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 Eruptions of at least 17 volcanoes since 2000, including Nabro in
Eritrea, Kasatochi in Alaska and Merapi in Indonesia, ejected sulfur
whose sun-blocking effect had been largely ignored until now by
climate scientists, it said.
The pace of rising world surface temperatures has slowed since an
exceptionally warm 1998, heartening those who doubt that an urgent,
trillion-dollar shift to renewable energies from fossil fuels is
needed to counter global warming.
Explaining the hiatus could bolster support for a U.N. climate deal,
due to be agreed by almost 200 governments at a summit in Paris in
late 2015 to avert ever more floods, droughts, heat waves and rising
sea levels.
"This is a complex detective story," said Benjamin Santer of the
Lawrence Livermore National Laboratory in California, lead author of
the study in the journal Nature Geoscience that gives the most
detailed account yet of the cooling impact of volcanoes.
"Volcanoes are part of the answer but there's no factor that is
solely responsible for the hiatus," he told Reuters of the study by
a team of U.S. and Canadian experts.
Volcanoes are a wild card for climate change — they cannot be
predicted and big eruptions, most recently of Mount Pinatubo in the
Philippines in 1991, can dim global sunshine for years.
Santer said other factors such as a decline in the sun's output,
linked to a natural cycle of sunspots, or rising Chinese emissions
of sun-blocking pollution could also help explain the recent
slowdown in warming.
The study suggested that volcanoes accounted for up to 15 percent of
the difference between predicted and observed warming this century.
All things being equal, temperatures should rise because greenhouse
gas emissions have hit repeated highs.
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TEMPORARY RESPITE
"Volcanoes give us only a temporary respite from the relentless
warming pressure of continued increases in carbon dioxide," said
Piers Forster, Professor of Climate Change at the University of
Leeds.
A study by the U.N. Intergovernmental Panel on Climate Change last
year suggested that natural variations in the climate, such as an
extra uptake of heat by the oceans, could help explain the warming
slowdown at the planet's surface.
The IPCC projected a resumption of warming in coming years and said
that "substantial and sustained" cuts in greenhouse gas emissions
were needed to counter climate change.
It also raised the probability that human activities were the main
cause of warming since 1950 to at least 95 percent from 90 in 2007.
Despite the hiatus, temperatures have continued to rise — 13 of the
14 warmest years on record have been this century, according to the
World Meteorological Organisation.
For the study, click on:
http://dx.doi.org/10.1038/ngeo2098
(Reporting by Alister Doyle; editing by Alistair Lyon)
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