Attemps to slow down climate change by large-scale geo-engineering present ”serious risks” and are unlikely to replace the need to cut greenhouse gas emissions, Australia’s chief scientist has warned.
In an overview of schemes proposed by scientists, researchers at the Office of the Chief Scientist say the main methods of planetary-scale engineering would confront big problems with technical feasibility, political co-operation and cost. But research should be pursued in the hope of developing last-ditch methods to slow climate change.
”Given the difficulty in implementing global action to reduce CO2 emissions from human activities and their continued growth, geo-engineering is one possible approach to combat global warming,” it said.
”Geo-engineering would not moderate all the effects of rising emissions, and will introduce its own risks and uncertainties.”
Humans already play a role in dictating the Earth’s climate by adding greenhouse gases to the atmosphere - raising carbon dioxide levels by about 40 per cent since the Industrial Revolution - and by clearing forests to reduce the amount of carbon the land absorbs. But the deliberate management of global climate is still confined to theory, backed by a few small-scale experiments.
The report divides geo-engineering solutions to climate change into two basic types - plans to suck carbon dioxide out of the atmosphere and plans to block some of the sun’s heat before it gets here.
They include fertilising the oceans with iron filings, to stimulate the growth of algae, which absorbs CO2 and then sinks to the ocean floor, and sowing the atmosphere with sulphates, which deflect some of the sun’s rays away from Earth.
The simplest way to remove carbon from the air is the planting of forests on a massive scale but the limitations of suitable land, water and nutrients mean it can only play a small part in reducing emissions. ”Estimates suggest that, at best, about 2 to 4 per cent of greenhouse gas emissions from human activities could be offset this way,” the report said.
Ocean fertilisation is also likely to be ineffective on a large scale, and the best estimates suggest only a few per cent of human emissions could be offset this way, the report concluded. This is because many marine organisms feed on algae, ultimately returning its CO2 to the surface, because the ocean waters mix together, bringing deep water back to the surface. There would also be unknown side effects on fish.
Like efforts to absorb more CO2, efforts to shield the planet from some of the sun’s rays would need to be kept up more or less forever, lest there be a sudden surge of extra heat.
Releasing sulphate aerosols into the upper atmosphere is one method canvassed in the chief scientist’s report. The cheapest and most effective technique of doing this could be connecting long tubes to a sulphate source and raising them into the atmosphere by means of balloons.
But the potential drawbacks are many, including reducing rainfall over land masses, hampering the regeneration of the ozone layer and causing acid rain. If the scheme failed or was stopped, temperatures would rise very quickly.
The findings of the Australian report are similar to those of recent studies undertaken by Britain’s Royal Society and the US Task Force on Climate Remediation Research.