Global warming Armageddon?
Calculations from Canadian and US scientists show runaway greenhouse
effect is a realistic possibility
A runaway greenhouse Armageddon in which the oceans boil dry could
theoretically happen on Earth, researchers claim. The good news is that
human activity on its own will probably not be enough to trigger such an
end-of-the-world scenario in the near future.
Previously it was thought more energy from the sun would be needed
for global warming on Earth truly to spin out of control. But new
calculations from Canadian and US scientists show that catastrophic
warming can occur more easily than had been assumed.
 For a planet receiving the same amount of solar radiation as the
Earth, a runaway greenhouse effect is a realistic possibility. The team,
led by Colin Goldblatt from the University of Victoria in Canada, wrote
in Nature Geoscience: "The runaway greenhouse may be much easier to
initiate than previously thought.
"A renewed modelling effort is needed, addressing both Earth and
planetary science applications."
To see what might happen to the Earth if it was ever caught in the
grip of runaway global warming, it is only necessary to look next door.
Venus, our closest neighbour in space, is believed to have experienced a
runaway greenhouse effect in the past.
Shrouded in a dense carbon dioxide atmosphere, it has an average
surface temperature of around 460C - hot enough to melt lead.
The new study used a simplified model which did not take into account
the effect of clouds. But it still suggests that under certain
atmospheric conditions a stable Earth could switch to a runaway
greenhouse state.
Looking back in the Earth's history reveals past episodes of global
warming, but none involving a runaway greenhouse effect. There is no
clue to the size of any "safety margin", said the scientists.
A carbon dioxide greenhouse effect caused the "hothouse" climate of
the Eocene period 55 million years ago, when the Earth underwent more
warming than at any previous time in its history. Average global
temperature rose by up to 4C, and palm trees grew in the Arctic.
Eocene atmospheric carbon dioxide levels and temperature were both
higher than what is expected in the foreseeable future from man-made
greenhouse gas emissions, without triggering a runaway effect.
"This implies that an anthropogenic (human-caused) runaway greenhouse
is unlikely," the scientists wrote.
- PA
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