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2020 Ends Hottest Decade on Record: Decadal Temperature Chart as Iconic as CO2 Keeling Curve

, senior climate scientist | January 15, 2021, 3:58 pm EST
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It is now official, 2020 ends the hottest decade on record. The top takeaway is the decadal temperature chart has now become as iconic as the “Keeling Curve,” which has recorded atmospheric carbon dioxide at Mauna Loa Observatory in Hawaii since 1958, and shows a similar upward trend.

Global Decadal Average Temperature

This warmest decade was preceded by the second warmest, which in turn was preceded by the third warmest, which in turn was preceded by the fourth warmest decade, meaning the last 40 years, on average, have been the hottest on record.  The pace of heat-trapping emissions from fossil fuel burning and other human activities has not yet slowed this upward trend. Quite the opposite.

Decadal data by definition looks at long-term trends, so we’ll have to wait another decade before another bar can be added to the temperature chart.  In the meantime, headlines are tracking how 2020 stacked up on the annual ranking.

2020 Global Annual Average Temperature

Independent analyses around the world use slightly different baseline reference periods and approaches to determine the global annual temperature. Given the confidence range for the final number this often yields slightly different rankings between institutions. No matter how you slice it, 2020 was hot!

NASA (USA) and Copernicus (EU) report 2020 as tied with 2016 as the warmest year and NOAA (USA) reported 2020 as the second warmest in their 141-year record. All the more remarkable since an ocean cycle phase in the Pacific Ocean–La Niña–tended to pull down temperatures toward the end of 2020.

Since this number is a combined land and ocean average, it is worth taking a closer look at where the warmth was most notable in 2020.  For this we will report the NOAA Global Climate Report – Annual 2020 rankings which uses the 20th century average for their baseline. 

Breakdown of 2020 land and ocean surface temperature:

 Warmest years:

  • The seven warmest years in the 1880–2020 record have all occurred since 2014.
  • The 10 warmest years have occurred since 2005.
  • 2020 is the 44th consecutive year (since 1977) above the 20th century average.

Hemispheres:

  • 2020 Northern Hemisphere was the warmest in the 141-year record.
  • 2020 Southern Hemisphere was the fifth warmest on record.

Oh yes, and where most of us live–on the global land surface area–ranked as the warmest on record.  Since the industrial revolution, the United States has contributed the most to the rise in global average temperature. Rejoining the Paris Climate Agreement would be a welcome commitment to reducing emissions.

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Data Plots from NOAA and Scripps Institution of Oceanography

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