Geneva: Concentrations of carbon dioxide and other greenhouse gases in the atmosphere hit a new high in 2014, the UN said today, warning the resulting climate change was moving the world into "unchartered territory".
In its annual report on Earth-warming greenhouse gases in the atmosphere, the World Meteorological Organization said concentrations of carbon dioxide (CO2), methane and nitrous oxide once again broke records last year.
"We are moving into unchartered territory at a frightening speed," WMO chief Michel Jarraud said in a statement.
The report came as country envoys Monday gathered in Paris to iron out tough political questions ahead of a key summit tasked with sealing a climate rescue pact.
"Every year we report a new record in greenhouse gas concentrations," Jarraud said.
"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," he warned.
His appeal comes just weeks before a Paris summit aimed at ensuring global warming is limited to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels.
Jarraud said that CO2, by far the main culprit in global warming, can remain in the atmosphere for hundreds of years and in the ocean even longer.
"Past, present and future emissions will have a cumulative impact on both global warming and ocean acidification," he said, stressing "the laws of physics are non-negotiable."
WMO's report, which does not measure emissions of greenhouse gases but rather their concentrations in the atmosphere, showed that CO2 had risen to 397.7 parts per million (ppm) in the atmosphere last year.
That was 143 per cent of levels prior to the year 1750, WMO said, adding that CO2 concentrations would likely pass the ominous 400-ppm threshold in 2016.
"We will soon be living with globally averaged CO2 levels above 400 parts per million as a permanent reality," Jarraud said.
"We can't see CO2. It is an invisible threat, but a very real one," he said.
"It means hotter global temperatures, more extreme weather events like heatwaves and floods, melting ice, rising sea levels and increased acidity of the oceans," he said.
Oceans swallow about a quarter of greenhouse gas emissions, while the biosphere sucks up another quarter.