The Kyoto Protocol allows reductions in emissions of several 'greenhouse' gases to be credited against a CO₂-equivalent emissions limit, calculated using 'global warming potential' indices for each gas. Using an integrated global-systems model, it is shown that a multi-gas control strategy could greatly reduce the costs of fulfilling the Kyoto Protocol compared with a CO₂-only strategy. Extending the Kyoto Protocol to 2100 without more severe emissions reductions shows little difference between the two strategies in climate and ecosystem effects. Under a more stringent emissions policy, the use of global warming potentials as applied in the Kyoto Protocol leads to considerably more mitigation of climate change for multi-gas strategies than for the—supposedly equivalent—CO₂-only control, thus emphasizing the limits of global warming potentials as a tool for political decisions.

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