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									Recent Climate Change - Temperature Changes | Science | Climate Change | U.S. EPA                                                   3/20/09 5:43 PM

                                                                                         Last updated on Wednesday, December 17th, 2008.
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    Temperature Changes
                                                                                                                    Related Links
    Surface Temperature Change | Tropospheric Temperature Change |
                                                                                                            EPA: Future Temperature
    Stratospheric Temperature Change | Recent Scientific Developments                                       Changes
                                                                                                            CCSP: Product 1.1 -
    Temperatures are changing in the lower atmosphere - from the Earth’s
                                                                                                            Temperature Trends in the
    surface all the way through the stratosphere (9-14 miles above the                                      Lower Atmosphere Steps for
    Earth’s surface). Scientists are working to document temperature trends                                 Understanding and Reconciling
    and determine their causes.                                                                             Differences
                                                                                                            NASA: Global Institute for
    Surface Temperature Change                                                                              Space Studies Surface
                                                                                                            Temperature Observations
                                                                             Records from land          NOAA 2007 State of the
                                                                             stations and ships         Climate
                                                                             indicate that the global
                                                                             mean surface
                                                                             temperature warmed by between 1.0 and 1.7°F since
                                                                             1850 (see Figure 1). These records indicate a near
                                                                             level trend in temperatures from 1880 to about 1910,
                                                                             a rise to 1945, a slight decline to about 1975, and a
                                                                             rise to present (NRC, 2006). The Intergovernmental
                                                                             Panel on Climate Change (IPCC) concluded in 2007
      Figure 1: Annual Average Global Surface                                that warming of the climate system is now
      Temperature Anomalies 1880-2006.
      Courtesy NOAA (Surface temperature                                     “unequivocal,” based on observations of increases in
      records such as the one shown here have                                global average air and ocean temperatures,
      been quality controlled to remove the                                  widespread melting of snow and ice, and rising global
      effects of urbanization at observing stations                          average sea level (IPCC, 2007).
      in and around cities.
      Click on Thumbnail for full size image.
                                                    According to the National Oceanic and Atmospheric
    Administration's (NOAA) 2007 State of the Climate Report and the             United States Surface
    National Aeronautics and Space Administration's (NASA) 2007 Surface          Temperature Trends
    Temperature Analysis:                                                     Observations compiled by
                                                                                                            NOAA’s National Climatic Data
               Since the mid 1970s, the average surface temperature has                                     Center indicate that over the
               warmed about 1°F.                                                                            past century, temperatures
               The Earth’s surface is currently warming at a rate of about                                  rose across the contiguous
               0.32ºF/decade or 3.2°F/century.                                                              United States at an average
               The eight warmest years on record (since 1850) have all                                      rate of 0.11°F per decade
               occurred since 1998, with the warmest year being 2005.                                       (1.1°F per century). Average
                                                                                                            temperatures rose at an
    Additionally (from IPCC, 2007):                                                                         increased rate of 0.56°F per                                                                                   Page 1 of 3
Recent Climate Change - Temperature Changes | Science | Climate Change | U.S. EPA                         3/20/09 5:43 PM

                                                                                    decade from 1979 to 2005.
               The warming trend is seen in both daily maximum and minimum          The most recent eight-, nine-,
               temperatures, with minimum temperatures increasing at a faster       and ten-year periods were the
               rate than maximum temperatures.                                      warmest on record.
               Land areas have tended to warm faster than ocean areas and
                                                                                    Warming occurred throughout
               the winter months have warmed faster than summer months.
                                                                                    most of the U.S., with all but
               Widespread reductions in the number of days below freezing
               occurred during the latter half of the 20th century in the United    three of the eleven climate
               States as well as most land areas of the Northern Hemisphere         regions showing an increase
               and areas of the Southern Hemisphere.                                of more than 1°F since 1901.
               Average temperatures in the Arctic have increased at almost          The greatest temperature
               twice the global rate in the past 100 years.                         increase occurred in Alaska
                                                                                    (3.3°F per century). The
    The IPCC has concluded that most of the observed warming in global              Southeast experienced a very
    average surface temperature that has occurred since the mid-20th                slight cooling trend over the
                                                                                    entire period (-0.04°F per
    century is very likely a result of human activities (IPCC, 2007). During
                                                                                    century), but shows warming
    the first half of the last century, there was likely less human impact on       since 1979.
    the observed warming, and natural variations, such as changes in the
    amount of radiation received from the sun, likely played a more
    significant role.

    Tropospheric Temperature Change

    Measurements of the Earth’s temperature taken by weather balloons
    (also known as radiosondes) and satellites from the surface to 5-8 miles
    into the atmosphere - the layer called the troposphere - also reveal
    warming trends. According to NOAA's National Climatic Data Center:

               For the period 1958-2006, temperatures measured by weather
               balloons warmed at a rate of 0.22°F per decade near the surface      Figure 2: Annual Mean
               and 0.27°F per decade in the mid-troposphere. The 2006 global        Temperature Anomalies 1901-
               mid-troposphere temperatures were 1.01°F above the 1971-             2005. Click on Thumbnail for
               2000 average, the third warmest on record.                           full size image. Data courtesy
               For the period beginning in 1979, when satellite measurements        NOAA's National Climatic Data
               of troposphere temperatures began, various satellite data sets       Center.
               for the mid-troposphere showed similar rates of warming —
               ranging from 0.09°F per decade to 0.34°F per decade,
               depending on the method of analysis.

    Stratospheric Temperature Change

    Weather balloons and satellites have also taken temperature readings in the stratosphere – the layer
    9-14 miles above the Earth’s surface. This level of the atmosphere has cooled. The cooling is
    consistent with observed stratospheric ozone depletion since ozone is a greenhouse gas and has a
    warming effect when present. It’s also likely that increased greenhouse gas concentrations in the
    troposphere are contributing to cooling in the stratosphere as predicted by radiative theory (Karl et al.,

    Recent Scientific Developments

    The U.S. Climate Change Science Program (CCSP) recently published the report “Product 1.1
    Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences,”
    which addresses some of the long-standing difficulties in understanding changes in atmospheric
    temperatures and the basic causes of these changes. According to the report:

               There is no discrepancy in the rate of global average temperature increase for the surface                                                         Page 2 of 3
Recent Climate Change - Temperature Changes | Science | Climate Change | U.S. EPA                      3/20/09 5:43 PM

               There is no discrepancy in the rate of global average temperature increase for the surface
               compared with higher levels in the atmosphere. This discrepancy had previously been used to
               challenge the validity of climate models used to detect and attribute the causes of observed
               climate change.
               Errors identified in the satellite data and other temperature observations have been corrected.
               These and other analyses have increased confidence in the understanding of observed climate
               changes and their causes.
               Research to detect climate change and attribute its causes using patterns of observed
               temperature change shows clear evidence of human influences on the climate system due to
               changes in greenhouse gases, aerosols and stratospheric ozone.
               An unresolved issue is related to the rates of warming in the tropics. Here, models and theory
               predict greater warming higher in the atmosphere than at the surface. However, greater
               warming higher in the atmosphere is not evident in three of the five observational data sets
               used in the report. Whether this is a result of uncertainties in the observed data, flaws in
               climate models, or a combination of these is not yet known.

               IPCC, 2007: Climate Change 2007: The Physical Science Basis.                  Contribution of
               Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate
               Change [Solomon, S., D. Qin, M. Manning (eds.)].
               National Research Council (NRC), 2006. Surface Temperature Reconstructions For the Last
               2,000 Years.               National Academy Press, Washington, DC.
               Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling
               Differences. Thomas R. Karl, Susan J. Hassol, Christopher D. Miller, and William L. Murray,
               editors, 2006. A Report by the Climate Change Science Program and the Subcommittee on
               Global Change Research, Washington, DC.                                                      Page 3 of 3

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