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 University of Reading
and the Met Office, 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 Intergovernmental Panel on Climate Change’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 0.13 C.
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.
Professor 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.
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 behavior is a
reasonable guide for future solar activity changes.”
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.”
