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News :: Environment
July 2005 Warmest Month on Record for Northern Hemisphere
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20 Aug 2005
by Michael T. Neuman
Email: mtneuman (at) juno.com (unverified!)
17 Aug 2005
Modified: 08/17 12:03 CDT
Global warming continued in July 2005 with temperatures in the U.S. averaging 1.5 Fahrenheit (F) above the average temperature for July, over the period of record 1895-2004. Nine states had "much above normal" temperature for the month, an additional 33 states had "above average" temperatures, while only 6 states in the contiguous U.S. had near average temperature for the month. Wisconsin had above average temperatures, as did Alaska. No state was cooler than average for July.
Over 200 cities in the U.S. broke their daily high temperature records in July, with Denver, Colorado, having its second warmest July since 1872, and equaling the all-time highest daily temperature record of 105 F.. Las Vegas equaled its all-time record daily maximum temperature of 117 F, and had 5 consecutive days with temperatures exceeding 115 F.. Death Valley had 6 consecutive days (July 14-19) with high temperatures above 125°F (51.7°C). At least 13 deaths were blamed on the heat wave in Arizona.
The Northern Hemisphere had the highest geographically averaged monthly temperature on record, surpassing the previously hottest month of July 2002. The continent-wide average temperature this July over North America was 1.75 degrees F. above the average July temperature (for the period 1985-2004).
Meanwhile, the Northern Hemisphere's "sea ice extent" was lowest on record for the month of July at 9.02 million square kilometers. The July sea ice extent has remained below the long-term (1979-2000) going back to July 1997.
The month of July 2005 turned out to be the 2nd warmest July on record for the earth as a whole, exceeded only by the record warm July in El Nino year 1998. Warmer than average conditions in July were recorded in Scandinavia, much of Asia, North Africa, the United States, Mexico, Europe, Algeria, South Africa, Siberia and eastern Australia. Ocean temperatures were also 2nd highest on record. NOAA's National Climate Data Center (NCDC) calculates globally averaged monthly temperatures by processing data from thousands of world-wide observation sites on land and sea each month. Global average temperatures have been warmer than the 1971-2000 average temperatures for 121 straight months, going back to May 1995.
Selected NCDC prepared graphs of much of the above information follow:
Globally Averaged Land and Ocean Temperatures - 1880-2005 http://www.ncdc.noaa.gov/img/climate/research/2005/jul/glob_jul_pg.gif
Land Surface Temperatures - July 2005
Sea Surface Temperatures - Week of August 10, 2005 http://www.ncdc.noaa.gov/img/climate/research/sst/wksst.20050810.gif
NOAA's TIROS-N polar-orbiting satellites have been monitoring temperatures of the mid-troposphere, located approximately 2-6 miles above the Earth's surface, and the lower stratosphere, covering an altitude range of about 9-12 miles, since 1979. NOAA's analysis of the satellite record indicates that global temperatures are rising in the mid-troposphere, with July 2005 showing the 2nd warmest temperatures on record, undoubtedly a response to the rising concentrations of greenhouse gases in the troposphere from humans burning fossil fuels.
Temperatures in the lower stratosphere, on the other hand, have been significantly lower in the last 10-15 years than they were prior to the early 1990s.
[The large increase in stratospheric temperature readings in 1982 was caused by the volcanic eruption of El Chichon in Mexico, and the increase in 1991 was a result of the eruption of Mt. Pinatubo in the Philippines.]
Declining temperatures in the stratosphere are believed to be the result of:
(1) increased trapping of heat in the lower troposphere by the increased volumes of greenhouse gases, which results in less radiated heat from the surface rising into the stratosphere;
(2) the reduced quantity of ozone (a greenhouse gas) in the stratosphere, caused by ozone-depleting chemicals (CFCs).
With the exception of certain areas where there are "holes" in the ozone layer, the natural volume of ozone in the stratosphere presently absorbs much of the harmful solar ultraviolet radiation that bombards the earth. In the process of absorbing the solar radiation, the stratosphere warms up. It follows, therefore, that if the volume of ozone in the stratosphere is depleted by ozone-depleting chemicals, the stratosphere's temperature will decline even further.
A problem of increasing significance is that the cooler stratospheric temperatures chemically promote chlorine-caused depletion of ozone in the lower stratosphere, which leads to thinning of the ozone layer. As the ozone layer thins, more of the harmful solar ultraviolet radiation gets through the ozone layer, thus increasing the potential for skin cancer, eye damage and other health problems associated with increased human exposure to solar ultraviolet radiation.
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