September 27, 2013 / 8:47 AM / 4 years ago

UPDATE 3-Scientists say more certain mankind causes global warming

* 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 scientists said on
Friday they were more certain than ever before that humans are
the main culprits for climate change and predicted the impact
from greenhouse gas emissions could linger for centuries.
    The Intergovernmental Panel on Climate Change (IPCC) said in
a report that the current hiatus in warming, 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 that could swamp coasts and
low-lying islands as greenhouse gases built up in the
    Many world leaders called for stronger action to rein in
rising greenhouse gas emissions and limit a rise in temperatures
to within manageable limits after the report, which estimated
that humanity has burnt more than half the available carbon.
    The study, meant to guide governments in shifting towards
greener energies, said it was "extremely likely", 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 growth rather than fighting climate change, to work to
agree a planned U.N. accord in 2015 to combat global warming.
    "The heat is on. Now we must act," he said.
    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 after temperatures rose more
slowly over the last 15 years despite increasing greenhouse gas
emissions, especially in emerging nations led by China.
    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 predecessor
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 report said the trend of the past 15 years was skewed by
the fact that 1998, at the start of the period, was an extremely
warm year with an El Nino event in the Pacific that can disrupt
weather worldwide.
    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.
    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 the warming effect of carbon
    A doubling of carbon in the atmosphere would raise
temperatures by between 1.5 and 4.5 degrees Celsius (2.7 to
8.1F), below the 2-4.5 (3.6-8.1F) range in the 2007 report, it
said. The new range is identical to the ranges in IPCC studies
before 2007.
    The IPCC reiterated that a warming trend is "unequivocal",
and some effects would last far beyond the lifetimes of people
now alive, such as heat penetrating ever deeper into the oceans.
    "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," co-chair Thomas Stocker said.
    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, driven up by
melting ice and an expansion of water as it warms, 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.    
    "Scientists have confirmed what farmers in poor countries
around the world have been telling us for years, that changes to
their climate are destroying their livelihoods, ruining crops,
hitting incomes, food quality and often their family's health,"
said Winnie Byanyima, executive director of the charity Oxfam.
    About 15 protesters outside the conference hall dressed in
lab coats as doctors carried placards saying "Climate Change:
The debate is over."

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