Thanks to a record warm January-to-June period and intense, long-lasting heat waves during March, June, and July, the U.S. has passed an ominous milestone: with about five months remaining in the year, there have already been more record daily high temperatures set or tied so far this year than were set or tied during all of 2011. And 2011 had the second-warmest summer on record for the lower 48 states.
Graphic showing how record daily highs have outnumbered record daily lows during recent decades, as the average climate has warmed during the period. Click on image for a larger version.
Credit: Climate Central.
According to Guy Walton of The Weather Channel, who compiles temperature record statistics using data from the National Climatic Data Center, there were 26,674 daily record highs broken or tied during 2011, and through August 5 there were 27,042 records broken or tied this year. The March and July heat waves clearly gave 2012 the edge over last year. During March alone, 7,755 daily records were set or tied, and 4,420 records were broken or tied during July. (You can track temperature records using Climate Central’s Record Tracker.)
That this year has already eclipsed the number of records set during 2011 is especially remarkable because 2011 was a very warm year, during which Oklahoma set the record for the all-time warmest average summer temperature of any state in the country, with Texas coming in a close second thanks to the drought conditions and heat waves there. Both states have been baking under searing heat once again this summer. Oklahoma City reached 112°F on July 1 and 2, and 113°F on the 3rd, which tied the all-time high temperature record for that location. Every day from July 18 through August 4 reached or exceeded 100°F in Oklahoma City, and the heat and drought have led to an outbreak of wildfires across the state.
While the final four months of the year may not seem like they would add much to the record totals, during 2010, there were 8,636 record daily highs set or tied from September through the end of December, and in 2011 the total was 5,800.
March 2012 was an especially warm month in the lower 48 states, as this map of temperature departures from average shows. Click on image for a larger version.
Credit: High Plains Regional Climate Center.
Last year, record daily high temperatures outnumbered record daily lows by a ratio of about 3-to-1. This year, that ratio is even more lopsided, favoring high-temperature records by a ratio of about 10-to-1.
Climate research indicates that over longer timescales, these ratios are increasingly favoring warm records as well. A study published in 2009 found that rather than a 1-to-1 ratio, as would be expected if the climate were not warming, the ratio was closer to 2-to-1 in favor of warm temperature records during the past decade (2000-2009). This finding cannot be explained by natural climate variability alone, the study found, and is instead consistent with global warming.
The study used computer models to project how the records ratios might shift in future decades as the amount of greenhouse gases in the air continues to increase. The results showed that the ratio of daily record highs to daily record lows in the lower 48 states could soar to 20-to-1 by mid-century, and 50-to-1 by 2100.