On a scale of scientific importance, Dr Henrik Svensmark and Dr Eigil
Friis- Christensen's research on cosmic rays and cloud formation may one day
rank as a world leader.
Yet its origins were obscure and its initial impact negligible. Pain-
stakingly assembled from weather satellite data and other astonomical
observations, the two Danish meterorologists' report was buried in a few
pages of the Journal of Atmospheric and Solar-Terrestrial Physics last year.
It made little impact at the time, but slowly the paper has acquired a cult
status among physicists. And it may yet prove to be a scientific milestone.
What Svensmark and Friis-Christensen discovered was simple: over the past
15 years they saw an exact correlation between levels of cosmic rays hitting
Earth and the proportion of the world's skies obscured by clouds. The
effect may not seem profound: a typical 20% drop in cosmic ray levels
reduces cloud cover from 68 to 65%. Nevertheless the impact for our planet
is considerable.
"Clouds have a profound effect on Earth's radiation budget," says Dr
Jasper Kirkby of CERN, the international centre for particle physics
research at Geneva. "The more cloud cover there is, the cooler will be the
climate. Fewer clouds, and the planet will warm up."
And our planet is warming up. Over the last 100 years global temperatures
have risen by about .5=B0 Celsius. It had been assumed that this was the
result of a steady rise in industrial activity - more and more factories,
cars and homes spewing out carbon dioxide and other greenhouse gases,
trapping the sun's heat and warming the atmosphere.
But there are inconsistencies in this simple picture. For example, global
temperatures fell slightly between 1945 and 1970, a fact that cannot be
explained by the steadily rising emissions over that period.
Some scientists have continued to argue that other factors must be
involved. The importance of the work by Svensmark and Friis-Christensen is
that they have provided these doubters with a convincing alternative
candiate - cosmic rays.
Our planet is bathed in cosmic rays, a heavenly rain of sub-atomic
particles that pour down upon us from deepest space. Researchers believe
that the particles were probably spewed into the cosmos by exploding=
supernovae.
Cosmic rays trigger a cascade of other particles when they strike atoms
in the upper atmosphere, creating a background of natural radiation on
Earth. This radiation would not be expected to fluctuate - were it not for
the sun. The sun pours out gusts of its own sub-atomic particles. We call
this the solar wind. It protects Earth from cosmic rays, sweeping them away
from our planet.
In other words, when the solar wind is intense, fewer cosmic rays hit
Earth, cloud cover is reduced and temperatures rise. And there is
compelling evidence to support this idea because there is an easy way to
tell when the solar wind is strong. Just count sunspots. The more there are,
the stronger the solar wind.
Claims of a link between sunspots and the weather are not new, of course.
The great astonomer William Herschel noticed that the price of wheat in 18th
century England was lower when there were many sunspots and the weather was
warm. In the second half of the 17th century, when sunspots almost
disappeared, the Earth went through a miniature ice age.
Crucially scientists have discovered that sunspot activity has been
changing radically over the past century. The solar winds have become
stronger and stronger.
The only link that has yet to be established is the mechanism by which
cosmic rays influence cloud formation. This is why Kirby and Dr Frank
Close, another British physicist, have proposed building a cloud detector at
CERN.
This machine would recreate Earth's atmosphere. A chamer containing the
gases, water vapour and aerosol particles found in our atmosphere would be
battered with sub-atomic particles from one of CERN's accelerators to reveal
the exact mechanism that links sunspot activity with atmospheric heating.
In this way, the expertise of the world's leading particle physicists
would be brought to bear on a critical environmental issue.
If they succeed in establishing a link, a major environmental shibboleth
- that mankind is responsible for the rise in global temperatures - will be
destroyed, with profound political implications. Fear that continued
industrial development urgently sought by the developing world, might have
devastating consequences could then be discounted, although other valid
concerns about acid rain and ozone depletion would remain.