Radical ideas to save the planet

Alok Jha
The Guardian,
Monday September 1 2008

Artificial clouds to reflect away sunlight, creating colossal blooms of oceanic algae, and the global use of synthetic carbon-neutral transport fuels - just three of the climate-transforming technologies in need of urgent investigation, according to leading scientists. The group argues that, with governments failing to grasp the urgent need for measures to combat dangerous climate change, radical - and possibly dangerous - solutions must now be seriously considered.
Air
Some of the most extreme ideas for climate engineering involve reducing the sunlight falling on the Earth's surface. Ken Caldeira of the Carnegie Institution in Stanford calculates that reflecting just 2% of the sun's light from the right places on Earth (mainly the Arctic) would be enough to counteract the warming effect from a doubling of CO2 in the atmosphere.
One approach is to insert "scatterers" into the stratosphere by deploying jumbo jets to deposit clouds of particles, such as sulphur dioxide. About 1m tonnes of sulphur dioxide a year across 10m sq km (3.8m sq miles) of the atmosphere would be enough to reflect away sufficient amounts of sunlight.
Another study proposes building ships that could spray micrometre-sized drops of seawater into the air under stratocumulus clouds to make them whiter.
Ocean
The growth of marine algae and other phytoplankton captures vast quantities of carbon dioxide from the atmosphere, but growth is often limited by a lack of essential nutrients. Adding such nutrients, such as iron or nitrates, to stimulate growth was studied by a team led by Richard Lampitt of the National Oceanography Centre in Southampton. The organisms incorporate atmospheric CO2 as they grow and, when they die, sink to the bottom of the ocean, taking the carbon with them. However, there is a moratorium around the world on iron-seeding experiments.
Wild cards
Other ideas considered by scientists, though not in the papers published today, include scrubbing carbon dioxide directly from the atmosphere. Klaus Lackner of Columbia University has designed a machine that could, if built to full scale, take up the CO2 emissions of 15,000 cars. With about 250,000 such machines, as much CO2 could be removed from the atmosphere as the world is currently pumping into it. The gas could then be stored underground or used in manufacturing. An idea further into the realms of the fantastic involves using shiny spacecraft to block sunlight. Scientists have suggested a constellation of free-flying craft that would sit between the sun and Earth. The only problem: it would cost around $100bn (£54.9bn) a year.