According to The Guardian newspaper today (http://www.guardian.co.uk/environment/2009/sep/15/europe-us-copenhagen), in the Draft Implementing Agreement submitted by the US to the UN in May was a clause which stated that emissions reductions will be in accordance with domestic law. It’s clear to see what loopholes this opens up for the unscrupulous!
The problem seems to be one of domestic politics: the urgency of the oncoming crisis appears less appreciated by the US populace and climate change is lower down the list of national priorities than, say, jobs and the national economic interest. The US Senate never ratified the Kyoto Protocol and the Obama administration appears doubtful that a new global treaty would get the 2/3 majority it would need to pass in the Senate, hence the clause. It also appears that there is some conflict between the EU wanting to build on Kyoto and the US desire to sweep Kyoto away and negotiate a new agreement based on their own system.
Critically, this may result in no firm agreement being reached at the UN Climate Change Conference in Copenhagen later this year.
Re-negotiation could take years; years that we may not have. The IPCC report published in May 2007 indicated that global emissions must peak by 2015 in order to prevent a global mean temperature rise of more than 2 degrees Celsius. A 2 degree rise would still affect millions, but a higher rise could be catastrophic (see an interactive map by New Scientist, depicting the projected state of the planet based on a 4 degree rise, here: http://www.newscientist.com/embedded/mg20126971700-surviving-in-a-warmer-world).
While I personally fear that we may be already too late to limit the temperature rise to 2 degrees, we must not despair. We must act! Politicians everywhere must be left in no doubt of the importance, both to us and to our future, of a strong, binding agreement and globally co-ordinated action now.