The world should not only have to cut down carbon emissions drastically to avoid dangerous climate change — an overarching notion that the IPCC put out in a session devoted to the possible contours of the next (fourth) assessment report — but have to do it with a great sense of urgency. David Carson, director, World Climate Research Centre, argues that using forests as sinks may work only in the short-term. Models predict that, by 2050, most forests should have exhausted their capacity to absorb carbon, and eventually become sources of carbon. Furthermore, explains W Steffen, executive director, International Geosphere-Biosphere Programme, given the complex nature of the carbon cycle, it would be difficult to assess the precise impact of CDM projects on carbon concentrations in the long run.

The billion dollar question is: should policymakers wait for scientists to tell them upto a reasonable degree which of the many scenarios thrown up by climate models is most likely, or should they go ahead, taking a worst-case scenario as the most likely one. Scientists say they can’t discriminate between science and value judgement, and it is up to each country to decide what seems reasonable to them.

The fourth assessment report, to be completed by 2007, would try to narrow the range of choices available to the policymaker. But Carson feels it will be really difficult to achieve this in the two years they have been given — all studies must have concluded by 2004, the next three years being reserved for peer review. The next assessment will also focus on regional impacts of climate change which, along with climate change predictions, will give policymakers a rough yardstick to plan the development of their respective countries. Steffen says a better understanding of regional climate change could provide a basis for climate justice. "For instance, there is growing evidence that the Sahelian drought of the 1970s was caused by aerosols emitted in the North American region. If established, the affected victims could sue the culprits for endangering their survival," he says.

It could be a while before scientists put together the jumbled pieces of the climate jigsaw. But people like Steffen and Carson would like policymakers to err on the side of caution, simply because it’s already too late. "Had we heeded the early warnings in the 1970s, we would have been in a better position to tackle climate change," Carson says.