"Dark Side of Climate Change" Seen in Record Setting Night-Time Temperatures in 37 U.S. States in Summer Of 2010

Special risk seen to elderly, low-income population from reduced overnight cooling; Night-time temperatures more sensitive to greenhouse gas emissions.

Records Set in AL, AZ, AR, CT, DE, FL, GA, IL, IN, IA, KS, KY, LA, ME, MD, MA, MI, MN, MS, MO, NH, NJ, NM, NY, NC, ND, OH, OK, PA, RI, SC, SD, TN, TX, VA, WV, and WI.

WASHINGTON, D.C.(September 16, 2010) -- While many Americans focused on this summer’s day-time record-setting temperatures, there is growing concern about the largely ignored pattern of record-setting night-time temperatures, which pose special dangers to elderly and low-income Americans who are more dependent on overnight cooling during the hottest months.

A new analysis from the Natural Resources Defense Council (NRDC) shows that:

  • At nearly one of four weather stations in the contiguous United States -- 278 out of 1,218 -- the average night-time low temperatures for June, July and August 2010 were hotter than at any time since 1895.
  • Considering all 513 weather stations east of the Mississippi, 40 percent reported their hottest average night-time low temperatures on record and more than 80 percent reported average nighttime low temperatures among their five hottest on record in summer 2010.
  • More than half of all U.S. weathers stations recorded average night-time low temperatures among their five hottest on record.
  • Record night-time temperatures were set at stations in 37 states: Alabama, Arizona, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Virginia, West Virginia, and Wisconsin. 

 Dan Lashof, director, Climate Center, Natural Resources Defense Council, said:  “Welcome to what might be termed ‘the dark side of climate change.’   Summer 2010 was the hottest on record in many locations in the United States. Not only was it hot during the day, but it didn’t cool off at night. While one hot summer does not prove that global warming is happening, the long-term global trend does, according to the U.S. National Academy of Sciences, among others. The long, hot summer of 2010 follows the hottest decade on record and more record high temperatures can be expected in the future as heat-trapping pollution continues to build up in our atmosphere.”

Night-time temperatures are more sensitive to the buildup of heat-trapping pollution in the atmosphere than daytime temperatures because increases in atmospheric aerosols and cloud cover have counteracted some of the warming effect of greenhouse gases during the day.

Kim Knowlton, senior scientist, Health and Environment Program, Natural Resources Defense Council, said:  “Hot, stagnant nights can prove even more harmful than daytime highs as vulnerable populations --particularly the elderly and low-income individuals without air conditioning -- are unable to cool down and get relief from the stress of day-time heat that persists into the evening.”

The NRDC analysis highlights the following states:

  • In Maryland, 12 of the 16 stations in the Historical Climatology Network reported their hottest average nighttime low temperatures on record in summer 2010. All 16 Maryland stations reported average nighttime low temperatures among their five hottest on record in summer 2010.
  • In Florida,   nearly all -- 21 of 22 -- weather stations reported average nighttime low temperatures among their five hottest on record in summer 2010.
  • The Midwest also experienced very warm nighttime temperatures. In Illinois and Indiana, 92 percent and 86 percent of the stations, respectively, reported average nighttime low temperatures among their five hottest on record in summer 2010.
  • The Western United States was not as hot as the Eastern half of the country. Nonetheless, seven stations in Arizona reported average temperatures for this summer among their five hottest on record, and 11 stations in New Mexico reported average nighttime low temperatures among their five hottest.

The analysis also points out that: “Record-high temperatures are not the only weather extremes we have seen in 2010. Because the atmosphere can hold more moisture as it warms, there is more rapid evaporation when it is dry and more intense rainfall when it is wet. The result is an increase in severe droughts and floods. As we have seen in Russia, Pakistan, China, and the United States, the results have been tragic. Russia has seen hundreds of wildfires and thousands of deaths in Moscow during its worst heat wave on record. In Pakistan more than a thousand people have been killed, and a million more displaced by floods. Flooding this year has also killed more than a thousand people in China, and more than 50 in Iowa and Tennessee.”

To read the full analysis, please go to http://www.nrdc.org/globalWarming/hottestsummer/.

EDITOR’S NOTE: A streaming audio replay of the news event will be available on the Web at http://www.nrdc.org/globalWarming/hottestsummer/ as of 3 p.m. EDT on September 16, 2010.