling the astonishing occurrence in June, 2021. (see video review above)
Such an event has no parallel in the last 1000 years, but could become a 1 in 2 year event by midcentury, with no action.

Nature – Unprecedented 21st century heat across the Pacific Northwest of North America – 17 Feb 2023:

Extreme summer temperatures are increasingly common across the Northern Hemisphere and inflict severe socioeconomic and biological consequences. In summer 2021, the Pacific Northwest region of North America (PNW) experienced a 2-week-long extreme heatwave, which contributed to record-breaking summer temperatures. Here, we use tree-ring records to show that summer temperatures in 2021, as well as the rate of summertime warming during the last several decades, are unprecedented within the context of the last millennium for the PNW. In the absence of committed efforts to curtail anthropogenic emissions below intermediate levels (SSP2–4.5), climate model projections indicate a rapidly increasing risk of the PNW regularly experiencing 2021-like extreme summer temperatures, with a 50% chance of yearly occurrence by 2050. The 2021 summer temperatures experienced across the PNW provide a benchmark and impetus for communities in historically temperate climates to account for extreme heat-related impacts in climate change adaptation strategies.

Extreme temperatures are some of the most significant climate impacts that human populations currently experience6, but communities around the world have different levels of vulnerability and resilience to the consequences of climate change16,17. The timing and location of the PNW heatwave are particularly alarming, because none of the natural, socioeconomic, or infrastructural systems of the normally temperate PNW climate are currently adapted to prolonged extreme warmth. The inadequate regional infrastructure reflects a social perception that extreme warmth is not a substantial threat in this region of North America18. Prolonged heatwaves often go unrecognized as serious community health threats in temperate locations19, but when they do occur, indoor facilities are unable to provide heat relief for the most vulnerable populations. Compared to the US national average, significantly less homes in the PNW have primary air conditioning (AC)20. While rates of AC use in British Columbia, Canada have nearly doubled in the last decade, as of 2020, still less than 40% of British Colombians have centralized household AC21, indicating a persistent vulnerability to warm temperature extremes. In addition to the immediate societal and health consequences, the effects of sustained temperature stress on forest ecosystems are visible across much of the PNW22,23.

A growing body of literature, using limited observational data and modeling to characterize the historic nature of the 2021 PNW summer conditions, shows this event to be highly anomalous and of a magnitude with no comparable modern climatic analog24,25. Rapid attribution suggests that the occurrence of this event would have been virtually impossible without anthropogenic climate change, but because the observed extreme temperatures were so far outside the range of historically observed temperatures (since ca. 1895), it is difficult to confidently quantify the rarity of the event24. Augmenting the observational record with proxy data can be an effective strategy for decreasing uncertainties related to longer-term climate variability, thereby leading to improved characterization and contextualization of recent warming trends and extreme events. Further, characterizing temporal variation in the rates of environmental change including extreme events is critical to better constrain future impacts and inform strategies for immediate climate change adaptation.


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