New York: One by one they walked through the front doors of the grand United Nations headquarters: leaders of micro-states and superpowers alike, flanked by teams of advisers and translators.

The global diplomatic community descends on this patch of midtown Manhattan for the annual UN General Assembly like seagulls on a hot chip. Hotels book out; the streets go into lockdown.

This year's event began with a special climate change summit designed to showcase what countries around the world are doing to reduce their carbon emissions. With the world's media watching, most leaders were keen to spruik their progress.

Prime Minister Scott Morrison is shown "smart" McDonald's Drive-Thru technology at 1871, a non-profit digital start-up incubator. Credit:Alex Ellinghausen

New Zealand PM Jacinda Ardern was there on stage. So were Germany's Angela Merkel and France's Emmanuel Macron and British leader Boris Johnson. US President Donald Trump – who has announced his intention to withdraw the US from the Paris climate accords – didn't have a speaking slot but made a surprise appearance in the crowd.