The carbon dioxide (CO2) emissions that drive global warming -- flat since 2014 -- are set to rise two percent this year, dashing hopes they had peaked, scientists reported at UN climate talks Monday.

"This is very disappointing," said Corinne Le Quere, director of the Tyndall Centre for Climate Change Research at the University of East Anglia and lead author of a major study detailing the findings.

"With global CO2 emissions from human activities estimated at 41 billion tonnes for 2017, time is running out on our ability to keep warming below two degrees Celsius (3.6 degrees Fahrenheit), let alone 1.5 C