GLASGOW, Scotland — The head of the United Nations warned leaders at the global climate summit in Glasgow that “we are digging our own graves” by burning fossil fuels and destroying the environment.

U.N. Secretary-General Antonio Guterres said at the ceremonial opening of the two-week talks Monday that believing recent announcements by governments could turn the tide on climate change were “an illusion,” not least because there are serious questions many countries’ pledges.

“As we open this much anticipated climate conference, we are still heading for climate disaster,” he said.

Guterres urged major economic powers, including emerging nations like China, to “go the extra mile” because they contribute the lion’s share of global greenhouse gas emissions.

He also criticized a confusion over emissions reductions targets, and announced the creation of a new group of experts to propose “clear standards” for measuring commitments from businesses and other non-state actors.