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Measuring climate change as NOAA updates definition of ‘climate normals’

By David Pendered

The headline on a climate report from Yale Climate Connections says a lot: “What’s ‘normal’ in a changing climate?”

ivy growth

The invasive English ivy spreads swiftly in the warm, moist climate that has begun extending from daytime into overnight hours in Atlanta, according to a NOAA report. Credit: David Pendered

The story looks at upcoming revisions to federal database that’s used to determine if temperatures are warmer than “normal” and to make other weather comparisons. TV meteorologists use this database to say if a day is to be hotter than average.

NOAA is adopting a new time frame for its 30-year database of “normal.” NOAA is dropping the decade of 1981-1990 and adding the decade 2011-2020. By May, the new database is to be in place.

The wrinkle is that the past decade has been warmer and wetter than the one it’s replacing, according to YCC’s report, Updated yardstick begs question: What’s ‘normal’ in a changing climate? The report observes:

  • “For the contiguous U.S., the period 1991-2020 was roughly 0.44°F warmer and 0.34″ wetter than in 1981-2010, based on national-scale data published by NOAA’s National Centers for Environmental Information (NCEI). The final station-by-station data are scheduled to be released this spring.”
NOAA climate normals

NOAA’s climate report from a station at Atlanta’s airport shows the changes in daytime and overnight temperatures that occurred in the recent past. Credit: ncdc.noaa.gov

YCC posted the story Feb. 3 by Bob Henson, a Colorado-based meteorologist who wrote The Thinking Person’s Guide to Climate Change and last year concluded a five-year run co-producing the Category 6 site for Weather Underground.

UGA’s Pam Knox reviewed Henson’s material and generally concurs with his analysis, according to her Feb. 3 report on the website, Climate and Agriculture in the Southeast, which is sponsored by the UGA Cooperative Extension. Knox directs the UGA Weather Network and serves as agricultural climatologist. Knox observed:

  • “From the maps in the article, you can see that most of the Southeast will appear to be getting warmer and wetter compared to the previous normal period.”

Knox contributed to Henson’s research and he quotes a few lines from an email:

  • “Likewise, University of Georgia climatologist Pam Knox described her state’s temperature changes in an email: ‘Generally getting warmer, with more increases in minimum temperature than maximum temperatures (related to higher humidity and urbanization).’”
rain on windshield

Blinding rain is a sign of the wetter climate in Georgia that a UGA report says has become common over the past 30 years. Credit: David Pendered

The temperature values Knox cites are borne out in a report from NOAA on supplemental temperature normals. The report can be organized by state and by the field station within a state that provides the weather data. The report from Atlanta’s airport shows the following highs and lows for two selected months.

The chart shows the normal daytime high in January rose 1 degree from the normal for 1981-2010 (52.3 degrees) to 2006-2010 (53.3 degrees). The high in August rose 2.2 degrees from 1981-2010 (88.1 degrees) to 2006-2010 (90.3 degrees).

Regarding overnight lows, the chart shows the normal low rose by 0.6 degree from the normal for 1981-2010 (34.3 degrees) to 2006-2010 (34.9 degrees). The low in August rose 1.3 degrees, from 1981-2010 (70.7 degrees) to 2006-2010 (72 degrees).

Henson explores how the change in reporting periods factors into the discussion over climate changes in a section that begins:

  • “Each update of climate normals brings up another question: Does this practice serve as an inadvertent smokescreen, one that keeps us from fully seeing the relentless march of human-caused warming?”

Henson offers this observation in his concluding remarks:

  • “Of course, the atmosphere doesn’t care how we measure its warming. The absolute temperature increase is the same no matter what we use to assess ‘above’ and ‘below’ normal.”


David Pendered

David Pendered, Managing Editor, is an Atlanta journalist with more than 30 years experience reporting on the region’s urban affairs, from Atlanta City Hall to the state Capitol. Since 2008, he has written for print and digital publications, and advised on media and governmental affairs. Previously, he spent more than 26 years with The Atlanta Journal-Constitution and won awards for his coverage of schools and urban development. David graduated from North Carolina State University and was a Western Knight Center Fellow.


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  1. Mark February 8, 2021 8:48 am

    The 5th paragraph report’s error – “1991-2020 was 44 F warmer.” We would be roasting!Report

    1. David Pendered February 8, 2021 5:26 pm

      Hello, Mark,
      Good catch. Thank you!


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