Heat-trapping carbon dioxide gas was measured at 393.1 parts per million last year, up 2.2 ppm from the previous year, said the Geneva-based World Meteorological Organisation in its annual greenhouse gas inventory.

That is far beyond the 350 ppm that some scientists and environmental groups promote as the absolute upper limit for a safe level.

“For all these major greenhouse gases the concentrations are reaching once again record levels,” WMO Secretary-General Michel Jarraud told a news conference.

Worse than ever

He said the accelerating trend was driving climate change, making it harder to keep global warming to within 2C of pre-industrial levels, a target agreed at a Copenhagen summit in 2009.

“This year is worse than last year, 2011. 2011 was worse than 2010,” he said. “Every passing year makes the situation somewhat more difficult to handle, it makes it more challenging to stay under this symbolic two degree global average.”

Greenhouse gas emissions are set to be 8-12 billion tons higher in 2020 than the level needed to keep global warming below 2 degrees, the UN Environment Programme said on Tuesday.

If the world pursues its “business as usual” trajectory, it will probably hit the 2C mark in the middle of the century, Jarraud said, noting that this would also affect the water cycle, sea levels and extreme weather events.

“The more we wait for action, the more difficult it will be to stay under this limit and the more the impact will be for many countries, and therefore the more difficult it will be to adapt.”

Delegates from more than 190 nations meet in Warsaw next week for a UN conference to work on emission cuts under a new climate pact to be signed by 2015, but to come into force only in 2020.

‘Unprecedented’ warming

The WMO bulletin said the volume of carbon dioxide, or CO2, the primary greenhouse gas emitted by human activities, grew faster in 2012 than in the previous decade, reaching 393.1 parts per million (ppm), 41 percent above the pre-industrial level.

The amount of the gas in the atmosphere grew by 2.2 ppm, higher the average of 2.02 ppm over the past 10 years.

Based on that rate, the organisation says the world’s carbon dioxide pollution level is expected to cross the 400 ppm threshold by 2016. That level already was reached at some individual measurement stations in 2012 and 2013.

Carbon dioxide is very stable and is likely to remain in the atmosphere for a long time, Jarraud said. The concentrations were the highest for more than 800,000 years, he said.

“The increase in CO2 is mostly due to human activities,” Jarraud said. “The actions we take now or don’t take now will have consequences for a very, very long period.”