Adopted on December 12, 1997 by 159 countries at Kyoto, Japan, the protocol commits developed countries to cut emissions of these gases by five percent by 2008-2012 on the basis of their 1990 emissions.

Six gases are targeted -- carbon dioxide, methane, nitrous oxide, sulphur hexafluoride, the perfluorocarbon CF4 and a group of hydrofluorocarbons.

These carbon-laden substances act as an invisible blanket, preventing the heat of the Sun which accumulates on Earth from radiating back into space.

In turn, the atmosphere gets warmer, threatening to melt at least part of the polar ice caps, with potentially disastrous results.

The protocol sketches three mechanisms to cut the cost of meeting the target for industrial countries and help developing countries, which are exempted from the quotas.

These mechanisms, whose application is at the centre of the Bonn talks, go by the name of emission permits (TEP), clean development mechanisms (CDM) and joint implementation (JI) initiatives.

In plain language, they would set up the world's first market in greenhouse-gas emissions.

Under this, industrialised countries would obtain emission reduction credits if they help developing countries to build clean installations.

And heavy polluters would be able to buy emission reduction credits from other less-polluting industrial countries in order to meet the Kyoto targets.

The protocol has been ratified by only 15 small countries, and is not yet in force.

It provides for differentiated reductions -- seven percent for the United States, six percent for Japan, zero percent for Russia and eight percent for the European Union (EU), which shared the load among its members.

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