The Kyoto Protocol on climate change now has an official rulebook, agreed by delegates from more than 160 countries in Marrakech, Morocco.

The agreement, reached at a meeting that began on 29 October, was thrashed out in the early hours of 10 November, after a final 18-hour negotiating session. It has triggered optimism that the treaty will come into force before the World Summit on Sustainable Development, to be held next September in Johannesburg, South Africa.

Contentious questions in Marrakech included the eligibility of industrialized countries to buy and sell rights to emit greenhouse gases, methodologies for reporting and monitoring emissions and emission-reduction activities, and penalties for countries failing to achieve their emission targets.

To come into force, the Kyoto Protocol must be ratified by a minimum of 55 countries that together accounted for at least 55% of global carbon-dioxide emissions in 1990. The United States, the world's largest emitter, still says that it will not ratify the protocol.

This means that the European Union (EU) and the 'Umbrella Group' of industrialized countries — including Japan, Canada, Australia and Russia — are needed to reach the 55% emissions target. Although the EU is enthusiastic, members of the Umbrella Group have, until now, been reluctant.

To make ratification palatable to Russia, delegates agreed that credits for its natural carbon 'sinks', mainly forests, could be almost doubled to 33 million tonnes of carbon per year. Russia hopes to profit from unused rights to emit greenhouse gases, and now says it will ratify the protocol.

Japan also won concessions that will make market-based mechanisms, such as emissions trading, fully available to all industrialized countries, regardless of whether or not they meet their targets and report their emissions adequately.

But a decision on the legal status of penalties for countries that fail to meet their targets was deferred to the first meeting of parties after the treaty has come into force.