forests and farmlands cannot be relied on to soak up greenhouse gases, says a recent report released by the uk Royal Science Society. It says the cuts in emissions are the only long-term way to reduce global warming over long-periods.

The report says too little is known of the science of so-called land carbon-sinks, which sequester carbon dioxide. Carbon sinks will be a major issue in Bonn, Germany, next week when environmentalists and policy-makers resume climate negotiations, which have been jeopardised by the withdrawal of the United States from the Kyoto agreement on global warming.

In its report, the uk- based independent body of top scientists said better methods are needed to verify the impact of carbon sinks on global warming. The impact of many management practices on emissions of other trace greenhouse gases such as methane and nitrous oxide is poorly understood. Until it is possible to calculate the impacts and the decipher the science of sequestering completely, the report recommend that land carbon sink projects likely to result in significant emissions of trace gases, such as the large-scale use of nitrogen-based fertilisers be avoided.

The report further adds that existing techniques of monitoring quantifying and verifying land carbon sinks established under the Kyoto Protocol have too many unexplained elements. There is an urgent need to increase the accuracy of these techniques before land carbon sinks are utilised to any significant extent, the report urges.

It suggests that the reducing of the amount of carbon dioxide from burning fossil fuels should be the main way to reduce global warming. "These carbon sinks are of rather limited size and also will only work for a relatively short duration, a few decades. That means they can't make a major contribution to reducing carbon emissions and solving the global warming problem,' says John Shepherd, co-author of the report.

Carbon sinks and soil absorb about 40 per cent of carbon dioxide emissions and could soak up as much as 45 per cent. But, the maximum that could be absorbed would only be a quarter of that needed by 2050 to prevent major rises in global temperature. "Our view is that the argument is being diverted into what is really a rather unproductive area and people should get back to talking about carbon emission reductions by use of renewable fuels,' says Shepherd. The report also warns that in the future carbon sinks could become a source of carbon dioxide emitter. They could release greenhouse gases, such as methane. The long-term solution must be cuts in carbon dioxide emissions through energy saving and replacing fossil fuels with renewable and nuclear energy.