Concentrations of carbon dioxide and other greenhouse gases in the atmosphere hit a new high in 2014, the UN said Monday, calling for urgent action to rein in climate change.

"Every year we report a new record in greenhouse gas concentrations. Every year we say that the time is running out. We have to act now to slash greenhouse gas emissions if we are to have a chance to keep the increase in temperatures to manageable levels," World Meteorological Organization chief Michel Jarraud said.