New research has
found that solar output is likely to reduce over the next 90 years
but that will not substantially delay expected increases in global
temperatures caused by greenhouse gases.
Carried out by the Met Office and the University of Reading, the
study establishes the most likely changes in the Sun’s activity
and looks at how this could affect near-surface temperatures on Earth.
It found that the most likely outcome was that the Sun’s output
would decrease up to 2100, but this would only cause a reduction
in global temperatures of 0.08 °C. This compares to an expected
warming of about 2.5 °C over the same period due to greenhouse
gases (according to the IPCC’s B2 scenario for greenhouse gas
emissions that does not involve efforts to mitigate emissions).
Gareth Jones, a climate change detection scientist with the Met
Office, said: “This research shows that the most likely change in
the Sun’s output will not have a big impact on global temperatures
or do much to slow the warming we expect from greenhouse gases.
“It’s important to note this study is based on a single climate
model, rather than multiple models which would capture more of the
uncertainties in the climate system.”
The study also showed that if solar output reduced below that
seen in the Maunder Minimum – a period between 1645 and 1715 when
solar activity was at its lowest observed level – the global
temperature reduction would be 0.13C.
Peter Stott, who also worked on the research for the Met Office,
said: “Our findings suggest that a reduction of solar activity to
levels not seen in hundreds of years would be insufficient to
offset the dominant influence of greenhouse gases on global
temperatures in the 21st century.”
During the 20th century solar activity increased to a ‘grand
maximum’ and recent studies have suggested this level of activity
is at or nearing its end.
Mike Lockwood, an expert in solar studies at the University of
Reading, used this as a starting point for looking at the most
probable changes in the Sun’s activity over the 21st century.
Met Office scientists then placed the projections into one
climate model to see how they may impact temperatures.
Professor Lockwood said: "The 11-year solar cycle of
waxing and waning sunspot numbers is perhaps the best known way
the Sun changes, but longer term changes in its brightness are
more important for possible influences on climate.
“The most likely scenario is that we’ll see an overall reduction
of the Sun’s activity compared to the 20th century, such that
solar outputs drop to the values of the Dalton Minimum (around
1820). The probability of activity dropping as low as the Maunder
Minimum – or indeed returning to the high activity of the 20th
century – is about 8%. The findings rely on the assumption that
the Sun's past behaviour is a reasonable guide for future
solar activity changes.”
ENDS
Notes to Editors
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email r.cheeseman@reading.ac.uk
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