Agence France Presse: A global agreement on tackling climate change will be much more likely under a new US president, top US investment bank Lehman Brothers said here Thursday. US leadership is key to reaching a deal to cut greenhouse gas emissions, it said, noting that all White House challengers are talking up the need to tackle the issue. Americans go to the polls in November to elect a new president to succeed President George W. Bush, whose Republican administration has refused to ratify the …