US President Barack Obama is expected to stress a new cooperative approach when he makes his maiden speech in front of the UN today.Obama’s star power all but assures him of a warm welcome. However, the General Assembly’s audience will remind him of past and future difficulties. Iranian President Mahmoud Ahmadinejad and Libya’s Colonel Gaddafi are among other leaders due to address the gathering. The global challenges facing leaders will not be easy, ranging from the environment, nuclear non-proliferation, security and economic growth. Yesterday, China, the world’s biggest carbon emitter, laid out a plan to curb emissions by 2020 at a special UN conference, but consensus among many nations on the best way forward is still missing. Tougher global safeguards against nuclear proliferation remain a top priority. Iran is due to hold direct talks next month with the US and other powers concerned about its nuclear ambitions. Washington will also be keen to press North Korea to return to the suspended six-party talks on its atomic programme.