In 118 years of U.S. records, July 2012 stands as king, hotter than any month previously observed. NOAA reports today that the average temperature across the continental U.S. was 3.3 degrees Fahrenheit warmer than the 20th century average, 0.2 degrees hotter than the previous record set in July, 1936.
Not only was the month of July unrivaled for its hot temperatures across the nation, but so too were the first seven months of the calendar year and the last 12 months. In fact, the last four 12-month periods have each successively established new records for the warmest period of that length.
In this most recent 12-month span from August 2011-July 2012, every state observed warmer than average temperatures except Washington state, which was near average.
During July, some of the hottest temperature occurred in the Plains, Midwest and Eastern Seaboard. Virginia had its hottest July on record, a full 4 degrees above average. Maryland’s July was 3rd hottest on record. In 32 of the 48 contiguous U.S. states, July ranked among the top 10 hottest. At least 35 cities/towns had their hottest day on record (any day of the year).
The hot weather was intimately linked to the drought, which expanded to nearly 63 percent of the Lower 48 in July. In a vicious cycle, high temperatures accelerated evaporation which dried up the land surface allowing it to heat up even more.
The worst of the drought centered in the Midwest and Plains. Nebraska, Iowa, Illinois, and Missouri had July precipitation totals ranking among their ten driest. NOAA said the area of the country in extreme to exceptional drought doubled from 10 percent in June to 22 percent in July. The drought reached the most extensive levels since December 1956.
The hot and dry conditions also stoked blazing wildfires, which consumed more than 2 million acres in July. That's a half a million acres above average, and the fourth most on record since 2000.
Links to climate change?
2012 has proven to be an exceptionally warm year in the U.S. More daily record high temperatures have already been set or tied (with 5 months remaining) than during 2011 in its entirety. There have been about 10 times as many record highs as record lows.
When considering connections to global warming and increasing concentrations of greenhouse gases, it’s important to recognize the area of the U.S. represents less than 4 percent of the globe and 2012 is just one year in a long history.
Having said that, global temperatures have also been running warm. While NOAA’s global report for July temperatures has not yet been issued, June ranked 4th warmest on record globally and marked the 328th consecutive month of above average temperatures.
As global temperatures have been elevated for some time and long-term averages are rising, it’s likely the same influences acting on global temperatures are also affecting temperatures on smaller scales.
In other words, increasing greenhouse gas concentrations are probably increasing the odds of these exceptionally warm years/months wherever one resides.