Saturday, May 9, 2009

scientists must beware of “tinkering with a system you do not fully understand”

TO BE NOTED: From the FT:

Changing the planet might help preserve it

By Fiona Harvey, Environment Correspondent

Published: May 8 2009 17:28 | Last updated: May 8 2009 17:28

A giant mirror drifts slowly through space between the Earth’s surface and the sun, intercepting the rays of sunlight before they reach the Earth, and deflecting them safely away.

Eco engineeringThe mirror, made up of millions of silicon chips, is situated at a point in space where the sun’s gravity and the Earth’s cancel each other. This vast structure, assembled painstakingly for years by spacecraft, drifts naturally away from its starting point over time, but complex on-board systems nudge it gradually back to resume its vital role in keeping us safe.

This space mirror is – so far – science fiction. Such a structure would cost hundreds of billions of dollars, even if it were technically feasible. But soon many scientists say we may need to start building space mirrors, creating artificial clouds or altering the chemistry of the sea to prevent the worst effects of global warming.

Climate change is occurring faster than predicted, and the risks are growing day by day. Altering the Earth’s systems in order to help cool the planet may soon be the only option, many scientists believe, as our runaway appetite for fossil fuels overtakes our good intentions on emissions.

“The chances of reducing emissions fast enough now are very low,” said Stephen Salter, professor of engineering design at Edinburgh University. “This is a jolly strong reason to look at alternatives. It’s an insurance policy.”

An ocean of opportunity

Many proposals to save the planet through geo-engineering are immensely expensive and futuristic, writes Clive Cookson.

One of the most straightforward ideas, already tested on a small scale, is to stimulate the growth of plankton – microscopic algae and plants – in the oceans, by increasing the supply of nutrients.

A dozen trials so far have examined the effects of ocean iron fertilisation. The latest is taking place this spring: the Indian-German LohaFex experiment. The research vessel Polarstern, with 48 scientists on board, has distributed six tonnes of dissolved iron over 300 sq km of the Southern Ocean.

Results so far show that iron fertilisation does stimulate spectacular algal growth in the upper waters. What is not yet clear is whether this results in the long-term sequestration of CO2 – which would require a significant proportion of the algae to sink into the ocean depths after they die.

Several companies, such as Climos of the US, hope to commercialise ocean iron fertilisation, funding the activity by claiming carbon credits from emissions trading schemes. At present there is an international moratorium on large-scale commercial ocean fertilisation, in response to concerns about its impact on local ecosystems, but scientific trials such as LohaFex are permitted.

Although the focus so far has been on iron fertilisation, on the grounds that shortage of iron nutrients is the factor limiting algal growth in the open oceans, it would also be possible to add phosphorus and nitrogen fertilisers.

A study at the University of East Anglia, published in January, came to the surprising conclusion that adding phosphorus compounds (phosphates) to the oceans could have more long-term potential for carbon sequestration than adding iron or nitrogen. Even if we do not deliberately fertilise the ocean with phosphorus, human activities – mainly run-off from agricultural activities – are already increasing the amount of carbon locked up in the oceans.

A final possibility is to add crushed carbonate rocks (limestone) to the oceans. This would have the dual benefit of increasing algal growth and counteracting the growing acidity of the oceans, which many analysts see as one of the most pernicious long-term effects of increasing CO2 in the atmosphere.

The challenge of adding carbonates is to find a way of doing so that does not require exorbitant amounts of energy to mine, crush and transport the rocks.

The science of altering the world’s natural systems is called geo-engineering. Once on the whacky fringes of scientific research, the subject is rapidly becoming mainstream, attracting serious attention from academics and governments.

John Holdren, chief scientific advisor to US president Barack Obama, said in public a few weeks ago: “It’s got to be looked at ... We don’t have the luxury of ruling [out] any approach.”

The debate has been intensified by a set of studies published last week in the journal Nature. They concluded the world had little chance of holding temperature rises to 2ºC – a level widely regarded by scientists as the limit of safety, beyond which climate change becomes irreversible and potentially catastrophic. Such a level of warming risks leading for example to the melting of permafrost in Siberia, so releasing large quantities of methane, in turn causing stronger and more rapid warming.

Most suggestions for geo-engineering fall into one of three categories. Some of the most outlandish would block out the sun’s rays using mechanical means – a sunshade or mirror, for instance. These would be enormously expensive, even if possible.

Some of the most promising proposals involve ways to increase the Earth’s ability to reflect sunlight back into space. Sulphur particles shot into the stratosphere, could reflect enough sunlight to make a measurable difference. There is a problem – sulphur causes acid rain. Proponents point out much less sulphur would be needed than pours from dirty power stations, but objections are still likely.

A cheaper and less controversial method would be to spray seawater into the air from boats. This creates clouds made up of smaller than usual droplets of water, which are more reflective. Prof Salter says a drawback would be that, as well as reflecting sunlight, clouds trap infra-red heat on Earth.

But he says the net benefit would be huge – each drop would reflect 20bn times the amount of energy used to make it. He estimates that a fleet of about 500 ships would be needed, costing about £1m each.

Scientists are also exploring removing carbon from the atmosphere. One way is to fertilise the oceans with iron, so plankton grows and absorbs carbon. Less realistic are enormous air “scrubbers” – banks of sails coated with chemicals that react with CO2. Two unsolved problems are mastering the chemical absorption, and the sheer amount of energy that would be needed to propel vast volumes of air.

Employing geo-engineering would not remove the need for deep emissions cuts, Prof Salter warned: “No one in geo-engineering would argue that. We think it’s very important to get emissions down.” The two must be pursued in tandem, or rising emissions would counteract the benefits of the Earth-altering projects.

Tim Lenton, professor of Earth system science at the University of East Anglia, who conducted a review of geo-engineering methods, said scientists must beware of “tinkering with a system you do not fully understand”. For instance, he said, studies showed that putting sulphate aerosols into the atmosphere caused drying in vulnerable regions such as the Sahel and India.

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