OTTAWA — If all else fails in the battle to curb global warming, there's always the big umbrella  in space.

Governments should consider proposals to put a huge barrier in space to block sunlight if conventional efforts to curb rising temperatures don't succeed, says a draft report by the UN Intergovernmental Panel on Climate Change.

Scientists believe that such "geo-engineering techniques,'' however far-fetched they sound, could  be used to buy time if worst-case ecological predictions are realized.

A sun-blocking disk would cover an area of 106 square kilometers, weigh 3,000 tonnes and would spin continually. It would be built over time by a space shuttle, says the draft IPPC report. Construction would require one shuttle flight annually for 100 years.

Another proposal, which some liken to an artificial volcano, calls for controlled scattering of tiny sulphur particles in the atmosphere, to reduce sunlight reaching the planet.

Nobel prize-winning scientist Paul Krutzen has advocated this as the safest of the unconventional techniques that are being considered, since natural volcanic eruptions are known to produce a cooling effect which is reversible.

"These schemes do not affect the expected escalation in global carbon dioxide levels but could reduce or eliminate the associated warming,'' says the draft study, which could still undergo major revisions before its scheduled release next month.

How about fertilizing the oceans with iron? Crazy as it sounds, this idea has been the subject of at least 11 studies in different parts of the world, including one in Canada, and is considered to have some promise.

Iron is a nutrient for phytoplankton that live in upper levels of the ocean. These microbes have the property of absorbing carbon. The theory is that scattering iron in the water would stimulate their growth, producing higher rates of carbon absorption.

Gordon McBean, president of the Canadian Foundation for Climate and Atmospheric Science, says these unconventional approaches need to be studied because governments will want to know which options have promise.

Unconventional techniques are generally considered in terms of a "last-ditch'' situation -- for example if it became clear that the Greenland ice fields were at severe risk of disintegration, which would cause a catastrophic rise in sea levels.

The panel also discussed the idea of carbon sequestration -- removing carbon from emissions and burying it in the ground in sealed geological cavities. That is already being done in a few places around the world, including Saskatchewan.