Scientists are more convinced that human activity is behind the
increase in global temperatures since the 1950s, which has boosted sea
levels and the odds of extreme storms, according to a leaked draft of an
upcoming U.N. report.
"It is extremely likely
that human influence on climate caused more than half of the observed
increase in global average surface temperature from 1951 to 2010,"
according to a summary of the draft obtained by CNN. "There is high
confidence that this has warmed the ocean, melted snow and ice, raised
global mean sea level and changed some climate extremes in the second
half of the 20th century."
Those conclusions come
from the upcoming report of the U.N. Intergovernmental Panel on Climate
Change, the fifth in a series of multiyear reports seen as a benchmark
on the subject. The panel's last report, in 2007, concluded that it was
90% certain that rising temperatures were due to human activity; the new
draft raises that figure to 95%.
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The panel's report is
slated for release in sections, starting in September, and could be
revised. But Marshall Shepherd, a research meteorologist at the
University of Georgia and the president of the American Meteorological
Society, said the report is expected "to strongly identify the
significant human impact on the climate system."
"There are certainly some
uncertainties that should be acknowledged, but the consensus is very
clear that humans are playing a significant role," said Shepherd, who
contributed to the 2007 report but was not involved in compiling the
upcoming document.
Increasing concentrations
of carbon dioxide and other emissions have driven up global average
temperatures by about 0.6 degrees C (1 degree F) since 1950, the report
states. That's likely to go up by between 1 and 3.7 degrees C (1.8 to
6.6 F) by 2100, the draft states.
Meanwhile, the rise of
sea levels, currently about 3 mm (1/8 inch) per year, is "very likely"
to speed up. Global average sea levels are expected to go up between 50
and 97 cm -- 20 inches to more than 3 feet -- by 2100, according to the
draft.
"Emissions at or above
current rates would induce changes in all components in the climate
system, some of which would very likely be unprecedented in hundreds to
thousands of years," it states. Those changes are likely to occur "in
all regions of the globe" and affect the water cycle, rising ocean
acidity and changes in the water cycle.
"Many of these changes would persist for many centuries," it added.
The effect has already
been seen in shrinking summer icepacks in the Arctic Ocean and warming
permafrost in the Northern Hemisphere, it states.
"It is very likely that
the Arctic sea ice cover will continue to shrink and thin and that
Northern Hemisphere snow cover will decrease during the 21st century as
global temperature rises," the draft states.
The science of global
warming is politically controversial but generally accepted as fact by
most researchers, who point to heat-trapping carbon emissions from the
burning of fossil fuels as the major cause. A May study of research papers
published between 1991 and 2011 found that more than 97% of those that
expressed an opinion on the cause of increasing temperatures supported
that consensus.
Skeptics point to the
fact that the rate of warming has slowed since 1998, a record warm year.
But two more years, 2005 and 2010, have topped that record -- and the
report notes that each of the last three decades have been warmer than
the last.
Meanwhile, the insurance industry and urban planners are treating sea-level rise as a real threat.
A study published over the weekend
in the scientific journal Nature Climate Change warned that the world's
largest coastal cities will face tens of billions in flood losses a
year even with improved defenses. The most vulnerable city on the list
was the Chinese city of Guangzhou, with Miami, New York, New Orleans and
Mumbai rounding out the top five.
New York and much of New Jersey are still rebuilding from 2012's catastrophic Superstorm Sandy, and a federal government report released Monday said reconstruction should take into account "the existing and future threats exacerbated by climate change."
"More than ever, it is
critical that when we build for the future, we do so in a way that makes
communities more resilient to emerging challenges such as rising sea
levels, extreme heat and more frequent and intense storms," Housing
Secretary Shaun Donovan wrote in the report's preface.
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