Scientists more convinced mankind is main cause of warming

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
skeptics who question the need for urgent
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.
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
The IPCC said some effects of warming
would last far beyond current lifetimes.
Sea levels could rise by 3 meters (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 tons of carbon, more than half the
1 trillion ton budget it estimated as a
maximum to keep warming to manageable
limits. Annual emissions are now almost 10
billion tons 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
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.