UPDATE 5-Scientists more convinced mankind is main cause of warming

Fri Sep 27, 2013 1:15pm EDT
 
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* IPCC raises probability warming mostly manmade to 95 pct
    * Says slowing in warming trend linked to natural variations


    By Alister Doyle and Simon Johnson
    STOCKHOLM, Sept 27 (Reuters) - Leading climate scientists
said on Friday they were more convinced than ever that humans
are the main culprits for global warming, and predicted the
impact from greenhouse gas emissions could linger for centuries.
    The Intergovernmental Panel on Climate Change (IPCC) said in
a report that a hiatus in warming this century, when
temperatures have risen more slowly despite growing emissions,
was a natural variation that would not last.
    It said the Earth was set for more heatwaves, floods,
droughts and rising sea levels from melting ice sheets that
could swamp coasts and low-lying islands as greenhouse gases
built up in the atmosphere. 
    The study, meant to guide governments in shifting towards
greener energies, said it was "extremely likely", with a
probability of at least 95 percent, that human activities were
the dominant cause of warming since the mid-20th century.
    That was an increase from "very likely", or 90 percent, in
the last report in 2007 and "likely", 66 percent, in 2001.
    U.N. Secretary-General Ban Ki-moon said the study was a call
for governments, many of which have been focused on spurring
weak economies rather than fighting climate change, to work to
reach a planned U.N. accord in 2015 to combat global warming.
    "The heat is on. Now we must act," he said of the report
agreed in Stockholm after a week of talks between scientists and
delegates from more than 110 nations.
    U.S. Secretary of State John Kerry said the report was a
wake-up call. "Those who deny the science or choose excuses over
action are playing with fire," he said, referring to sceptics
who question the need for urgent action.
    They have become emboldened by the fact that temperatures
rose more slowly over the last 15 years despite increasing
greenhouse gas emissions, especially in emerging nations led by
China. Almost all climate models failed to predict the slowing.
 
     
    "LOOKING FOR THE CURE"
    European Climate Commissioner Connie Hedegaard said it was
time to treat the Earth's health. "If your doctor was 95 percent
sure you had a serious disease, you would immediately start
looking for the cure," she said.
    Compiled from the work of hundreds of scientists, the report
faces extra scrutiny this year after its 2007 edition included
an error that exaggerated the rate of melting of Himalayan
glaciers. An outside review later found that the mistake did not
affect its main conclusions.
    The IPCC said some effects of warming would last far beyond
current lifetimes.
    Sea levels could rise by 3 metres (9 feet, 10 inches) under
some scenarios by 2300 as ice melted and heat made water in the
deep oceans expand, it said. About 15 to 40 percent of emitted
carbon dioxide would stay in the atmosphere for more than 1,000
years.
    "As a result of our past, present and expected future
emissions of carbon dioxide, we are committed to climate change
and effects will persist for many centuries even if emissions of
carbon dioxide stop," said Thomas Stocker, co-chair of the
talks.
    The IPCC said humanity had emitted about 530 billion tonnes
of carbon, more than half the 1 trillion tonne budget it
estimated as a maximum to keep warming to manageable limits.
Annual emissions are now almost 10 billion tonnes and rising.
    Explaining a recent slower pace of warming, the report said
the past 15-year period was skewed by the fact that 1998 was an
extremely warm year with an El Nino event - a warming of the
ocean surface - in the Pacific.
    It said warming had slowed "in roughly equal measure"
because of random variations in the climate and the impact of
factors such as volcanic eruptions, when ash dims sunshine, and
a cyclical decline in the sun's output.
    Rajendra Pachauri, chair of the IPCC, told Reuters the
reduction in warming would have to last far longer - "three or
four decades" - to be a sign of a new trend.
    And the report predicted that the reduction in warming would
not last, saying temperatures from 2016-35 were likely to be
0.3-0.7 degree Celsius (0.5 to 1.3 Fahrenheit) warmer than in
1986-2005.
    Still, the report said the climate was slightly less
sensitive than estimated to warming from carbon dioxide.
    A doubling of carbon in the atmosphere would raise
temperatures by between 1.5 and 4.5 degrees Celsius (2.7 to
8.1F), it said, below the 2-4.5 (3.6-8.1F) range in the 2007
report. The new range is identical to the ranges in IPCC studies
before 2007.
    The report said temperatures were likely to rise by
between 0.3 and 4.8 degrees Celsius (0.5 to 8.6 Fahrenheit) by
the late 21st century. The low end of the range would only be
achieved if governments sharply cut greenhouse gas emissions.
    And it said world sea levels could rise by between 26 and 82
cm (10 to 32 inches) by the late 21st century, in a threat
to coastal cities from Shanghai to San Francisco.
    That range is above the 18-59 cm estimated in 2007, which
did not take full account of Antarctica and Greenland. 
    Bjorn Lomborg, author of "The Skeptical Environmentalist"
said "the IPCC's moderate projections clearly contradict
alarmist rhetoric" of higher temperature and sea level rises by
some activists.