Meteorologists opened the World Climate Conference on Monday in what a US official called a "critical" attempt to share information globally and help communities worldwide adapt to climate change.

Some 2,500 experts gathered against the backdrop of troubled negotiations to strike a global agreement on climate change at another conference in Copenhagen in December, which are marked by a rift between rich and poor nations.

The Geneva conference would discuss how to boost long-term weather and climate forecasting, especially in Africa and developing nations, said Michel Jarraud, director general of the UN's World Meteorological Organisation (WMO).

"We have now come to the point that we feel there is a major gap that needs to be filled," he told journalists.

The proposed "Global Framework for Climate Services" under discussion in Geneva could shape decisions on water, agriculture, fisheries, health, forestry, transport, tourism, energy, and preparations for natural disasters.

It would largely build on successful, existing international cooperation on weather forecasting to expand the scope of climate predictions, Jarraud said.

Instead of looking at timescales of days and sometimes weeks ahead, the aim was to "extend the window" and produce forecasts that look seasons and even decades ahead, a US weather official explained.

The Geneva conference is not part of the Copenhagen process, which includes talks on steps to help countries prevent or adapt to the impact of more extreme weather conditions produced by global warming, including finance for poor nations.

But officials said that by allowing all countries to access information that would help them assess and adapt to changing temperatures, humidity levels, storm and wind patterns, it would provide a key building block.

The outcome of the five-day meeting was "critical to coping with climate variability," White House associate director for environment Sherburne Abbott told reporters in Geneva.

After years of scepticism on climate change under the administration of former president George W. Bush, the United States had turned up with a 50-strong delegation.

And they were intent on "sharing a large amount of information with the developing world," Abbott said.

During the conference scientists will take the opportunity to swap the latest research on issues such as the warming of the Arctic Circle and the potential social and economic impacts of climate change.

The WMO has warned that global warming is transforming thinking on issues such as flood defences, farming or power generation, which have often relied on experience of past weather patterns and sea levels.

"Now we need to anticipate change," said Jarraud before the conference. "We can no longer base ourselves on the past to take decisions for the future."

The proposed framework is also aimed at improving forecasts of localised effects that can be much harsher than those predicted at a national or global level, especially in mountain and coastal areas.

About 15 heads of state or government mainly from from African, European and island states, as well as several dozen ministers, are due to attend from Thursday, led by UN Secretary General Ban Ki-moon and Chinese Vice Premier Hui Liangyu.

The United Nations has only held two World Climate Conferences before, the last of which was 19 years ago.

The first, in 1979, was credited with pinpointing a problem with carbon build-ups in the earth's atmosphere and setting in motion a global approach to climate research.

And that ultimately produced the panel of international scientists which provided groundbreaking scientific evidence of climate change -- and of humanity's influence on global warming.