Estimated global emissions of carbon dioxide fell in 1998 - the first sign that the pollution can be reduced while the world economy remains healthy.

BBC Science's Toby Murcott on the CO2 emission reduction

Reductions in emissions have happened before but only because economic disasters cut the amount of fuel burnt. In the 1970s, the oil crises made fuel very expensive and the economic collapse of Eastern Europe in the early 1990s shut many factories.

But the 1998 fall in emissions was the first to occur while the world economy was growing. The Worldwatch Institute says the fall results from improved energy efficiency, the growth of relatively low-energy industries like information technology, and falling coal use.

The fall will raise hopes that it may not be as difficult as critics believe for the world to honour its commitments under the Kyoto Protocol.

Since 1950, emissions have risen but increased efficiency means every gallon of fuel now creates more wealth

The Protocol is the international agreement on measures to tackle the threat of global warming. CO2 is the main gas produced by human activities that contributes to the warming.

Growing richer - and cleaner

The Worldwatch Institute, based in Washington DC, based its estimates on energy data supplied by BP Amoco.

Worldwatch says global emissions of carbon from the burning of coal, oil and natural gas fell in 1998 by 0.5% to 6.32 billion tons.

As the world economy grew last year by 2.5%, the Institute says this "suggests an accelerated 'de-linking' of economic expansion from carbon emissions". In the past, economic growth has been at the expense of increased fuel consumption and greater CO2 emissions.

The decline of coal pushes emissions downwards

Over the past two years, its report says, the global economy has grown by 6.8% while carbon emissions remained steady.

This means that the amount of carbon emitted in order to produce $1,000 of income has fallen by 6.4%.

However, the report says "it is not yet clear how long-lasting the new trend will be".

It says the drop was caused partly by improved energy efficiency and falling coal use, prompted by the removal of energy subsidies.

China, for instance, has cut its coal subsidies by $14 bn. Its economy grew by 7.2% last year, while emissions fell by 3.7%.

This compares with a steady 4% annual increase in emissions in the two previous decades.

USA off target

Poland showed a similar pattern, with emissions down by 9.7% and the economy 6% up.

Russia's emissions are now 24% below their 1991 level.

But the US registered a small increase in emissions of 0.4% while its economy grew by 3.9% last year.

The new technologies are energy misers

Its emissions were 11.7% higher than in 1990. It is committed to reducing its total greenhouse emissions to 7% below the 1990 level by 2010.

Clean screens

The report says another reason for the global fall in carbon is that much recent economic growth has been in information technologies and services, which are not prodigious users of energy.

"Operating the entire global Internet requires less electricity than New York City uses," notes the report.

Worldwatch says the report "will make it slightly easier to achieve the ambitious goals of the Kyoto Protocol".

"However, to reach those targets, and to reduce emissions in developing countries, accelerated adoption of new energy technologies will be needed."

The Institute of Economic Affairs, commenting on the report, said it was not clear that CO2 reductions were a cause for celebration.

Evidence that carbon was helping to warm the world was "pretty shaky", and small changes in CO2 output were "basically irrelevant".

The Association for the Conservation of Energy said the figures were "very welcome".

But a continuing cause for concern was "the way in which OECD countries' emission growth is continuing".