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COSMIC RAYS, CLOUDS, AND CLIMATE

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  • Mike Doran
    From Scienceweek earlier this week and excerpt from Science, 2002, 298:1732 3. COSMIC RAYS, CLOUDS, AND CLIMATE The following points are made by K. S. Carslaw
    Message 1 of 1 , Jul 7, 2003
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      From Scienceweek earlier this week and excerpt from Science, 2002,
      298:1732

      3. COSMIC RAYS, CLOUDS, AND CLIMATE

      The following points are made by K. S. Carslaw et al (Science 2002
      298:1732):

      1) The correlation between cosmic rays and Earth's cloud cover over
      a solar cycle, first reported by Svensmark and Friis- Christensen in
      1997, was hailed by some as the missing piece in the puzzle of
      understanding how the Sun could influence climate change. The
      intensity of cosmic rays varies globally by about 15% over a solar
      cycle because of changes in the strength of the solar wind, which
      carries a weak magnetic field into the heliosphere, partially
      shielding Earth from low-energy galactic charged particles. Although
      long suspected of having some influence on atmospheric processes,
      the correlation between cosmic rays and global cloudiness was to
      some researchers the clearest indication that such a link might
      exist.

      2) Changes in cloud cover are important because clouds exert a
      strong control over Earth's radiative balance. Since the original
      observation, improved satellite data have become available and the
      cosmic ray-cloud effect seems to be present in low-altitude clouds.
      Because low clouds exert a large net cooling effect on the climate,
      this determines the sign of the possible cosmic ray- cloud effect:
      More cosmic rays are associated with more low clouds and lower
      temperatures. The observed variation of low clouds by about 1.7%
      absolute corresponds to a change in Earth's radiation budget of
      about 1 Wm^(-2) between solar maximum and minimum. This change in
      energy input to the lower atmosphere is highly significant when
      compared, for example, with the estimated radiative forcing of 1.4
      Wm^(-2) from anthropogenic CO2 emissions.

      3) In summary: It has been proposed that Earth's climate could be
      affected by changes in cloudiness caused by variations in the
      intensity of galactic cosmic rays in the atmosphere. This proposal
      stems from an observed correlation between cosmic ray intensity and
      Earth's average cloud cover over the course of one solar cycle. Some
      scientists question the reliability of the observations, whereas
      others, who accept them as reliable, suggest that the correlation
      may be caused by other physical phenomena with decadal periods or by
      a response to volcanic activity or El Nino. Nevertheless, the
      observation has raised the intriguing possibility that a cosmic ray-
      cloud interaction may help explain how a relatively small change in
      solar output can produce much larger changes in Earth's climate.
      Physical mechanisms have been proposed to explain how cosmic rays
      could affect clouds, but they need to be investigated further if the
      observation is to become more than just another correlation among
      geophysical variables.

      Related Material:

      ON COSMIC RAYS

      Radio, X-ray and gamma-ray astronomy have resulted in many
      discoveries which can only be interpreted in terms of the presence
      of large fluxes of relativistic particles in galaxies. In parallel
      with these developments, cosmic ray studies opened up new areas of
      astrophysical importance through direct observation of high energy
      particles at the top of the atmosphere and in the environment of the
      Earth from satellites and, for the very highest energy cosmic rays,
      from the surface of the Earth by the large air-shower arrays.

      Cosmic radiation (what we would now call cosmic rays) was discovered
      as long ago as 1912 by Victor Hess (1883-1964), but the
      astrophysical understanding of the origin and propagation of these
      particles had to await the 1960s when cosmic ray particle detectors
      were flown in satellites. These observations established many
      crucial facts about the particles detected in the cosmic radiation.
      First of all, the energy spectra of the particles are almost exactly
      the same as the typical spectrum of high-energy articles inferred to
      be present in both Galactic and extragalactic nonthermal radio
      sources. Observations indicate that the cosmic ray particles
      observed at the top of the atmosphere are only part of a population
      of high-energy particles pervading the whole Galaxy.

      Subsequent satellite observatories have determined the chemical
      composition and detailed energy spectra of cosmic ray nuclei.
      Remarkably, the chemical composition of the cosmic rays is similar
      to the abundances of the elements in the Sun, although there are
      some variations in the abundances at the higher energies. These
      observations provide evidence on the chemical composition of the
      cosmic rays as they left their sources and also about the
      modifications which could have taken place during propagation from
      their sources to the Earth. These observations are very important
      for high energy astrophysics because they are the only particles
      which we can detect which have traversed a considerable distance
      through the interstellar medium and which were accelerated in events
      such as supernovae and possibly pulsars in the relatively recent
      past, probably within the last 10^(7) years.

      At the very highest energies, cosmic rays are detected by large air-
      shower arrays on the surface of the Earth. The arrival rate of the
      most energetic particles is very low indeed, but particles with
      energies up to about 10^(20) eV have been detected. One important
      puzzle is the origin of these very high energy particles. Their
      arrival directions seem to be reasonably isotropic and, at these
      very high energies, these should not be significantly influenced by
      the magnetic field in our own Galaxy.

      Adapted from: Paul Davies (Ed.): The New Physics. Cambridge
      University Press 1989.

      ScienceWeek http://www.scienceweek.com

      Comment:

      What ISN'T discussed here is how the biosphere MODULATES this
      chaotic input--and the biosphere's ability to modulate its chemistry
      and temperature by EMFs on MUCH faster timescales than w/ CO2 as a
      green house gas. The electrical feedbacks are largely instantanious.
      This gets to the major criticisms of Gaia discussed in the 1970s and
      1980s when Lovelock wrote many of his ideas and repeated those of
      many others.

      NONE of the climatologists who claim to be "skeptics" have EMF and
      bio backgrounds. NONE of them.
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