CLIMATE: U.S. temperature study shows accelerated warming in recent decades

Posted at 8:33 AM, Jun 13, 2012

RICHMOND, Va. (WTVR) – A new study by scientists working with Climate Central delves into the temperature trends of the United States, not only as a whole, but also by breaking it down state-by-state. Scientists and “amateur weather observers” alike have long-known that temperature changes over time vary from region to region, and can significantly be influenced by factors like natural variability, local geographic influences, the urban heat island effect, and air pollution. Contributing scientists to this study include Claudia Tebaldi, PhD, Dennis Adams-Smith, and Nicole Heller, PhD.  This focused approach investigated average daily temperatures in the Lower 48 states from 1912 to the present, and then compared that to more recent decades from 1970 to the present. This daily surface temperature data is from the National Climatic Data Center’s U.S. Historical Climatology Network of weather stations.

The report begins, “Global warming isn’t uniform. The continental U.S. has warmed by about 1.3°F over the past 100 years, but the temperature increase hasn’t been the same everywhere: some places have warmed more than others, some less, and some not much at all.”

Their conclusions are as follows:

  • Over the past 100 years, the top 10 states on average warmed 60 times faster than the bottom 10 (0.26°F per decade vs. 0.004°F per decade), when looking at average mean temperatures. During this timeframe, 45 states showed warming trends, although 21 were not statistically significant. Three states experienced a slight cooling trend.
  • Since 1970, warming began accelerating everywhere. The speed of warming across the lower 48 more than tripled, from 0.127°F per decade over the 100-year period, to 0.435°F per decade since 1970. In the last 42 years the 10 fastest-warming states heated up just twice as fast, not 60 times as fast as the 10 slowest-warming states (0.60°F vs. 0.30°F per decade). Over the past 42 years 17 states warmed more than half a degree F per decade.
  • The states that have warmed the most — whether you look at the past 100 years or just the past 40 —include northern-tier states from Minnesota to Maine and the Southwest, particularly Arizona and New Mexico. Places that have warmed the least include Southeast states, like Florida, Alabama, Georgia and South Carolina, along with parts of the central Midwest, like Iowa and Nebraska.

Climate Central, The Heat Is On: U.S. Temperature Trends

For Virginia since 1912, our state has experienced a temperature change of +0.107°F per decade, ranking 29 among the other Lower 48 states. Arkansas, Georgia, and Alabama were the only states with a cooling trend during this time-frame.

Map: Climate Central

When looking at the past several decades, though, every single state in the Lower 48 has experienced a warming trend. In Virginia, the temperature change is +0.456°F per decade, ranking 24 among the other Lower 48 states.

Map: Climate Central

Even though each state is warming at different rates, since 1970 every state “has seen a significant warming trend,” according to the report. Virginia is among one of the states warming faster than the national average since 1970.

Map: Climate Central

Click on the interactive map below to explore more:

This report does not point to any single cause for these trends, other than mentioning previously studied factors like the regional influences of large bodies of water on temperature trends (coastal states), aerosol pollutants, and natural climate variability, but instead concludes with the following statement by the three scientists:
“We do not expect that future trends will be a simple extrapolation of current patterns, since natural variability and the future emissions–of both heat-trapping greenhouse gases and cooling aerosol pollutants–will shape future rates of warming. The rates of warming we’ve seen in various regions of the U.S. could be different in the future from what they’ve been in the past.”

Meteorologist Carrie Rose
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