Shortly after entering office in 2009, Barack Obama tried to show his commitment to tackling climate change by appointing Dr Steven Chu, a Nobel Prize-winning Chinese-American scientist, as energy secretary.
Clearly any agreement on a global framework hinged on Sino-US relations. In this regard, the year started well, with Hillary Clinton's visit to China in February. She sought to incorporate climate change into talks about trade relations. This effort was reinforced by Todd Stern, the leading US climate-change negotiator, who travelled to Beijing in June to push for China's participation in a successor to the Kyoto Protocol.
However, climate change was pushed down the agenda at the US-China Strategic and Economic Dialogue in July, as each party sought reassurances regarding the other's economic policies. With momentum gathering for the Copenhagen talks, both countries used September's G20 summit and UN General Assembly to stress their commitment to combating climate change.
Expectations of a deal were raised further after Obama's visit to China in November, despite a lack of firm pledges from either side. But in the blame game that followed Copenhagen, Washington and Beijing questioned each other's dedication to finding an answer to climate change.