WHAT IS THE KYOTO PROTOCOL?

It is a pact agreed by governments at a 1997 UN conference in Kyoto, Japan, to reduce greenhouse gases emitted by developed countries by 5.2 percent of 1990 levels from 2008 to 2012. A total of 156 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. Kyoto is the follow-up and is the first legally binding global agreement to cut greenhouse gases.

SO IT'S LEGALLY BINDING?

Kyoto has legal force from Feb. 16, 2005. It represents 61.6 percent of developed nations' total emissions. The United States, the world's biggest polluter, has pulled out, saying Kyoto is too expensive and wrongly omits 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 5.2 PERCENT?

No, only 39 relatively developed countries have target levels for 2008-12 under a principle that richer countries are most to blame and so should take the lead.

HOW ARE THEY DOING SO FAR?

Rich nations' emissions were 5.9 percent below 1990 levels in 2003 but this was mainly due to a collapse of Soviet-era industries. Many other nations are above target -- US emissions were up 13.1 percent.

WHAT ARE THESE "GREENHOUSE GASES"?

Greenhouse gases trap heat in the earth's atmosphere. The main one is carbon dioxide, most of which comes from burning fossil fuel. The protocol also covers methane, much of which comes from agriculture, and nitrous oxide, mostly from fertiliser 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?