The US has given perhaps its clearest signal yet that it will countenance signing up to a successor to the international Kyoto Treaty on climate change as negotiations for a post-2012 agreement kicked off in Bali.

The conference began with news that Australia's newly elected prime minister Kevin Rudd had signed documents to ratify the Kyoto Protocol just hours after being officially sworn into office. The move prompted almost a minute's applause from delegates at the Bali conference where representatives from over 180 nations are gathered to agree a roadmap for a new treaty to replace Kyoto when it expires in 2012.

Australia's ratification of the treaty leaves the US as the only industrialised country not to join the Kyoto agreement, which imposes binding targets for countries to cut emissions by at least five per cent on 1990 levels by 2012.

However, according to Reuters reports, the US delegation leader Harlan Watson has signalled that the US is serious about seeking a new global deal to replace Kyoto and will keep an open mind on whether emission reduction targets should be flexible, as president Bush has insisted up to this point, or mandatory, as is the case under the current Kyoto Accord.

"We're not here to be a roadblock," Watson told reporters at the event, adding that the US delegation would work "constructively" to develop a roadmap for the development of a post-Kyoto agreement.

However, he reiterated the US position that any agreement would have to be global and include developing nations such as China and India alongside developed economies.

Watson also maintained that with the current Kyoto framework failing to deliver the expected emission cuts, any successor would have to look significantly different. "The current regime of legally binding is not doing the job," he said. "Only a few countries have reduced emissions absolutely – the UK, Germany and a few others ... It's going to take heroic steps to meet 2012 targets."

However, despite many countries' difficulties in meeting the Kyoto targets, European negotiators have vowed to press hard for a significant tightening of the current framework, including more demanding emission reduction targets, expanded carbon trading, greater co-operation on clean technology development, and the inclusion of emissions from aviation and shipping in any agreement.