FACTBOX: What is the Kyoto Protocol?

(Reuters) - Delegates from up to 190 nations will meet in Bangkok from March 31-April 4 to start work on a new U.N. pact to fight climate change and succeed the Kyoto Protocol.

Here are some frequently asked questions about Kyoto:

* WHAT IS THE KYOTO PROTOCOL?

-- It is a pact agreed by governments at a 1997 U.N. conference in Kyoto, Japan, to reduce greenhouse gases emitted by developed countries to at least 5 percent below 1990 levels by 2008-12. More than 170 nations have ratified the pact.

* IS IT THE FIRST AGREEMENT OF ITS KIND?

-- Governments agreed to tackle climate change at an "Earth Summit" in Rio de Janeiro in 1992 with non-binding targets. Kyoto is the follow-up.

* SO IT IS LEGALLY BINDING?

-- Kyoto has legal force from February 16, 2005. The United States, long the world's biggest source of emissions but which is being surpassed by China, came out against the pact in 2001. President George W. Bush reckoned it would be too expensive and wrongly omits 2012 emissions targets for developing nations.

* HOW WILL IT BE ENFORCED?

-- Countries overshooting their targets in 2012 will have to make both the promised cuts and 30 percent more in a second period from 2013.

* DO ALL COUNTRIES HAVE TO CUT EMISSIONS BY 5 PERCENT?

-- No, only 37 relatively developed countries have agreed to targets for 2008-12 under a principle that richer countries are most to blame. They range from an 8 percent cut for the European Union from 1990 levels to a 10 percent rise for Iceland.

* WHAT ARE 'GREENHOUSE GASES?'

-- Greenhouse gases trap heat in the earth's atmosphere. The main culprit from human activities is carbon dioxide, produced largely from burning fossil fuels. The protocol also covers methane, much of which comes from agriculture, and nitrous oxide, mostly from fertilizer use. Three industrial gases are also included.

* HOW WILL COUNTRIES COMPLY?

-- The European Union set up a market in January 2005 under which about 12,000 factories and power stations are given carbon dioxide quotas. If they overshoot they can buy extra allowances in the market or pay a financial penalty; if they undershoot they can sell them.

* WHAT OTHER MECHANISMS ARE THERE?

-- Developed countries can earn credits to offset against their targets by funding clean technologies, such as solar power, in poorer countries. They can also have joint investments in former Soviet bloc nations.

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(Editing by David Fogarty)