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Wednesday, February 24, 2021

2020 Climate Review; Global and Alaska

 Unsurprisingly, the global climate in 2021 continued to warm and to experience climate-related disasters.  Global air temperature tied 2016 as the warmest year on record.  Oceans continued to warm, and marked the warmest year on record.  Oceans absorb about 95% of heating from greenhouse gases, and thus have a more consistent increase in temperature.  

According to Carbon Brief, CO2 emissions in 2020 fell by about 7% compared to 2019, due to economic cut-backs during the Covid-19 epidemic.  Nevertheless, average atmospheric CO2 ended the year at about 413.5 ppm, a rise of about 2.5 ppm over 2019 (ESRL/NOAA).  That rate of increase is not significantly different than the previous decade.  For reference, pre-industrial levels of CO2 were about 280 ppm.

Alaska had a relatively mild 2020 in terms of climate change, cooler than recent years, with temperatures in the range of temperatures of the 1980, but still warmer than earlier decades.  There were fewer climate-related wildfires, and the warm-water "blob" in the Gulf of Alaska did not develop during 2020. Nevertheless, the long-term trajectory of climate change in Alaska is still clear.

 Low soil moisture results in dry plants, which cause wildfires to burn hotter and faster.  Low soil moisture also causes dead undergrowth, which provides fuel-loading to forests, increasing fire danger.
Robert Rohde of Berkeley Earth prepared the chart above.  Annual averages of precipitation and temperature during the California fire season are shown in a color spectrum ranging from cool to warm colors representing 20-year intervals.  The chart shows a slow progression toward warmer temperatures, with the most significant change in the last twenty years.  Note that the ten largest wildfires, and the ten most destructive wildfires all occur in the warmest & driest quadrant of the chart.  The amount of change in the past 40 years is dramatic, and sobering if these trends continue over the next 40 years.

Alaska had a relatively moderate year regarding climate events in 2020.  Nevertheless, the long-term trends remain.  NOAA published a report card indicating that changes in the Arctic are likely to be permanent.

 The chart shows temperature change since 1945.
Arctic temperatures are rising two to three times faster than the rest of the globe, as a consequence of feedback factors from loss of snow and ice.  This effect was predicted in climate models by the Jasons' report in 1979.  Note also that air temperatures over land has warmed more than the oceans. 
Oceans absorb about 95% of heat retained by greenhouse gases.  The absorption of heat, and evaporative cooling, keeps air temperatures over oceans lower than over land.  Therefore, air temperatures over land are increasing faster than the global average, which is inconvenient, because we live on land.
Alaska temperatures clearly show the impact of Arctic amplification.  North Slope temperatures in the fall season have been sharply higher since the mid-1990s, due to early loss of Chukchi Sea ice.

Thunderstorms have become measurably more frequent near Fairbanks since about 1990.  The state's biggest wildfires typically occur near Fairbanks, and are most often caused by lightning.
Alaska's climate continues to change rapidly, and future decades are likely to bring serious, detrimental change.