Scientists more convinced mankind is main cause of warming

Reuters

* 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.

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