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Sun's Direct Role in Global Warming May Be Underestimated ...

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  • Mike Neuman
    The original title to the paper as published in GRLs is: Estimated Solar Contribution to the global surface warming using the ACRIM TSI satellite composite .
    Message 1 of 1 , Oct 7, 2005
      The original title to the paper as published in GRLs is: "Estimated
      Solar Contribution to the global surface warming using the ACRIM TSI
      satellite composite".

      The following concluding statement is found at the beginning of the
      article: "We estimate that the ACRIM upward trend (solar variation)
      might have minimally contributed ~10-30% of the global surface
      temperature warming over the period 1980-2002."

      Note the qualifying language: "might have minimimally contributed".

      ----------------------------------------------------------------------
      Sun's Direct Role in Global Warming May Be Underestimated, Duke
      Physicists Report

      Study does not discount the suspected contributions of 'greenhouse
      gases' in elevating surface temperatures

      Friday, September 30, 2005

      Durham, N.C. -- At least 10 to 30 percent of global warming measured
      during the past two decades may be due to increased solar output
      rather than factors such as increased heat-absorbing carbon dioxide
      gas released by various human activities, two Duke University
      physicists report.

      The physicists said that their findings indicate that climate models
      of global warming need to be corrected for the effects of changes in
      solar activity. However, they emphasized that their findings do not
      argue against the basic theory that significant global warming is
      occurring because of carbon dioxide and other "greenhouse" gases.
      Nicola Scafetta, an associate research scientistworking at Duke's
      physics department, and Bruce West, a Duke adjunct physics professor,
      published their findings online Sept. 28, 2005, in the research
      journal Geophysical Research Letters.

      West is also chief scientist in the mathematical and information
      sciences directorate of the Army Research Office in Research Triangle
      Park.

      Scafetta's and West's study follows a Columbia University
      researcher's report of previous errors in the interpretation of data
      on solar brightnesscollected by sun-observing satellites.
      The Duke physicists also introduce new statistical methods that they
      assert more accurately describe the atmosphere's delayed response to
      solar heating. In addition, these new methods filter out temperature-
      changing effects not tied to global warming, they write in their
      paper.

      According to Scafetta, records of sunspot activity suggest that solar
      output has been rising slightly for about 100 years. However, only
      measurements of what is known as total solar irradiance gathered by
      satellites orbiting since 1978 are considered scientifically
      reliable, he said.

      But observations over those years were flawed by the space shuttle
      Challenger disaster, which prevented the launching of a new solar
      output detecting satellite called ACRIM 2 to replace a previous one
      called ACRIM 1.

      That resulted in a two-year data gap that scientists had to rely on
      other satellites to try to bridge. "But those data were not as
      precise as those from ACRIM 1 and ACRIM 2," Scafetta said in an
      interview.

      Nevertheless, several research groups used the combined satellite
      data to conclude that that there was no increased heating from the
      Sun to contribute to the global surface warming observed between 1980
      and 2002, the authors wrote in their paper.

      Lacking a standardized, uninterrupted data stream measuring any
      rising solar influence, those groups thus surmised that all global
      temperature increases measured during those years had to be caused by
      solar heat-trapping "greenhouse" gases such as carbon dioxide,
      introduced into Earth's atmosphere by human activities, their paper
      added.

      But a 2003 study by a group headed by Columbia's Richard Willson,
      principal investigator of the ACRIM experiments, challenged the
      previous satellite interpretations of solar output. Willson and his
      colleagues concluded, rather that their analysis revealed a
      significant upward trend in average solar luminosity during the
      period.

      Using the Columbia findings as the starting point for their study,
      Scafetta and West then statistically analyzed how Earth's atmosphere
      would respond to slightly stronger solar heating. Importantly, they
      used an analytical method that could detect the subtle, complex
      relationships between solar output and terrestrial temperature
      patterns.

      The Duke analyses examined solar changes over a period twice as long -
      - 22 versus 11years -- as was previously covered by another group
      employinga different statistical approach.
      "The problem is that Earth's atmosphere is not in thermodynamic
      equilibrium with the sun," Scafetta said. "The longer the time period
      the stronger the effect will be on the atmosphere, because it takes
      time to adapt."

      Using a longer 22 year interval also allowed the Duke physicists to
      filter out shorter range effects that can influence surface
      temperatures but are not related to global warming, their paper said.
      Examples include volcanic eruptions, which can temporarily cool the
      climate, and ocean current changes such as el Nino that affect global
      weather patterns.
      Applying their analytical method to the solar output estimates by the
      Columbia group, Scafetta's and West's paper concludes that "the sun
      may have minimally contributed about 10 to 30 percent of the 1980-
      2002 global surface warming."

      This study does not discount that human-linked greenhouse gases
      contribute to global warming, they stressed. "Those gases would still
      give a contribution, but not so strong as was thought," Scafetta said.
      "We don't know what the Sun will do in the future," Scafetta
      added. "For now, if our analysis is correct, I think it is important
      to correct the climate models so that they include reliable
      sensitivity to solar activity.

      "Once that is done, then it will be possible to better understand
      what has happened during the past hundred years."

      Original Release:
      http://www.dukenews.duke.edu/2005/09/sunwarm.html
      ACRIM satellite:
      http://www.columbia.edu/cu/news/99/12/satellites2.html

      Title in GRL, Vol. 32, L18713, doi:10.1029/2005GL023849,2005:
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