Humanity has now entered a new climate reality era, with carbon dioxide concentrations expected to remain above the level of 400 parts per million throughout 2016 and for many generations to come, the World Meteorological Organization says.

The WMO, the United Nations system’s leading agency on weather, climate and water, says the globally averaged concentration of carbon dioxide in the atmosphere reached “the symbolic and significant milestone of 400 parts per million“ for the first time in 2015 and surged again to new records in 2016 on the back of the very powerful El Niño event.

CO₂ levels reached the 400 ppm barrier for certain months during 2015 and in certain places, but they have never done so on a global average basis for the entire year. The WMO says in its annual Greenhouse Gas Bulletin that the growth spurt in CO₂ was fuelled by El Niño, which started in 2015 and had a strong impact well into this year.

This, it says, triggered droughts in tropical regions and reduced the capacity of ‘sinks’ like forests, vegetation and the oceans to absorb CO_2. These sinks currently absorb about half of CO₂ emissions, but there is a risk that they could become saturated, increasing the proportion of carbon dioxide which stays in the atmosphere.

A 37% increase in ‘radiative forcing’ in 25 years

Between 1990 and 2015, the Bulletin says, there was a 37% increase in radiative forcing – the warming effect on the climate – because of long-lived greenhouse gases such as carbon dioxide, methane and nitrous oxide (N₂O) from industrial, agricultural and domestic activities.

“The year 2015 ushered in a new era of optimism and climate action with the Paris climate change agreement. But it will also make history as marking a new era of climate change reality with record high greenhouse gas concentrations”, said WMO secretary-general Petteri Taalas. “The El Niño event has disappeared. Climate change has not.”

“The real elephant in the room is carbon dioxide, which remains in the atmosphere for thousands of years and in the oceans for even longer. Without tackling CO₂ emissions, we cannot tackle climate change and keep temperature increases to below 2°C above the pre-industrial era.

“It is therefore of the utmost importance that the Paris Agreement does indeed enter into force well ahead of schedule on 4 November and that we fast-track its implementation.”

The WMO Bulletin also addresses the problem of rising concentrations of methane, the second most important long-lived greenhouse gas, which contributes about 17% of radiative forcing. About 40% of methane is emitted into the atmosphere by natural sources like wetlands and termites, with the rest coming from human activities like cattle breeding, rice growing, fossil fuel exploitation, landfills and biomass burning.

Atmospheric methane reached a new high of about 1,845 parts per billion (ppb) in 2015 and is now 256% of its pre-industrial level. Nitrous oxide’s atmospheric concentration in 2015 was about 328 parts per billion, 121% of pre-industrial levels. 

A ‘scientific base’ for UNFCCC’s Marrakech meeting next month

The Greenhouse Gas Bulletin provides a scientific base for decision-making, and the WMO has released it ahead of the UN climate change negotiations to be held in the Moroccan city of Marrakech from 7-18 November. They will be seeking to translate the Agreenent into an effective way of coping with the new climate reality era the WMO has identified.

The Bulletin says the pre-industrial level of about 278 ppm of CO₂ represented a balance between the atmosphere, the oceans and the biosphere. Human activities, such as the burning of fossil fuels, have altered the natural balance and in 2015 globally averaged levels were 144% of pre-industrial levels. The increase of  CO₂ from 2014 to 2015 was larger than the previous year and the average over the previous 10 years.

The Bulletin says the last El Niño, as well as reducing the capacity of vegetation to absorb CO₂, led to an increase in CO₂ emissions from forest fires. According to the Global Fire Emissions Database, CO₂ emissions in equatorial Asia – where there were serious forest fires in Indonesia in August-September 2015 – were more than twice as high as the 1997-2015 average.

Drought also has a big impact on CO₂ absorption by vegetation,  and scientists saw similar effects during the 1997-98 El Niño.

Alex Kirby writes for Climate News Network, where this article was originally published (CC BY-ND).