Sir, Nigel Lawson's promotion of his new book ("Stop this foolish overreaction to climate change", April 6) does his readers a disservice by ignoring the Stern review and the new literature on the risks of climate change. The review estimated the costs at between 5 and 20 per cent of world gross domestic product, depending on an assessment of the risks and treatment of the discount rate. The review used the ethical principle that the valuations of human lives and health should not be discounted at market rates, and this assumption, together with a better treatment of risk yielded much higher costs than the 1 to 5 per cent from earlier studies quoted in the Intergovernmental Panel for Climate Change report. Lord Lawson has not explained that the climate problem is one of stocks of greenhouse gases in the atmosphere, and since CO2 is a very long-lived gas, each tonne emitted gives rise to damage over the indefinite future. Since we are very likely to be experiencing damage at present, the outlook is that this will get progressively worse. Taking loss of life into account means that future costs are already likely to be immeasurable, and warrant strong urgent action for all of us, but most of all from governments acting together. Far from damaging the economy of Europe, the European Union's unilateral climate policies will improve the well-being of its citizens, and benefit its economy through development of new technologies, such as wind power, tc export to the rest of the world. However, the point of the EU policy is to support global action. Lord Lawson has also ignored the Stern review's and IPCC report's conclusions on the costs of mitigation. The literature suggests that these costs will be in the range of 1 per cent of GDP with a range of plus or minus 3 percentage points. The IPCC reports that world GDP could be higher if policies are well-designed and encourage technological co-operation. At this time of collapsing credit, concerted Group of Eight action to establish long-term prices of carbon, perhaps around $100 per tonne of CO2 by 2020, together with new standards and agreements for low-carbon technologies, would support new business investment and the global economy. Terry Barker, Co-ordinating Lead Author, Working Group 3 (Mitigation), Intergovernmental Panel for Climate Change, Director, 4CMR, Cambridge Centre for Climate Change Mitigation Research,