Negotiators from more than 150 countries have begun another round of talks on climate change.

The talks involve the signatories to the Kyoto Protocol, the climate treaty agreed in outline in Bonn last July.

This round, in Marrakech in Morocco, has to translate Bonn's political agreement into a legal instrument.

The negotiators hope to pave the way for the protocol's ratification next year.

The Bonn agreement commits signatories to reduce their emissions of six of the greenhouse gases believed to be intensifying the climate's natural variability.

By between 2008 and 2012, they will have to cut emissions by around 2% on 1990 levels. An earlier draft demanded cuts averaging 5.2%, but it was modified in the face of strong US opposition.

The US later repudiated the treaty entirely, saying it would harm its economy.

Modest start

Many climate scientists say the world must cut emissions of the main gas caused by human activities, carbon dioxide, by at least 60% on present levels by mid-century.

Critics say Kyoto is a waste of money and will make very little difference. Its defenders say it is a first step opening the way to far more ambitious agreements.

The Marrakech meeting, known as COP7 (the seventh conference of the parties) has to write the rule book for Kyoto, in the hope that enough signatories will ratify it, at next year's World Summit on Sustainable Development, for it to enter into force.

That means it must have been ratified by 55 countries, responsible for 55% of emissions in 1990. But several countries will wait to see what Marrakech agrees before deciding whether or not to ratify Kyoto.

WWF, the global environment network, is concerned that Marrakech "resists attempts by Australia, Canada, Russia and Japan" to reopen debate on issues agreed in Bonn.

No going back

Jan Pronk, the Dutch environment minister who chaired the Bonn meeting, told delegates in Marrakech: "Do not reopen the political compromises we've reached. Apply them."

Among the key issues are:

• accounting for, reporting and verifying countries' emissions
• enforcing compliance with the rules, and fixing penalties for breaking them
• deciding how much pollution can be absorbed by forests and soils
• the rules for buying and selling unused emission rights
• how to channel money to developing countries to help them to cope with changing climate and to install energy-efficient technology.

Some of the protocol's defenders still hope Washington will endorse it.

Tony Juniper of Friends of the Earth said: "The world has rightly shown its solidarity with the people of the US after the appalling crimes of 11 September.

"Tony Blair must now use his influence with President Bush to persuade him to show his solidarity with the rest of the world by tackling climate change."

But Philip Stott, professor of biogeography at the University of London, UK, a longstanding climate change sceptic, sounded a different note.

"Let's hope all those eager delegates who will be at COP7 actually take time to study the temperature history of where they're visiting - there's no 'global warming' at all in Morocco", he said.