The heat is on: how global warming could suddenly tip
over and ignite calamity
September 15, 2006
By Fiona Harvey
Scientists at Nasa, instead of staring into the skies,
have been using satellites to look down at the world
and track how it is changing. Within a year, the US
space agency disclosed this week, an area of sea ice
"the size of Texas" had been lost from the Arctic.
Data pieced together by Nasa showed that Arctic
perennial sea ice, which normally survives the summer
melting season, abruptly shrank by 14 per cent between
2004 and 2005. The report found: "Perennial ice can be
10 or more feet thick. It was replaced by new, seasonal
ice only one to seven feet thick that is more
vulnerable to summer melt."
The disappearance of Arctic ice, the retreat of
glaciers from the Himalayas to Peru, earlier springs
and hotter summers - all these effects have been
recorded by climate scientists in recent years. They
form the basis of Al Gore's polemic on climate change,
An Inconvenient Truth, in which the former US vice-
president describes huge cliffs of ice breaking apart,
glaciers dropping suddenly into the sea, and polar
bears found drowned because they cannot swim between
ice floes as they used to.
This, as everyone knows, is global warming. Even those
sceptical about whether the warming is caused by fossil
fuel combustion accept that world temperatures have
risen and look set to continue upward. Mr Gore's film,
which has been showing in the US since May - grossing
$23m (£12m, €18m) - and opens in the UK today, has
raised American awareness about climate change in the
face of the federal government's stance against the
Kyoto protocol, designed to curb it.
US state governments and businesses are beginning to
take action of their own to avert global warming by
reducing the greenhouse gas emissions under their
control. These measures, repeated across the globe, may
by some estimates allow the world to stabilise
emissions by the middle of the century.
But will that be soon enough? A growing body of
scientific opinion suggests the world may be about to
experience not a gradual rise in temperatures over
several decades but a wild careering into climate
That is because some of the changes triggered by
warming temperatures create a "feedback" effect of
their own. These feedbacks can cause the warming trend
to accelerate further or bring serious disruption to
regions of the world (see box).
In this view, the rising proportion of carbon dioxide
in the atmosphere, by creating feedbacks, is pushing
the earth's climate through a series of thresholds or
tipping points that threaten to bring cataclysmic
consequences. Those could include a much more rapid
melting of the Arctic ice and the Greenland ice sheet
than previously predicted, the accelerated melting of
permafrost, the cessation of the Indian monsoon, a
rapid dying back of forest in the Amazon and a halting
of the sea currents that help bring warm weather to
The most obvious of these magnifier effects is in the
Arctic, where the world's warming has been much more
pronounced than the average across the globe. Why? Sea
ice - because it is bright white - reflects back much
of the sun's rays, in effect cooling the planet, Mr
Gore's film explains. But melting ice leaves more of
the darker sea exposed, which then absorbs more heat,
which causes more ice to melt, thus exposing more sea -
a spiral of warming that quickly takes on a momentum of
The Nasa report appears to confirm this feedback loop.
There is more apparent confirmation in a study last
month in Science, journal of the American Association
for the Advancement of Science, that found the speed at
which the Greenland ice sheet was melting had risen
threefold in the past two years compared with the
Peter Smith, special professor in sustainable energy at
Nottingham University, told the British Association
science festival last week: "We could reach the tipping
point within 15 to 20 years from now, which would give
us just 10 years in which to determine the destiny of
our planet." Jay Gulledge, senior research fellow at
the Pew Centre on Global Climate Change, says
climatologists "have dramatically under-estimated how
responsive the climate is to warming".
The world's current attempts to cut emissions, such as
the Kyoto protocol and the Asia-Pacific Partnership on
Clean Development and Climate, a collaboration between
developed and developing countries, presume a slowdown
over decades of the rate of increase in the world's
output of greenhouse gases. But Myles Allen of Oxford
University, one of the leaders of a project that
predicted up to 11 degrees of warming, says: "The
danger zone is not something that we are going to reach
in the middle of this century. We are in it now."
"It is not too late to save the Arctic, but it requires
that we begin to slow CO2 emissions this decade," says
James Hansen, director of Nasa's Goddard Institute for
Talk of feedback effects and tipping points is still
controversial among scientists, however. Tim Lenton,
reader in earth systems analysis at the University of
East Anglia, is conducting a review of the science of
feedbacks and tipping points. He says: "There has been
quite a lot of hyperbole around this."
He says of fears that the Siberian permafrost is
melting: "A lot of people are saying there is a
positive feedback, which is true, but quite how strong
is the feedback? The impression is being given that
it's quite strong but actually it's quite weak."
Myron Ebell of the US Competitive Enterprise Institute,
a prominent sceptic on global warming, adds: "I don't
think [tipping points are] a scientific concept. It's a
popular cliché that is being used by the alarmists to
increase alarm. Mr Gore's slide show, movie and book
He continues: "The radiative forcing [temperature-
raising] effect of CO2 is not linear but logarithmic.
Each increment [of CO2] added will have less effect
than the previous increment. Another way of putting
this is that each doubling of CO2 results in the same
increase in forcing."
The idea of tipping points has helped galvanise
political opinion. Just as climate change itself
appears to be gathering momentum, so does the political
response. Robert Wyman of Latham and Watkins, a US law
firm, says Mr Gore's film and recent action to curb
emissions at state level have had a big effect on
To this he adds the effect of "new significant
scientific analyses" and "incremental but significant
additional political support in the US Senate", as well
as an increasing awareness of energy thanks to high
fuel prices. Hurricane Katrina, which devastated New
Orleans last year, also seems to have had an impact.
Action on emissions seems to be picking up. Later this
month governor Arnold Schwarzenegger will usher in the
mandatory curbs on emissions from energy-intensive
industries just approved by the California legislature.
Seven north-eastern states have agreed a separate
initiative to cap emissions from power stations in 2009
and reduce them by 10 per cent by 2019. Some think the
federal government may have to follow. Greg Gordon, an
analyst at Citigroup, says: "The political will to
regulate CO2 emissions in the US is gaining momentum.
Federal legislation is likely in the next few years."
Outside the US, concern over tipping points is also
intensifying pressure. In November, the signatories of
the United Nations' Framework Convention on Climate
Change - parent treaty to the Kyoto protocol - will
gather in the Kenyan capital Nairobi. They will be
assailed by non-governmental organisations urging
tougher action on emissions after the current
provisions of the protocol expire in 2012.
One of the main topics of informal discussion at the
meeting will be the fourth assessment report, due out
next year, of the Intergovernmental Panel on Climate
Change, the scientific study that underpins Kyoto. The
draft version of the report suggests that the notion of
tipping points and positive feedbacks will play a minor
role. It is likely to predict an average global warming
of 3 degrees Celsius by 2100.
Though some warn against overstating the feedback
effect and the near approach of tipping points, most
climate scientists accept the possibility that the
climate will change abruptly rather than warm
gradually. But this is not adequately taken into
account at the highest levels of politics. Mr Lenton,
describing this as a serious omission, says the climate
is subject to "highly non-linear change".
He elaborates: "The curve is not smooth, in other
words. But the typical economic approach has smooth
curves. This is a conceptual shift, from a smooth curve
to stepped rises, that if policy-makers could get hold
of could transform the way we think about this."