The head of the United Nations is calling for "immediate, rapid and large-scale" cuts in greenhouse gas emissions to curb global warming.

Antonio Guterres warned governments ahead of next week's annual U.N. General Assembly that climate change is proceeding faster than predicted, and fossil fuel emissions have already bounced back from a pandemic dip.

Speaking at the launch of a U.N.-backed report summarizing current efforts to tackle climate change, Guterres said recent extreme weather showed no country is safe from climate-related disasters.

"These changes are just the beginning of worse to come," Guterres said, according to The Associated Press. "Unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, we will be unable to limit global heating to 1.5 degrees Celsius (2.7 Fahrenheit). The consequences will be catastrophic."

Climate scientist Michael Mann of Pennsylvania State University said the report's warnings ignore strong pledges and important progress already made.

In particular, the 1.5C threshold agreed in Paris didn't apply to individual years, some of which can be unusually hot due to other factors, he said.

"This misleading framing unnecessarily feeds the fears that the public has that we've somehow already crossed that threshold and that it is too late now to prevent," Mann said. "We have not. And it is not."