The World Meteorological Organization’s Greenhouse Gas Bulletin says that between 1990 and 2014 there was a 36% increase in radiative forcing – the warming effect on our climate – because of long-lived greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from industrial, agricultural and domestic activities.

The WMO report also highlights the interaction and amplification effect between rising levels of CO2 and water vapour, which is itself a major greenhouse gas, albeit short-lived. Warmer air holds more moisture and so increased surface temperatures caused by CO2 would lead to a rise in global water vapour levels, further adding to the enhanced greenhouse effect. Further increases in CO2 concentrations will lead to disproportionately high increases in thermal energy and warming from water vapour.

“Every year we report a new record in greenhouse gas concentrations,” said WMO Secretary-General Michel Jarraud. “Every year we say that 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.”

Atmospheric concentrations of CO2 – the most important long-lived greenhouse gas – reached 397.7 parts per million (ppm) in 2014. In the Northern hemisphere CO2 concentrations crossed the symbolically significant 400 ppm level in 2014 spring, when CO2 is most abundant. In spring 2015, the global average concentration of CO2 crossed the 400 ppm barrier.

“We will soon be living with globally averaged CO2 levels above 400 parts per million as a permanent reality,” Said Mr Jarraud

“We can’t see CO2. It is an invisible threat, but a very real one. It means hotter global temperatures, more extreme weather events like heatwaves and floods, melting ice, rising sea levels and increased acidity of the oceans. This is happening now and we are moving into uncharted territory at a frightening speed,” he said.

“Excess energy trapped by CO2 and other greenhouse gases is heating up the Earth surface which leads to increase in atmospheric water vapour which in turn is generating/trapping even more heat,” said Mr Jarraud.

“Carbon dioxide remains in the atmosphere for hundreds of years and in the ocean for even longer. Past, present and future emissions will have a cumulative impact on both global warming and ocean acidification. The laws of physics are non-negotiable,” said Mr Jarraud.

The WMO Greenhouse Gas Bulletin reports on atmospheric concentrations – and not emissions - of greenhouse gases. Emissions represent what goes into the atmosphere. Concentrations represent what remains in the atmosphere after the complex system of interactions between the atmosphere, biosphere, cryosphere and the oceans. About a quarter of the total emissions is taken up by the oceans and another quarter by the biosphere, reducing in this way the amount of CO2 in the atmosphere.

The Greenhouse Gas Bulletin provides a scientific base for decision-making. WMO releases it ahead of the U.N. climate change negotiations in Paris, to be held from 30 November to 11 December. A separate Emissions Gap report, from the United Nations Environment Programme, focuses on annual emissions of CO2.

Carbon dioxide (CO2) accounted for about 83% of the total increase in radiative forcing by long-lived greenhouse gases over the past decade. The pre-industrial level of about 278 ppm represented a balance between the atmosphere, the oceans and the biosphere. Human activities such as the burning of fossil fuels has altered the natural balance and in 2014, globally averaged levels were 143% of pre-industrial levels. In 2014, global annual average concentration of CO2 concentrations reached 397.7 ppm with annual increase close to the 10 year averaged. The global annual average is likely to pass 400 ppm in 2016.

Methane CH4 is the second most important long-lived greenhouse gas. Approximately 40% of methane is emitted into the atmosphere by natural sources (e.g., wetlands and termites), and about 60 % comes from human activities like cattle breeding, rice agriculture, fossil fuel exploitation, landfills and biomass burning. Atmospheric methane reached a new high of about 1833 parts per billion (ppb) in 2014 and is now 254% of the pre-industrial level.

Nitrous oxide (N2O) is emitted into the atmosphere from both natural (about 60%) and anthropogenic sources (approximately 40%), including oceans, soil, biomass burning, fertilizer use, and various industrial processes. Its atmospheric concentration in 2014 was about 327.1 parts per billion. This is 121% of pre-industrial levels. It also plays an important role in the destruction of the stratospheric ozone layer which protects us from the harmful ultraviolet rays of the sun.

Water vapour and CO2 are the two major greenhouse gases. But it is CO2 which is the main driver of climate change. Water vapour changes are the so-called feedback mechanisms and happen as a response to the change in CO2. For a scenario considering doubling of is CO2 concentration from pre-industrial conditions, i.e. from about 280 to 560 ppm, water vapour and clouds globally would lead to an increase in atmopsheric warming that is about three times that of long-lived greenhouse gases, according to the Bulletin.