A host of world leaders were gathering at the United Nations Headquarters in New York on Monday for the General Assembly's 70th annual General Debate.Issues such as the refugee crisis, terrorism and dealing with the threat of the Islamic State were expected to take center stage, together with climate change and sustainable development.Tweets by @mawilner Monday will see speakers such as US President Barack Obama, Jordan's King Abdullah, Russian President Vladimir Putin and Iranian President Hassan Rouhani.Prime Minister Benjamin Netanyahu will address the General Assembly on Thursday, a day after Palestinian Authority President Mahmoud Abbas.Abbas has promised to drop a "bombshell" in his speech to the UN, refusing to give further details.Tackling climate change is one of the major objectives of the ambitious 2030 Agenda for Sustainable Development which the Assembly adopted on Friday. Composed of 17 goals and 169 targets, the Agenda is an essential plank in the effort to wipe out poverty, fight inequality and enhance medical and educational access over the next 15 years. Unchecked climate change could undermine all the other goals.Ahead of this 70th anniversary General Debate, Mr. Ban will present his annual report on the work of the Organization. This year's Assembly President, Mogens Lykketoft of Denmark, will then deliver the keynote opening speech. He will then be followed by Brazilian President Dilma Rousseff, whose country holds the traditional role of first national speaker. She will be followed by Obama as leader of the host nation.