The Alaskan Summer 2019 Extreme Heat Event: The Role of Anthropogenic Forcing, and Projections of the Increasing Risk of Occurrence

Abstract

Introduction BackgroundIn June and July, 2019, Alaska experienced an extended period of record high temperatures. Temperatures at several weather stations broke all-time records; in Anchorage, temperatures reached 32°C, breaking records by 3°C (Di Liberto, 2019). Temperatures remained abnormally high from approximately June 23-July 10, with Anchorage breaking 27°C for six consecutive days (another record).In Alaska, increasing temperatures have significant societal and economic effects: degrading permafrost can result in damages to roads and infrastructure as soils sink (Melvin et al., 2017), shifting marine ecosystems can cause serious damage to Alaska's vitally important fish and crab industry (Thorsteinson & Love, 2016), and increasing wildfire risk can pose risk to many communities (Young et al., 2017, Yu et al., 2021. The risk of highly active and damaging fire seasons such as in the summer of 2015 has been shown to have increased by 35%-60% due to anthropogenic forcing (Partain et al., 2016). Damages in Alaska due to human-induced climate change are expected to range from $110 to $270 million per year and will disproportionately affect Alaska's rural and Indigenous communities (Cochran et al., 2013;Gray et al., 2018). The extent of future warming and expected frequency of extreme heat events in the region are still uncertain, and thus it is vital to increase our understanding of observed events and improve our ability to quantify present and future climate risk. Extreme heat events have frequently been observed in Arctic regions in the last decade (Thoman & Brettschneider, 2016), likely the result of anthropogenic climate change. Observations can be used to quantify changes in temperature over the past several decades, while climate models can be used to project future warming-which may accelerate-and changes in frequency of extreme heat events. Studies analyzing observed climate identify clear warning signals over the Arctic at a faster rate than much of the planet; this polar Abstract Extreme heat occurred over Alaska in June-July 2019, posing risks to infrastructure, ecosystem, and human health. It is vital to improve our understanding of the causes of such events and the extent to which anthropogenic forcing may alter their likelihood and magnitude. Here, we use multiple large ensembles of climate models, comprising thousands of simulated years, to investigate these issues. Our results suggest that the presence of anthropogenic radiative forcing increased the likelihood of the 2019 extreme heat event by as much as 6%. Further we show the rate of occurrence of such an extreme heat event is likely to substantially increase in the future with increasing levels of atmospheric greenhouse gases. While uncertainty in projected climate risk from model choice leads to a broad range of future extreme heat event probabilities, some models project that with rapidly increasing levels of greenhouse gases the likelihood of such events would exceed 75% by 2090.Plain Language Summary An extended period of high temperatu...

Heatwaves Similar to the Unprecedented One in Summer 2021 Over Western North America Are Projected to Become More Frequent in a Warmer World

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Comparison of Climate Model Large Ensembles With Observations in the Arctic Using Simple Neural Networks

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