By Alex Kirby BBC News Online environment correspondent

Developed countries must start working urgently towards massive cuts in emissions of greenhouse gases, says a UK environmentalist group.

The call from the Royal Society for the Protection of Birds (RSPB) comes on the opening day of a climate conference in the Indian capital Delhi.

The conference brings together countries which have signed the Kyoto Protocol, the international agreement on tackling climate change.

The RSPB says emissions cuts of 60% must be implemented by the middle of the 21st Century to slow down global warming.

Developed countries have agreed so far to try to reduce greenhouse emissions to 5.2% below their 1990 levels.

Respected

The RSPB is respected for its work in the UK and abroad to conserve not only species but entire eco-systems, and the human societies that depend on them.

It is also respected for its analysis and its advocacy work.

Even so there may be surprise that it has joined others in speaking so forthrightly on climate change.

We do not have the luxury of standing by for years before the world gets round to making a serious attempt to cut its emissions.

John Lanchbery RSPB

The Kyoto Protocol enters into force after 55 countries, including developed countries responsible together for at least 55% of the rich world's 1990 CO2 emissions, have ratified it.

By early October 95 signatories, accounting for 37% of 1990 emissions, had ratified the protocol.

Officials of the UN Climate Change Convention (UNFCCC) expect Russia and other countries to ratify it soon, taking it beyond the critical 55% threshold.

US will not ratify

The US has signed the protocol but said last year it would not ratify it.

Those countries that do will be expected to achieve the 5.2% cut by between 2008 and 2012.

There is some doubt about how many will achieve even this modest goal. A report to the Delhi meeting will say that by 2000 emissions in the richest countries had actually risen by 8.4% on 1990 levels.

In the former Soviet Union and eastern Europe, by contrast, emissions had fallen by 38% as economies were plunged into crisis.

The Kyoto targets apply to six gases, which many scientists believe are adding to natural climate variability.

The most serious is carbon dioxide (CO2).

The Intergovernmental Panel on Climate Change (IPCC) represents the consensus view of government and other scientists.

Growing certainty

In successive reports it has said with growing certainty that human activities are contributing significantly to climate change, though some scientists continue to challenge this.

The RSPB said: "As carbon emissions continue to increase, it is increasingly clear that far more has to be done in order to stabilise greenhouse gas concentrations at a low level and slow down global warming.

"Unless the world now goes far beyond the Kyoto targets, the ultimate objective of the climate convention - that human-induced climate change should be limited to a level that allows ecosystems to adapt naturally - will have been broken.

'Need for action'

"There is a need for action by everyone. Not only must developed countries take the lead in cutting their emissions: the developing countries also need to act."

John Lanchbery of the RSPB said: "We do not have the luxury of standing by for years before the world gets round to making a serious attempt to cut its emissions. The next few years will be critical."

The Delhi meeting, officially called the eighth session of the conference of the parties to the Climate Change Convention, is due to end on 31 October.