Three days of talks involving environment officials from more than 100 countries have ended in Colombia with a top United Nations official admitting that global environment treaties are having little effect.

	1. Burning of fossil fuels increases atmospheric levels of carbon dioxide and other greenhouse gases 2. These trap some of the sun's energy and reflect the heat back down to earth. 3. Some scientists argue increased levels of greenhouse gases leads to overheating, causing global warming Click here for animated graphic showing the Greenhouse Effect

The head of the UN environment programme, Klaus Toepfer, told journalists that most protocols were proving ineffective because they were voluntary.

His comment came a day after US President George Bush outlined his alternative to the Kyoto treaty on climate change, saying he would give tax concessions to US businesses who reduce emissions.

Correspondents say Mr Bush's announcement overshadowed the Colombia gathering, which was held to discuss an agenda for the UN development summit later this year.

However, the conference saw a rare agreement between Israel and the Palestinian Authority.

The warring sides agreed to assess the environmental damage done in the West Bank and Gaza Strip through pollution of water supplies and waste dumping.

"If we are to live together on this piece of land, we need to respect the shared natural resources here," said the Palestinian Environment Minister, Yousef Yousef Abu Safiehm.

Mixed reaction

Proposals by President Bush to tackle global warming have provoked a mixed reaction at home and abroad.

Bush's proposals

Cut ratio of emissions to US GDP growth by 18% over 10 years Tax incentives to reduce sulphur dioxide, nitrogen oxides and mercury emissions Increase 2003 budget by $700m to $4.5bn to fund initiatives

As an alternative to the Kyoto accord, which he rejected last year, Mr Bush is proposing tax incentives to encourage industry to reduce greenhouse gas output on a voluntary basis.

Critics have said the plan is a concession to big business and a "hollow attempt" to shift responsibility for cutting greenhouse gas emissions onto developing nations.

Japan's Environment Minister Hiroshi Oki said he appreciated Mr Bush's efforts, but Tokyo was still not satisfied that they went far enough. Japan hosted talks that led to the Kyoto accord.

Mr Bush said the Kyoto treaty would have put millions of people out of work because of its mandatory reductions.

It was unfair, he said, because it would have penalised the US and exempted many developing countries such as India and China.

The main difference between the Bush initiative and the Kyoto treaty is that it proposes goals rather than mandatory reductions and a relative rather than net reduction in emissions.