Michel Jarraud made the pronouncement as he presented the World Meteorological Organization’s annual review of the world’s climate.
The report concludes that last year tied with 2007 as the sixth-hottest since reliable records began over 150 years ago.
It also says that 13 of the 14 warmest years on record have occurred in this century.
“The warming of our oceans has accelerated, and at lower depths. More than 90 percent of the excess energy trapped by greenhouse gases is stored in the oceans," Jarraud told a news conference.
“Greenhouse gases are at record levels, meaning that our atmosphere and oceans will continue to warm for centuries to come. The laws of physics are non-negotiable,” Jarraud added.