Sinking in,slowly

Oceans and forests are becoming less able to absorb CO2...

In the race to reduce greenhouse gases in the atmosphere,scientists have been looking to forests and oceans to absorb the pollution people generate. Relying on nature to compensate for humans excesses sounds like a win-win situationexcept that these resources are under stress from the very emissions we are asking them to absorb,making them less able partners in the pact.

Consider it the latest inconvenient truth about climate change. The benefits of these natural carbon sinks are many: their diverse ecosystems soak up carbon dioxide. Whats more,the international carbon market means that industries can compensate for their emissions at a fraction of the price of installing cleaner technology,essentially by investing in forests; meanwhile,poorer countries that are rich in woodland profit from selling not lumber but carbon credits.

Now,a global society of conservation biologists has launched a lobbying campaign,asking key decision-makersfrom the Danish officials chairing the climate talks in Copenhagen to US lawmakersto push for steeper emission cuts to ensure that humans do not exhaust forests capacity to store carbon in the decades to come.

Earlier this year,a team of nearly 70 researchers published a paper in the journal Science showing that the drought-stressed Amazon rain forest emitted roughly as much carbon dioxide in 2005 as it usually storesabout the same amount as the European Union and Japan together emit in a single year.

This dramatic new information confirms that unsustainable human demands on the Earths dwindling primary and old-growth forests have pushed them to the wall, said Dominick DellaSala,president-elect of the Society for Conservation Biologys North America section.

A separate article published last month in the journal Nature analysed the seas uptake of carbon between 1765 and 2008,finding that the proportion of fossil-fuel emissions absorbed by the oceans since 2000 may have declined by as much as 10 per cent.

The studys lead author,Samar Khatiwala,an oceanographer at Columbia Universitys Lamont-Doherty Earth Observatory,said oceans are becoming more acidic as more carbon dioxide enters the atmosphere,so they are losing their ability to soak up emissions produced by people.

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What our ocean study and other recent land studies suggest is that we cannot count on these sinks operating in the future as they have in the past and keep on subsidising our ever-growing appetite for fossil fuels, Khatiwala said.

According to the Global Carbon Project,which tracks emissions,land and ocean carbon sinks took up 57 per cent of human-generated carbon emissions between 1958 and 2008. While the size of these sinks has expanded in the past few decades,their absorption rate is slowing as greenhouse gas emissions have risen by 41 per cent since 1990.

Some environmentalists argue that the fact that forests are becoming less efficient carbon sponges should not lessen the incentive for preserving long-standing forests in developing countries. Such forests are more effective at storing carbon because the trees are bigger.