Several key world leaders, including US President Donald Trump, are not taking part in a special UN "climate action" summit that has opened in New York. UN Secretary-General António Guterres said countries could only speak at the summit if they came with action plans to reduce carbon emissions. Brazil and Saudi Arabia are also among the countries staying away.

The summit comes days after several million people took part in a global climate strike led by youth activists. Some of those campaigners, including Swedish teenager Greta Thunberg, will address delegates.

Ahead of the one-day summit, scientists warned that the signs and impacts of global warming were speeding up. The World Meteorological Organization (WMO) said the amount of carbon dioxide going into the atmosphere between 2015 and 2019 had grown by 20% compared with the previous five years.

Opening the summit on Monday, Mr Guterres - who organised the meeting - said the world was "in a deep climate hole" and that urgent action was needed. "Time is running out, but it's not too late," he said. Mr Guterres earlier said he expected "a number of meaningful plans on dramatically reducing emissions during the next decade, and on reaching carbon neutrality by 2050" would be unveiled at the summit.