Nearly 10 years ago, at the Earth Summit in Rio de Janeiro, world leaders queued up to sign the UN Framework Convention on Climate Change and pledged to take steps to protect the global climate system against dangerous human-induced interference.
The ultimate objective of this convention, which has since been ratified by 186 countries, was to stabilise the build-up of greenhouse gases in the atmosphere so that future generations would not suffer the catastrophic effects of global warming.
All the parties to the 1992 convention accepted as a basic principle that the rich industrialised countries should take the lead in combating climate change. This was only fair as their per capita emissions are between 10 and 20 times higher than those of developing countries.
The convention did not, of course, include specific targets and timetables for reducing emissions of carbon dioxide and other greenhouse gases. That came later, following a tortuous series of negotiations culminating in the adoption of the Kyoto Protocol in December 1997.
Under this treaty, which has been signed by 84 UN member-states and ratified by 35, the industrialised countries are required to reduce their emissions by 5.2 per cent (based on 1990 levels) by 2012 at the latest. Only after that date would developing countries have to make mandatory cuts.
As part of the Kyoto package, the European Union agreed to reduce its overall emissions by 8 per cent, the US by 7 per cent and Japan by 6 per cent. (Ireland, as a relatively under-developed EU member-state, was permitted to increase its emissions by 13 per cent within the overall EU target.)
By any standard, most of all the scientific consensus that cuts of between 60 and 80 per cent in emissions are required to avoid the worst effects of global warming, these targets are modest. But the treaty is widely seen as an essential first step towards deeper cuts in the future.
However, ratification of Kyoto by the major industrialised countries is contingent on reaching agreement on the "rules" under which it would operate. For example, will these countries be able to obtain credits against their own emissions by investing in cleaner technologies elsewhere?
Or will they be allowed to offset their emissions by counting trees as "carbon sinks" or engage in widespread emissions trading - by purchasing what is known as "hot air" from Russia, for example - instead of taking concrete steps to limit carbon dioxide pollution at home?
From the outset, throughout Bill Clinton's presidency, the US sought to make maximum use of such loopholes, fearing that any move away from its fossil fuel economy would have an unacceptable impact on "the American way of life" - based, as it is, on profligate consumption and waste.
The EU does not share this pessimistic view. It believes that the Kyoto targets can be met without damaging economic competitiveness, through such "no regrets" measures as producing more fuel-efficient cars and converting coal- and oilfired power stations to run on natural gas.
It was this clash between the fearful pessimists and the hopeful optimists that collapsed the sixth Conference of the Parties to the Climate Change Convention (COP6) in The Hague.
The current conference in Bonn (COP6.5, as it has become known) is an attempt to pick up the pieces.
In the intervening period, by far the most significant event was the announcement last March that the Bush administration, after just six weeks in office, had decided to walk away from implementing the Kyoto Protocol on the grounds that it was "fatally flawed".
President Bush, whose campaign had been heavily backed by Exxon-Mobil and other fossil fuel interests, even challenged the scientific evidence and branded as "unfair" the current exemption for developing countries such as China and India, whose per capita emissions are fractions of the US figure.
He appeared to have ignored the third assessment report by the UN Intergovernmental Panel on Climate Change, which warned of the dire consequences of taking no action; since then, indeed, the IPCC has said that global temperatures are rising twice as fast as earlier forecasts had indicated.
The reluctance of the US to take part in the Kyoto framework has a lot to do with the fact that its emissions are rising; figures from the UN Climate Convention Database show that they increased by 12.2 per cent in the last decade, compared with less than 1 per cent for the EU.
Other than Australia, which has massive coal reserves, and the oil-producing countries of the Middle East, there is little support for Mr Bush's view that climate change can be tackled on the basis of so far unspecified voluntary measures taken outside the legally binding Kyoto framework.
What campaigning groups such as Greenpeace, Friends of the Earth and the World Wide Fund for Nature are seeking from the Bonn conference is a set of "environmentally sound" rules to implement the Kyoto Protocol in a fair and effective manner, producing measurable cuts in emissions.
In order for the protocol to become international law, it must be ratified by at least 55 UN member-states, including industrialised countries responsible for 55 per cent of greenhouse gas emissions in 1990. And even without US participation, this is still theoretically possible.
That's why so much attention is being paid to Japan, the world's second largest economy. The EU, Japan and Russia account for a third of all emissions from industrialised countries. If they stood together and persuaded others such as Canada and Ukraine to join them, Kyoto would survive.
In that scenario, the moral pressure on the US as the world's largest economy and biggest single emitter of greenhouse gases, could become irresistible. Indeed, that's what US environmental groups, as embarrassed as they are furious with their President's stance, are counting on.
This week's G8 summit in Genoa may prove crucial in edging the process forward, with the leaders of France, Italy, Germany and Britain expected to apply strong pressure on Mr Bush and on the Japanese Prime Minister, Mr Junichiro Koizumi, to permit real progress to be made in Bonn.
It is unlikely, however, that agreement will be reached in Bonn on the rules for implementing Kyoto. In all probability, crucial decisions will be deferred to COP7 in Marrakesh in October.