* Some 'tipping points' closer to being reached
* Loss of Siberian permafrost worrying, scientists say
By Nina Chestney
LONDON, March 26 The world is close to reaching
tipping points that will make it irreversibly hotter, making
this decade critical in efforts to contain global warming,
scientists warned on Monday.
Scientific estimates differ but the world's temperature
looks set to rise by six degrees Celsius by 2100 if greenhouse
gas emissions are allowed to rise uncontrollably.
As emissions grow, scientists say the world is close to
reaching thresholds beyond which the effects on the global
climate will be irreversible, such as the melting of polar ice
sheets and loss of rainforests.
"This is the critical decade. If we don't get the curves
turned around this decade we will cross those lines," said Will
Steffen, executive director of the Australian National
University's climate change institute, speaking at a conference
Despite this sense of urgency, a new global climate treaty
forcing the world's biggest polluters, such as the United States
and China, to curb emissions will only be agreed on by 2015 - to
enter into force in 2020.
" We are on the cusp of some big changes," said Steffen. "We
can ... cap temperature rise at two degrees, or cross the
threshold beyond which the system shifts to a much hotter
For ice sheets - huge refrigerators that slow down the
warming of the planet - the tipping point has probably already
been passed, Steffen said. The West Antarctic ice sheet has
shrunk over the last decade and the Greenland ice sheet has lost
around 200 cubic km (48 cubic miles) a year since the 1990s.
Most climate estimates agree the Amazon rainforest will get
drier as the planet warms. Mass tree deaths caused by drought
have raised fears it is on the verge of a tipping point, when it
will stop absorbing emissions and add to them instead.
Around 1.6 billion tonnes of carbon were lost in 2005 from
the rainforest and 2.2 billion tonnes in 2010, which has undone
about 10 years of carbon sink activity, Steffen said.
One of the most worrying and unknown thresholds is the
Siberian permafrost, which stores frozen carbon in the soil away
from the atmosphere.
"There is about 1,600 billion tonnes of carbon there - about
twice the amount in the atmosphere today - and the northern high
latitudes are experiencing the most severe temperature change of
any part of the planet," he said.
In a worst case scenario, 30 to 63 billion tonnes of carbon
a year could be released by 2040, rising to 232 to 380 billion
tonnes by 2100. This compares to around 10 billion tonnes of CO2
released by fossil fuel use each year.
Increased CO2 in the atmosphere has also turned oceans more
acidic as they absorb it. In the past 200 years, ocean
acidification has happened at a speed not seen for around 60
million years, said Carol Turley at Plymouth Marine Laboratory.
This threatens coral reef development and could lead to the
extinction of some species within decades, as well as to an
increase in the number of predators.
As leading scientists, policy-makers and environment groups
gathered at the "Planet Under Pressure" conference in London,
opinions differed on what action to take this decade.
London School of Economics professor Anthony Giddens favours
focusing on the fossil fuel industry, seeing as renewables only
make up 1 percent of the global energy mix.
"We have enormous inertia within the world economy and
should make much more effort to close down coal-fired power
stations," he said.
Oil giant Royal Dutch Shell favours working on
technologies leading to negative emissions in the long run, like
carbon capture on biomass and in land use, said Jeremy Bentham,
the firm's vice president of global business environment.
The conference runs through Thursday.