Dutch Professor Paul Crutzen won the Nobel Prize for chemistry when he
discovered the causes of the hole in the ozone layer. His plan is to
fire hundreds of rockets loaded with tons of sulphur into the
stratosphere, creating a vast, but very thin, sunscreen of sulphur
around the Earth.

British atmospheric physicist Professor John Latham and engineer Stephen
Salter have designed a fleet of remote-controlled yachts. These would
pump fine particles of sea water into the clouds, increasing the
thickness of the clouds and reflecting the sun's rays.

Others want to tackle the problem of excess carbon dioxide – the cause
of global warming. Sydney engineer Professor Ian Jones proposes to feed
plankton – tiny plants and animals that live in the sea – with tons of
fertiliser. This will make the plankton grow and absorb carbon dioxide
from the air.

New York-based Professor Klaus Lackner has designed a machine to capture
carbon dioxide. His plan is to locate them across the globe where they
would suck in carbon dioxide, turning it into a powder to be buried deep
under the ocean in disused oil or gas fields.