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By Jeremy Lovell

LONDON, Nov 19 (Reuters) - Prime Minister Gordon Brown on Monday promised Britain would take tough measures to fight the climate crisis and urged other world leaders to follow suit.

Two weeks before a meeting of U.N. environment ministers on the Indonesian island of Bali to try to start urgent talks on finding a replacement to the Kyoto Protocol on cutting carbon emissions, Brown said concerted action was crucial.

Kyoto, which took a decade to negotiate and bring into force, expires in 2012 and so far there is nothing to replace it and no agreement on what any follow-on treaty should contain, with the United States and China in particular at loggerheads.

"The climate change crisis is the product of many generations, but overcoming it must be the great project of this generation. And it will have to involve not just Europe and America but the entire community of nations," Brown said.

In his first major speech on the climate, Brown recommitted Britain to limiting the rise in global temperatures to two degrees above pre-industrial levels and endorsed the European Union's target of getting 20 percent of energy from renewables.

He said it was vital that the world's developed nations, who have produced most of the climate changing carbon gases, take the lead in committing to tough curbs on their emissions -- including the United States which has so far refused.

"Our vision has one overriding aim: holding the rise in global average temperature to no more than two degrees centigrade," Brown said.

"This requires global greenhouse gas emissions to peak within the next 10 to 15 years and be cut at least by half by 2050," Brown told a meeting hosted by environment group WWF.

CAUTIOUS WELCOME

Environmental groups cautiously welcomed the speech, noting that while it said little new it showed strong commitments to policies from which some major nations have begun to back away.

"He is finding his voice on this issue. This is all about transformation and building a green economy," said Steve Howard of the Climate Group, a body that advised business on cutting emissions of climate warming carbon gases.

"If every G8 leader talked like this the world would be in a better place than we are now," he added.

Scientsts say average world tempertures will rise by between 1.8 and 4.0 degrees Celsius this century due to burning fossil fuels for power and transport, causing floods, droughts, famines and putting millions of lives at risk.

Brown, who took over as prime minister from Tony Blair in June, has not been renowned for his green credentials.

But he repeated a pledge he made in September to get a committee that will be set up under the Climate Change Bill published last week to study whether Britain should set a legal target of cutting its carbon emissions by 80 percent by 2050 instead of the 60 percent set out in the legislation.

But while noting the scale and urgency of the crisis, Brown also underscored the job and business opportunities it offered.

"Globally, the overall added value of the low carbon energy sector could be as high as three trillion dollars per year worldwide by 2050," he said. The industry could create 25 million new jobs, including a million in Britain. (Reporting by Jeremy Lovell; editing by Peter Millership)

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