Poznan, Poland - With talks on global warming stalled, the world's eyes are on Barack Obama to break the impasse after he takes over as US president.
In some ways, it's easy. Under President George W Bush, the United States was vilified for its stand on climate change. Obama has promised US leadership in the complex global give-and-take, so he'll be widely welcomed as the anti-Bush.
Winning US congressional approval for his plans will be the crucial challenge.
Even before that, an activist president in the White House - Obama arrives there on January 20 - means other rich countries will face pressure to join in the solution.