Oct 4, 2010
By Michael Richardson, For The Straits Times
WHEN Mount Pinatubo in the Philippines exploded in 1991, the effects were terrifying. It was the second-largest volcanic eruption of the 20th century and the biggest in a densely populated area.
Advance warning saved thousands of lives before avalanches of molten ash and mud roared down the flanks of the mountain, filling once-deep valleys with volcanic deposits up to 200m thick and displacing more than 200,000 people.
The ash from the eruption rose 35km into the air in a menacing cloud hundreds of kilometres wide.
But something else was observed and noted by scientists.
Nearly 20 million tonnes of sulphur dioxide gas were injected into the upper atmosphere where they combined with other materials to form tiny sulphuric acid particles. These sulphate aerosols acted as a giant sunshade, reflecting solar radiation back into space and thus cooling Earth's surface.
Dispersal of the aerosols worldwide in the jetstream caused global temperatures to drop temporarily by 0.5 deg C for about two years. This was not far short of the rise in average land and sea surface temperature since the start of the industrial revolution.
As climate change officials resume international negotiations today in the Chinese city of Tianjin, there is little sign of progress on a binding agreement to take the costly steps needed to reduce the emission of global warming gases from human activity.
The scientific panel advising the United Nations has warned that without such cuts, the temperature could rise by as much as another 4 deg C by the end of the century, increasing the risk of dangerous climate change.
With an effective accord on carbon cuts unlikely any time soon, more scientists and officials are looking to Plan G - geoengineering - to cool the planet.
This essentially consists of large-scale alterations to the atmosphere, land or oceans to counter the effects of global warming. In the latest sign of growing interest in these controversial techniques, a group of climate scientists met in Washington last week to debate 'Geoengineering: The Horrifying Idea Whose Time Has Come?'
The Royal Society, Britain's national academy of science, added impetus to further funding and study of geoengineering when it published a report last year. It concluded that unless future efforts to slow greenhouse gas emission are much more successful than they have been so far, additional action will be necessary.
However, the report cautioned that there were major uncertainties about the effectiveness, costs and environmental impact of geoengineering technologies.
Still, the debate seems set to intensify. The first of two reports requested by the United States Congress is due to be released this month, identifying research capabilities of different US agencies and outlining how an inter-agency programme might be structured.
At about the same time, the US House of Representatives science committee will release a report, prepared in conjunction with Britain's Parliament, on relevant geoengineering policy issues.
Meanwhile, the European Union has funded a German research group to study the physics, ethics and geopolitical aspects of manipulating the climate system.
The US space agency, Nasa, has said that geoengineering could provide a way to slow global warming until carbon emissions can be reduced enough to prevent catastrophic climate change.
Many geoengineering schemes have been proposed. One of the most feasible involves mimicking volcanoes by injecting sulphate aerosols or their precursors into the stratosphere. The hope is that, like the eruption of Mount Pinatubo, such actions may cool the atmosphere.
Another geoengineering project is to add fertiliser to selected regions of the ocean to increase phytoplankton growth to remove more carbon from the atmosphere.
Critics worry about the side-effects of both. Fertilising the seas could cause ocean dead zones and toxic blooms that would harm fish and other aquatic life.
Adding large amounts of sulphate aerosols to the upper atmosphere could cool the planet, stop the melting of sea ice in the Arctic and land-based ice sheets in Greenland and Antarctica, slow sea level rise, and increase the capacity of plants to absorb carbon dioxide.
But it might also reduce Asian monsoon rainfall, deplete Earth's protective ozone layer, and reduce the amount of sunlight for solar power. It would also blur the skies, hamper Earth-based optical astronomy, erode the incentive to cut greenhouse gas emissions, and do nothing to stop ocean acidification that threatens sea life.
Quite apart from the high cost, there is the sensitive geopolitical issue of who should control geoengineering activity and decide where and how to apply the most promising technology.
Scientific studies have shown that although the average global temperature could be lowered by seeding the stratosphere with sulphates, some regions might remain too warm afterwards while others would cool too much.
Mr Pete Irvine, a climate scientist at Bristol University and the lead author of one of the latest studies on the impact of geoengineering, cautions that there are likely to be disagreements between countries and regions over any future schemes.
'If there is a large amount of global warming in the future, there would be no strength of geoengineering that would be best for everyone,' he said.
'Some may be better off without any geoengineering while others may do better with a large amount.'
If apportioning the burden of cutting greenhouse gases still causes acrimonious debate among governments after many years of negotiation, putting Plan G into effect is also likely to be fraught with contention.
The writer is a visiting senior research fellow at the Institute of Southeast Asian Studies.
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