Royal Astronomical Society Gold Medal winner backs link between greenhouse gases and climate change (Forwarded)

Royal Astronomical Society
London, U.K.

Issued by RAS Press Officers:

Robert Massey
Tel: +44 (0)20 7734 4582
AND
Anita Heward
Tel: +44 (0)1483 420 904

NATIONAL ASTRONOMY MEETING PRESS ROOM (16 - 20 APRIL ONLY):
Tel: +44 (0)1772 892 613
+44 (0)1772 892 475
+44 (0)1772 892 477

RAS Web site:
http://www.ras.org.uk/

RAS National Astronomy Meeting web site:
http://nam2007.uclan.ac.uk

CONTACT:

Professor Nigel Weiss
Centre for Mathematical Sciences, University of Cambridge
Tel: +44 (0)1223 337 910

From 16 to 20 April, Professor Weiss can be contacted via the NAM press
office (see above).

PRESS INFORMATION NOTE: RAS PN 07/22 (NAM 18)

EMBARGOED FOR 00:01 BST, WEDNESDAY, 18 APRIL 2007

RAS GOLD MEDAL WINNER BACKS LINK BETWEEN GREENHOUSE GASES AND CLIMATE CHANGE

Professor Nigel Weiss, 2007 winner of the Royal Astronomical Society (RAS)
Gold medal, will rebut claims that a fall in solar activity could cancel out
the effects of man-made global warming. In a lecture on Wednesday 18 April
at the RAS-sponsored National Astronomy Meeting in Preston, Professor Weiss,
who is Emeritus Professor in Mathematical Astrophysics at the University of
Cambridge, will describe how solar activity was an important factor in past
climate change but that current global warming is very much driven by human
activity -- specifically the emission of greenhouse gases.

Solar magnetic activity manifests itself in sunspots, flares and coronal
mass ejections, which give rise to magnetic storms on earth. The incidence
of sunspots, which are the sites of strong magnetic fields, varies
cyclically with a period of about 11 years. This cyclic pattern is
occasionally interrupted by grand minima, like the Maunder Minimum in the
17th century, when scarcely any spots appeared. From variations in Carbon-14
(which is preserved in trees) and Beryllium-10 (which can be measured in
polar ice cores) we know that grand minima have recurred irregularly for at
least the last 50,000 years.

For the past 50 years, solar activity has in fact been abnormally high, but
such grand maxima do not last forever. The current boom will inevitably be
followed by a slump, though it is impossible to forecast quite when this
will happen, or how deep the ensuing grand minimum will be.

Although sunspots are themselves dark, they are accompanied by bright
faculae. Satellite observations show that the solar output of radiation
(irradiance) is actually greater at sunspot maximum than at sunspot minimum,
though the change of only 0.1% is slight, corresponding to a variation of
0.1 degrees Celsius in average global temperature. A grand minimum might
lead to a similar reduction in irradiance.

Of course, the effects of solar variability on the earth's climate, which is
a very complex system, could be amplified by other processes. For instance,
the Sun's ultra-violet emission doubles from sunspot minimum to maximum, and
ultra-violet radiation affects the ozone content of the stratosphere, which
is coupled to the troposphere below it and so influences the overall
climate. Again, it has been suggested that solar modulation of the flux of
galactic cosmic rays affects cloud formation, altering the amount of
radiation the Earth reflects back into space and affecting climate (though
this hypothesis is very shaky). There might also be a coupling between
variations in solar activity and natural oscillations in the atmosphere or
ocean.

The extent of any such climatic modulation can be estimated from the
long-term record of global temperatures. Until the beginning of the last
century, variations in solar activity, along with aerosol emission from
volcanoes, dominated climatic variability. There is persuasive evidence
that grand minima were indeed associated with colder periods and grand
maxima with warm periods. During the past millennium, there were several
such maxima and minima, with associated fluctuations of around 0.3 degrees
Celsius in global temperature. But these changes are significantly smaller
than the increase of almost one degree over the last hundred years so it
follows that solar activity is not a major contributor to current global
warming.

A minority of commentators have suggested that solar activity is a more
important cause than human, and that a fall in solar activity would lead to
cooling that could cancel out the effects of greenhouse gases.

While there have been reports that Professor Weiss backs this view, he
stressed that this was untrue and that the man-made causes of global warming
were of grave and far greater concern.

"Although solar activity has an effect on the climate, these changes are
small compared to those associated with global warming," he said. "Any
global cooling associated with a fall in solar activity would not
significantly affect the global warming caused by greenhouse gases."

"This is of course a controversial issue and there is a vocal lobby arguing
against the link between anthropogenic gas emissions and climatic change.
However I share the view of the majority of the scientific community that
the evidence for such a link and thus the occurrence of man-made global
warming is significant and a matter of grave concern."

NOTES FOR EDITORS

The 2007 RAS National Astronomy Meeting is hosted by the University of
Central Lancashire. It is sponsored by the Royal Astronomical Society and
the UK Science and Technology Facilities Council.

This year the NAM is being held together with the UK Solar Physics (UKSP)
and Magnetosphere, Ionosphere and Solar-Terrestrial (MIST) spring meetings.
2007 is International Heliophysical Year.

The RAS, founded in 1820, encourages and promotes the study of astronomy,
solar-system science, geophysics and closely related branches of science.
The Society represents UK astronomy nationally and internationally. Its more
than 3000 members (Fellows), a third based overseas, include scientific
researchers in universities, observatories and laboratories as well as
historians of astronomy and others.

The RAS Gold Medal is the Society's highest honour and two are awarded
annually. One medal is for achievement in geophysics, solar physics,
solar-terrestrial physics or planetary sciences (the 'G' award) and the
other is for achievement in astronomy, cosmology, astroparticle physics and
cosmochemistry (the 'A' award).