91av

IT SEEMS like a great idea: slow global warming by pumping carbon dioxide to
the bottom of the ocean, where it will remain locked up for centuries. But a new
model of the process and an experiment to test the idea are stirring up debate
about using our oceans as a dumping ground for greenhouse gases.

Helge Drange and his colleagues from the Nansen Environmental and Remote
Sensing Centre in Bergen, Norway, used computer models to show that CO₂
dumped at a depth of 800 metres in the Norwegian Sea would dissolve before it
bubbles to the surface. The heavier, gas-rich water would then sink to the
bottom, flow into the Atlantic Ocean and not rise to the surface for
centuries.

The idea is to extract CO₂ from waste gases, compress it to liquefy
it, and spray it into the deep water as small droplets that can easily dissolve.
鈥淚t鈥檚 fairly simple,鈥� says Drange. The estimated cost of disposing of CO₂
in this way would be about $39 per tonne, compared with a tax of
$32 per tonne currently paid by offshore rigs in Norwegian waters for
releasing CO₂ into the air.

While the researchers acknowledge that further studies are needed,
they think the plan could help to put a brake on global warming. But
environmentalists argue that polluting the ocean to save the air will only
create new problems and that the long-term effects are unknown. Some worry that
the acidity of the CO₂-rich water will kill wildlife or dissolve parts
of the seabed, and that climate change may alter ocean circulation, bringing the
CO₂ back to the surface sooner than we now expect.

An international team hopes to answer some of these questions by pumping a
small amount of CO₂ onto the seabed off Kona, Hawaii. But the project
faces serious opposition from the public and has been scaled down several times already
(91av, 3 March, p 7).
Stephen Masutani of the
University of Hawaii in Honolulu expects it will be delayed until next year.
鈥淧eople are scared because it鈥檚 an unknown,鈥� he says.

The Hawaiian project currently proposes to dump less than 40 tonnes of CO
₂ into the water over 10 days. On that scale, few people think the
experiment will cause significant damage. But Paul Johnston of the University of
Exeter, who works for Greenpeace, says that pursuing such projects may give
people an excuse not to reduce their emissions. 鈥淚t鈥檚 a totally irresponsible
way to convince people that there鈥檚 a get-out-of-jail-free card. There
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Johnston doubts that any amount of research will ever prove the strategy
safe. And, he estimates, the energy used to get the CO₂ liquefied and
down to the sea floor could create about 40 per cent as much gas again. 鈥淵ou鈥檙e
going to make the problem worse in the long term,鈥� he says.

Drange admits the strategy faces problems. But, he says, 鈥淲e
know the consequences of global warming. One should at least try to assess the
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