2012: Hottest Year On Record For United States

3:13 pm in Uncategorized by WeatherDem

After a brief hiatus (10 graduate school credits & TA-ing leaves no time for blogging), I’m back posting on FDL.  I expect to post much more regularly in 2013 as school activities ramp down.  More of my writing will also include a policy angle.  I want to do more to bridge the science and policy worlds in my blogging as well as in my future career.

It’s official: 2012 was indeed the hottest year in 100+ years of record keeping for the contiguous U.S. (lower 48 states).  The record-breaking heat in March certainly set the table for the record and the heat just kept coming through the summer.  The previous record holder is very noteworthy.  2012 broke 1998′s record by more than 1°F!  Does that sound small?  Let’s put in perspective: that’s the average temperature for thousands of weather stations across a country over 3,000,000 sq. mi. in area for an entire year.  Previously to 2012, temperature records were broken by tenths of a degree or so.  Additionally, 1998 was the year that a high magnitude El Niño occurred.  This El Niño event caused global temperatures to spike to then-record values.  The latest La Niña event, by contrast, wrapped up during 2012.  La Niñas typically keep global temperatures cooler than they otherwise would be.  So this new record is truly astounding!

The official national annual mean temperature: 55.3°F, which was 3.3°F above the 20th century mean value of 52°F.


Figure 1 – NOAA Graph showing year-to-date average US temperatures from 1895-2012.

This first graph shows that January and February started out warmer than usual (top-5), but it was March that separated 2012 from any other year on record.  The heat of July also caused the year-to-date average temperature to further separate 2012 from other years.  Note the separation between 2012 and the previous five-warmest years on record from March through December.  Note further that four of the six warmest years on record occurred since 1999.  Only 1921 and 1934 made the top-five before 2012 and now 1921 will drop off that list.


Figure 2 – Contiguous US map showing state-based ranks of 2012 average temperature.

Nineteen states set all-time annual average temperature records.  This makes sense since dozens of individual stations set all-time monthly and annual temperature records.  Another nine states witnessed their 2nd warmest year on record.  Nine more states had top-five warmest years.  Only one state (Washington) wasn’t classified as “Much Above Normal” for the entire year.  The 2012 heat wave was extensive in space and severe in magnitude.

Usually, dryness tends to accompany La Niña events for the western and central US.  This condition was present again in 2012, as the next figure shows:

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