CO2 levels 'increased at record-breaking speed in 2016'
The World Meteorological Organisation says rapid cuts to greenhouse gases are needed.
Carbon dioxide concentrations in the atmosphere increased at record-breaking speed last year, the UN weather agency has warned.
The World Meteorological Organisation said rapid cuts to CO2 and other greenhouse gases are needed to avoid "dangerous temperature increases" by 2100 that would far surpass targets set in the Paris climate accord.
WMO secretary-general Petteri Taalas said: "We are actually moving in the wrong direction."
He added: "Without rapid cuts in CO2 and other greenhouse gas emissions, we will be heading for dangerous temperature increases by the end of this century, well above the target set by the Paris climate change agreement."
The latest WMO Greenhouse Gas Bulletin said a strong El Nino and human activity contributed to an increase of CO2 concentrations to 403.3 parts per million last year, up from 400 in 2015.
The Greenhouse Gas Bulletin, the UN weather agency's annual flagship report, read: "Globally averaged concentrations of CO2 reached 403.3 parts per million (ppm) in 2016, up from 400.00 ppm in 2015 because of a combination of human activities and a strong El Niño event."
The WMO said the report breaks ground by showing the "global picture" on carbon levels.
It hopes that will contribute to debate at a major climate conference in Bonn, Germany, starting next week.