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According to the World Meteorological Organization or WMO's latest Greenhouse Gas Bulletin, the levels of heat-trapping greenhouse gases in the atmosphere have reached another new record high. 

In 2018, the global average concentrations of CO2 or carbon dioxide reached 407.8 parts per million, up from 405.5 parts per million in 2017. The increase in CO2 from 2017 to 2018 was close to that observed from 2016 to 2017, and it is just above the average over the last 10 years. 

The concentrations of nitrous oxide and methane also surged by higher amounts than during the past 10 years, according to the observations from the Global Atmosphere Watch network that includes stations in the mountain areas, tropical islands, and the remote Arctic.  

Greenhouse gases

Since 1990, there has been a 43% increase in total radiative forcing, which is the warming effect on the climate, by long-lived greenhouse gases. Carbon dioxide accounts for 80% of this, according to the data from the US Nation Oceanic and Atmospheric Administration quoted in the WMO Bulletin. 

According to Petteri Taalas, the WMO Secretary-General, there is no sign of a slowdown in the greenhouse gas concentration in the atmosphere, let alone a decline, despite all the commitments under the Paris Agreement on Climate Change. We need to translate the commitments into action and increase the level of ambition for the sake of the future welfare of mankind. 

Taalas also said that it is worth recalling that the last time the Earth experienced a comparable concentration of carbon dioxide was three to five million years ago.

The Bulletin includes a focus on how isotopes confirm the main role of fossil fuel combustion in the increase of carbon dioxide in the atmosphere. 

Carbon dioxide

The main long-lived greenhouse gas in the atmosphere that is related to human activities is carbon dioxide. Its concentration reached new highs in 2018 of 407.8 ppm, or 147% of pre-industrial levels in 1750. 

The increase in carbon dioxide from 2017 to 2018 was above the average growth rate over the past 10 years. The growth rate of carbon dioxide averaged over three consecutive decades, from 1985 to 1995, 1995 to 2005 and 2005 to 2015. It increased from 1.42 ppm/year to 1.86 ppm/year and to 2.06 ppm/year with the highest annual growth rates observed during El Niño events.


The second most important long-lived greenhouse gas is Methane or CH4. It contributes about 17% of radiative forcing. Around 40% of methane is emitted into the atmosphere by natural sources such as termites and wetlands, and about 60% comes from human activities like rice agriculture, cattle breeding, fossil fuel exploitation, biomass burning, and landfills. 

Atmospheric methane reached a new high of about 1869 parts per billion or ppb in 2018. Atmospheric methane is now 259% of the pre-industrial level. For CH4, the increase from 2017 to 2018 was higher than both that observed from 2016 to 2017 and the average over the last 10 years. 

Nitrous oxide

Nitrous oxide or N2O is emitted into the atmosphere from both natural and anthropogenic sources. Around 60% of the N2O that is emitted into the atmosphere is from natural sources, while 40% is from anthropogenic sources, including soil, oceans, fertilizer use, biomass burning, and various industrial processes. 

Its atmospheric concentration was 331.1 parts per billion in 2018. This is 123% of pre-industrial levels. The increase from 2017 to 2018 was higher than that observed from 2016 to 2017, and the average growth rate over the last decade. 

A new UNEP or UN Environment Programme report released last week warns that unless global greenhouse gas emissions fall by 7.6% each year between 2020 and 2030, the world will miss the opportunity to get on track towards the 1.5°C temperature goal of the Paris Agreement. 

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