United Nations Secretary-General Antonio Guterres. (Photo: TED/AFP)

The UN chief made the announcement at a Paris Peace Forum session. Five years after the Paris Agreement on climate change, "we are still not on a trajectory that would enable us to limit the rise in global temperature to 1.5 degrees Celsius," the secretary-general said.

"To do that -- and the scientific community keeps reminding us of this -- we must at all costs reduce greenhouse gas emissions by 45 percent by 2030 and reach carbon neutrality by 2050," he added. To realize the goal, "every country, city, financial institution and company should adopt plans for transitioning to net-zero emissions by 2050," he said.

By early 2021, countries representing more than 65 percent of global carbon dioxide emissions and more than 70 percent of the world economy would have made ambitious commitments to carbon neutrality, he added.