Leipold said the United States' refusal to sign the Kyoto protocol would have disastrous effects on the rest of the world, while domestically it had enthusiastically embraced an "anti-environmental" course.
"The Bush administration is the worst in terms of the environment ever since there was something like environmental policy," he told a press briefing in the Thai capital.
Leipold said the world's increasing consumption of fossil fuels was mostly due to the habits of the western world, particularly the United States which is responsible for one quarter of carbon dioxide emissions.
"It just shows the huge discrepancy between taking advantage of a natural resource, but not taking responsibilty. The US government, President Bush, has clearly said, 'We will not sign the Kyoto protocol because the American way of life is not up for discussion'," he said.
"Well, that's easy for him to say... The consequences however will be first and mostly felt elsewhere," he said, adding that large parts of Bangladesh along with Pacific islands were threatened by an expected rise in sea levels.
"It poses a serious question of justice: Is it fair that the rich exploit a natural resource... and that others pay the cost for it?"
Kyoto is the only international accord that aims at reducing volumes of "greenhouse gas" pollution, the carbon by-product of burning fossil fuels that builds up solar heat in the atmosphere.
Scientists say this is causing Earth's air, land and oceans to warm slowly but steadily.
The protocol's framework was decided in 1997, but it took five years to decide on its complex rulebook.
The agreement was almost destroyed in 2001 after it was abandoned by Bush, who contended it was too costly for the oil-dependent US economy and unfair because it does not bind developing countries to emissions cuts.
Leopold said the high levels of consumption in the developed world were putting severe strain on the global environment.
"It's a very serious question of what level of wealth is affordable worldwide, and I think certainly the US level of wealth and consumption if expanded to the whole world would lead to environmental catastrophe," he said.