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    ... A Warming World December 2005 Kevin E. Trenberth Top climate news 2005
    Message 1 of 1 , Dec 2, 2005
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      ---------- Forwarded Message ----------
      A Warming World
      <http://www.geotimes.org/current/feature_climate.html>
      <http://tinyurl.com/9kzw6>
      December 2005
      Kevin E. Trenberth

      Top climate news 2005

      Our planet is warming. The years 2002 to 2004 are the second, third
      and fourth warmest years since 1861 (1998 remains the warmest) and
      nine of the last 10 years (1995 to 2004) � the exception being 1996 �
      are among the 10 warmest years. Based on reconstructions of
      temperatures from proxy data, such as tree rings and ice cores,
      several studies have also concluded that northern hemisphere surface
      temperatures are warmer now than at any time in at least the last
      1,000 years.

      <http://www.geotimes.org/current/climate_tropo.jpg>
      Scientists this year published work that reconciles past errors in
      temperature measurements of the lower atmosphere, or troposphere, the
      top boundary of which is shown here at the division between the
      orange- and blue-colored bands of atmosphere. The research shows an
      overall warming trend in the troposphere that matches ground
      measurements of temperatures. Courtesy of NASA Marshall Space Flight
      Center.

      Global surface temperatures today are about 0.75 degrees Celsius
      warmer than at the beginning of the 20th century. Land regions have
      warmed the most, with the greatest warming in the winter and spring
      months over the northern hemisphere's continents.

      In the past few years, improvements have been made to both land-
      surface air temperature and sea-surface temperature coverage and
      daily data availability. One area of improvement relates to
      quantification of the effects of urbanization on the global
      temperature record and recognizing that the urban heat island effect
      is real. Another is the recovery and digitization of data from old
      oceanographic records, locked away in ship logs, that have filled in
      gaps in the past record.

      The past year has also seen increased understanding of the
      temperature records from balloon-borne radiosondes and estimates of
      upper-air temperatures from satellites that have provided true global
      coverage since 1979. Initial analyses indicated that temperatures in
      the lower atmosphere showed little or no warming. Climate change
      skeptics have used this result to raise questions about both the
      reliability of the surface record and the cause of the surface
      warming, as temperatures on the surface and in lower atmosphere
      should match. New datasets in the past five years, including some
      recent work published by Carl Mears and Frank Wentz, Benjamin Santer
      et al., and Steven Sherwood et al. in Science, help resolve this
      issue (see Geotimes,
      <http://www.geotimes.org/current/feature_climate.html#links>
      October 2005). Flaws have been discovered in the
      original satellite temperature record associated with orbital changes
      and satellite drift, and new analyses indicate that the lower
      atmosphere has been warming similarly to the surface since 1979. The
      surface and upper-air records of temperature change can now be
      reconciled, and the overall vertical pattern of observed temperature
      change is consistent with that simulated by today's climate models.

      The number of daily warm extremes has increased, while the number of
      cold extremes has decreased, especially at night.

      The warming described is also consistent with a body of other
      observations indicating a warming world. For example, the number of
      frost days in middle-latitude regions has decreased, principally due
      to an earlier last day of frost in spring. The number of daily warm
      extremes has increased, while the number of cold extremes has
      decreased, especially at night. Widespread increases in surface water
      vapor have been found since 1976, and the amount of total water vapor
      in the atmosphere has increased over the global oceans by 2 percent
      from 1988 to 2003, consistent in pattern and amount with changes in
      sea-surface temperatures and a fairly constant relative humidity.

      Ocean temperatures have warmed at depth as well, and global sea
      levels have risen 15 to 20 centimeters over the 20th century, with
      some evidence of an accelerating rate in the past decade (3.0
      centimeters). As the oceans warm, seawater expands and sea level
      rises, but nearly worldwide glacial melt also contributes to the
      increase. These changes provide fuel for tropical storms, such as
      Hurricane Katrina, and enhance associated heavy rains and flooding,
      likely contributing to the breaching of levees (see story, this
      issue). <http://www.geotimes.org/current/feature_climate.html#links>

      Snow cover has decreased in many northern hemisphere regions,
      particularly in spring. Sea-ice extents have decreased in the Arctic,
      particularly in the spring and summer seasons. In the Antarctic,
      patterns of warming and cooling are related to changes in global
      atmospheric circulation. The warming of the Antarctic Peninsula
      region since the early 1950s is one of the largest and the most
      consistent warming signals observed: Large reductions in sea ice and
      in the size of the Larsen Ice Shelf have occurred, including the
      collapse of the Larsen B Ice Shelf in 2002, which Eugene Domack and
      co-workers recently reported in Nature to be the largest to have
      occurred there in the last 10,000 years.

      Considerable progress has also been made in sorting out the role of
      changes in the sun, pollution (aerosols) and greenhouse gases, such
      as carbon dioxide. Aerosols, such as soot and sulfate particles (the
      milky white haze seen from airplanes), have short lifetimes (a week
      or so) as they are washed out of the atmosphere by rain, but their
      overall influence is to cool the climate and possibly change rainfall
      patterns. In contrast, greenhouse gases such as carbon dioxide,
      methane and nitrous oxide are not washed out. Many, such as carbon
      dioxide and nitrous oxide, have lifetimes of a century or longer.
      Hence they build up in the atmosphere over time, as observed. Carbon
      dioxide is now 32 percent higher than in preindustrial times, with
      half of the increase occurring since 1970, owing mainly to combustion
      of fossil fuels and deforestation. Greenhouse gas concentrations in
      the atmosphere are now higher than at any time in at least the last
      750,000 years.

      Climate model simulations have reliably shown that the global surface
      warming of recent decades is a response to the increased
      concentrations of greenhouse gases in the atmosphere. When the models
      are run without the human-made changes in atmospheric composition,
      they fail to capture the increase in global surface temperatures
      observed since the mid-1970s. But with anthropogenic forcings
      included, the models simulate the observed temperature record with
      impressive fidelity. These same model experiments also reveal that
      changes in solar luminosity account for much of the warming in the
      first half of the 20th century.

      Uncertainties arise from shortcomings in our understanding of climate
      processes, and how to best represent those processes in models. In
      recent years, climate models have improved, as they are run at higher
      resolutions, and representations of many processes (such as those
      involving cloudiness) have become more realistic. Today's best
      climate models are able to reproduce the climate of the past century,
      and simulations of the evolution of global surface temperatures over
      the past millennium are consistent with paleoclimate reconstructions.
      Hence they are useful tools for carrying out numerical climate
      experiments and making predictions.

      Climate change is with us; we cannot stop it, although we can slow it
      down. It behooves us therefore to track how and why the climate is
      changing. New data will provide the basis for more detailed
      predictions of what will happen over the next few decades, using new
      and improved climate models, together allowing us to plan for the
      future in an informed way.
      ----------------------------------------------------------------------

      Trenberth, an atmospheric scientist, is head of the Climate Analysis
      Section at the National Center for Atmospheric Research in Boulder,
      Colo. E-mail: trenbert@....

      Links:
      "Revisiting the satellite record," Geotimes, October 2005.
      <http://www.geotimes.org/oct05/NN_satellitetemps.html>

      "Global climate affects storms?" Geotimes, December 2005.
      <http://www.geotimes.org/current/highlights_climatestories.html>

      Further Reading:
      Barnett, T. P., D. W. Pierce, K. M. AchutaRao, P. J. Gleckler, B. D.
      Santer, J. M. Gregory, W. M., Washington, 2005: Penetration of Human-
      Induced Warming into the World's Oceans. Science, 309: 284-287
      Brohan, P. et al., 2005: Uncertainty estimates in regional and global
      observed temperature changes , J. Geophys. Res. (submitted).
      Emanuel, K., 2005: Increasing destructiveness of tropical cyclones
      over the past 30 years. Nature, 436, 686-688.
      Hansen, J., L. Nazarenko, R. Ruedy, M. Sato, J. Willis, A. Del Genio,
      D. Koch, A. Lacis, K. Lo, S. Menon,T. Novakov, J. Perlwitz, G.
      Russell, G. Schmidt, N. Tausnev, 2005: Earth's Energy Imbalance:
      Confirmation and Implications. Science, 308: 1431-1435
      Mears, C.A. and F.J. Wentz, 2005: The effect of diurnal correction on
      satellite-derived lower tropospheric temperature. Science, 309, doi:
      10.1126/science.1114772 (online).
      Peterson, T.C. and T.W. Owen, 2005: Urban heat island assessment:
      Metadata are important. J. Climate, 18, 2637-2646.
      Rayner, N.A., et al., 2005: Improved analyses of changes and
      uncertainties in marine temperature measured in situ since the mid-
      nineteenth century. J. Climate, Submitted.
      Santer, B.D., et al., 2005: Amplification of surface temperature
      trends and variability in the tropical atmosphere. Science, 309, doi:
      10.1126/science.1114867 (online).
      Sherwood, S., J. Lanzante, and C. Meyer, 2005: Radiosonde daytime
      biases and late 20th century warming. Science, 309, doi:
      10.1126/science.1115640 (online).
      Trenberth, K.E., J. Fasullo, and L. Smith, 2005: Trends and
      variability in column integrated atmospheric water vapor. Climate
      Dyn., 24, 741 758.
      Trenberth, K. E., 2005: Uncertainty in hurricanes and global warming.
      Science, 308, 1753-1754.

      Posted by Tim
      AustinTex
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