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Fall Is Getting Warmer Due To Climate Change

A warming fall season means that summer mosquitoes, sweltering heat, wildfires, and allergies are sticking around longer.
Madison has seen an average temperature increase of 2.7 degrees during the fall time season...
Madison has seen an average temperature increase of 2.7 degrees during the fall time season since 1970.(WMTV)
Published: Oct. 2, 2021 at 7:53 AM CDT
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MADISON, Wis. (WMTV) - The calendar may say it’s fall, but conditions over the past couple of weeks have felt more like summer. A trend that will likely become the new normal as we move forward in time. While many may be enjoying the warmer weather lasting later into the fall season, it isn’t all good news.

A LOOK AT THE TRENDS:

Our partners at Climate Central analyzed 51 years of fall temperature data in 246 U.S. locations and here is what was found.

  • Average temperatures are rising: Among the 246 cities analyzed, 95% (234) experienced an increase in average fall temperatures since 1970. And 57% (134) of those cities experienced warming of at least 2°F.
  • Warming is fastest in Texas and the Southwest Region: The five greatest increases are seen in Reno, Nev. (7.6°F), Las Vegas (6°F), El Paso, Tex. (5.6°F), Tucson, Ariz. (5.4°F), and Phoenix (5.3°F).
  • There are more fall days above normal: Of the 246 locations, 68% (167) recorded at least seven additional days above their normal fall average temperature since 1970. Nine of these cities saw an extra month of above-average temperatures. For the second year in a row, Reno, Nev. tops the list with 43 additional days.
  • Fall has a new ‘normal’: NOAA’s climate normals are 30-year averages of climate variables which serve as a reference point for comparing current weather to a given location’s ‘normal’ climate. Fall mean temperature normals have increased across most of the contiguous U.S. between the current period (1991-2020) and the previous period (1981-2010). Some of the largest differences were found in the Southwest and Northeast, exceeding 1°F at some locations.

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When we take a look at data on a more local level, we can see a later “first” date of cooler temperatures with the new climate normal’s being released this year. While only a couple days later for most dates, it can be significant and is part of the much larger warming problem across the globe.

Madison is now averaging 12.3 more days above normal during the fall time season, September-November, than it did back in 1970. This equates to an average temperature increase of 2.7 degrees!

Madison is seeing an average of 12.3 more days above normal during the fall time season than it...
Madison is seeing an average of 12.3 more days above normal during the fall time season than it did back in 1970.(WMTV)
Most of the country has seen a warming trend during the fall season since 1970. This trend is...
Most of the country has seen a warming trend during the fall season since 1970. This trend is especially pronounced across the western half of the country.(WMTV)

FALL IS WARMING. SO WHAT?

HOW A WARMER FALL WILL AFFECT COOLING DEMANDS:

With a warmer fall season, some regions are relying on air conditioning for longer. The EIA projects that air conditioning demand will be responsible for the greatest increase in residential and commercial energy through 2050. This costs American homeowners $29 billion annually. Cooling demand is threatened by power outages caused by extreme weather events like the concurrent hurricane season. See Poweroutages.us which tracks, records and aggregates power outage data across the U.S. in an informative and up-to-date map.

HOW A LONGER MOSQUITO SEASON IMPACTS PUBLIC HEALTH:

An increase in fall heat and humidity encourages mosquitos to linger for longer. Mosquitos aren’t just itchy nuisances: they carry serious diseases like the West Nile Virus and Dengue Fever. The Centers for Disease Control and Prevention (CDC) provides county-level maps which show case numbers by disease and year. See Climate Central’s 2020 analysis of mosquito-suitable days for more on growing conditions and long-term trends.

METHODOLOGY

Fall (September through November) trends were calculated using data from the Applied Climate Information System from 1970-2020. Fall days above normal are relative to the 1991-2020 NCEI climate normal. Changes in average temperature since 1970 for US climate divisions were calculated using data from NOAA/NCEI. Displayed trend lines on city analysis are based on a mathematical linear regression. Climate Central’s analyses include 247 cities, however, only 246 stations are included due to large data gaps in Wheeling, W. Va.

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