OSLO (Reuters) - A slowdown in the pace of
global warming so far this century is likely to be only a pause in a
longer-term trend of rising temperatures, the science academies of the
United States and Britain said on Thursday.
Since an exceptionally warm 1998, there has been "a short-term
slowdown in the warming of Earth's surface," Britain's Royal Society
and the U.S. National Academy of Sciences said in a report.
But, they said, that "does not invalidate our understanding of
long-term changes in global temperature arising from human-induced
changes in greenhouse gases."
The warming slowdown has emboldened those who question the evidence
about climate change and ask whether a shift in investments towards
renewable energies such as wind and solar power, advocated by many
experts, is really needed.
But the report said that scientists were "very confident" that the
planet would warm further this century, causing more extreme
heatwaves, droughts and rising seas.
A build-up of greenhouse gases from human activities, mainly the
burning of fossil fuels, is warming the atmosphere and the oceans,
raising sea levels and melting Arctic ice, the report said,
supporting the long-held view of a U.N. panel of climate scientists.
It projected that temperatures would rise by between 2.6 and 4.8
Celsius (4.7-8.6 F) by 2100 unless governments took strong action to
limit rising emissions of greenhouse gases, broadly in line with
Temperatures have gained about 0.8 C (1.4 F) since the 19th century.
Almost 200 nations have agreed to work out a deal by the end of 2015
to combat climate change. So far there has been little progress in
negotiations, partly because weak economic growth has sapped
Policy decisions were only possible if "based on the best possible
advice about the science of climate change," Paul Nurse, President
of the Royal Society, told a briefing.
The warming hiatus may be caused by shifts in the oceans that are
absorbing more heat from the atmosphere, the report said. Other
studies suggest that sun-dimming volcanic eruptions or a lower
output from the sun may contribute.
Brian Hoskins, of Imperial College London, said warming trends in
past decades had varied a lot despite rising greenhouse gas
emissions. "It's a staircase rather than a gentle trend upwards," he
Among signs of rising temperatures, the report said that record
heatwaves had hit Australia in 2013, the United States in 2012,
Russia in 2010 and Europe in 2003. There had been fewer cold snaps,
like in the United States this winter.
"It is now more certain than ever, based on many lines of evidence,
that humans are changing Earth's climate," it said.
Last year, the U.N.'s panel on climate science raised the
probability that human activities, rather than natural variations,
were the main cause of warming since the 1950s, to at least 95
percent from 90 in a previous assessment in 2007.