Sir

As your News Feature “The carbon game” (Nature 432, 268–270; 2004) makes clear, the start of the European Emissions Trading Scheme may be a route to controlling greenhouse gases. Coupled with the United Nations' Clean Development Mechanism to encourage participation by the poorer nations, it may indeed work.

However, independent atmospheric verification of emissions has long been neglected. The system relies on producers reporting their own greenhouse emissions. Until now, there has been no financial penalty for producing emissions and no benefit from carbon sequestration. Now that money enters the picture, so also can fraud.

Today's emitters of greenhouse gases report their emissions; the information is then passed on to national and international databases. Under the new scheme, there will now be an incentive to under-report emissions at every stage. Equally, those sequestering carbon will be tempted to exaggerate. Despite diligent independent controls, doubts will arise at all levels. Even when there is no intent to misreport, companies, regions and nations will suspect each other.

“Trust but verify” as Ronald Reagan used to say, quoting a Russian motto. The Nuclear Test Ban Treaty created trust by diligent verification. Atmospheric monitoring detected fallout, and a global network of seismographs was set up in order to detect explosions. Trust came, bomb tests ended. Plate tectonics was a surprise bonus.

The Kyoto Protocol lacks this. Verification is not expensive, but atmospheric monitoring at present is inadequate. A modest but effective multinational programme to assess net carbon-gas emissions would not cost much. Satellites give broad-brush imagery, but the main need is for very precise measurements on the ground, which are not expensive to carry out. For methane, modelling based on careful monitoring of concentrations and isotopes is already verifying national emission inventories by source type and seasonality.

Most of the monitoring load falls on the United States. There are a few exceptions in the form of some excellent national programmes, and the European Union has programmes such as CarboEurope. But many non-US programmes have only short-term funding, despite the need for continuity. The British contribution is minimal. There is little on the tropical landmasses.

Other nations must do more to share in detailed long-term understanding of carbon budgets, including uptakes by the terrestrial biosphere. The Commonwealth ‘club’, led by strong Australian and Canadian programmes, could help in the tropics.

To win the trust of the United States, China and India, whose emissions growth will damage us all, we need to verify emissions and uptakes accurately and in detail.