365 Days of Climate Awareness 122 – Extreme Weather Events: Extreme Heat

 

The IPCC’s Sixth Assessment Report, Working Group 1: The Physical Science Basis (AR6-WG1) minces no words about the scale and imminence of the climate threat. Chapter 11 is devoted to extreme weather events, including heat waves. “The frequency and intensity of hot extremes have increased and those of cold extremes have decreased on the global scale since 1950.”

June 27, 2021 temperature anomaly relative to 2014-2020 average.

“Human-induced greenhouse gas forcing is the main driver of the observed changes in hot and cold extremes on the global scale (virtually certain) and on most continents (very likely)…[t]he frequency and intensity of hot extremes will continue to increase and those of cold extremes will continue to decrease, at both global and continental scales and in nearly all inhabited regions with increasing global warming levels…On the global scale, evidence of an increase in the number of warm days and nights and a decrease in the number of cold days and nights, and an increase in the coldest and hottest extreme temperatures is very robust and consistent among all variables.”

There are several recent and frightening examples of high temperatures disrupting huge regions and killing both people and animals. These include the June 2021 heat wave in western North America, classified as a 1000-year event, which spanned from New Mexico, east to Utah and along the coast north to British Columbia. It is estimated to have killed over 2200 people in the United States and Canada, and left the Pacific Northwest in flames throughout July. From 2019 into 2020, Australia's worst-ever fire season burned more than 46 million acres, left an estimated 3 billion animals dead or displaced, with some endangered species perhaps driven extinct. The fires killed almost 500 people directly or from smoke inhalation and impacted air quality throughout all southeastern Australia.

Artists's rendition of the cumulative wildfires of Australia, 2020.

Marine heat waves also occur, though the drivers for those are more complicated, involving atmosphere-ocean interaction and ocean circulation. These include oscillations like ENSO, which itself is a joint ocean/atmosphere cycle. But a number of long—up to five years—and intense oceanic heat waves have been observed around the world in recent years, such as off the US west coast and the Caribbean, and they are highly destructive of local marine life. Coral reefs globally suffer from elevated temperatures, which (among other causes) forces them to bleach. The frequency and intensity of worldwide bleaching events has increased in recent decades.

Tomorrow: precipitation.

Be brave, and be well.