Atmospheric levels of CO2 pass symbolic threshold of 400ppm
Carbon dioxide (CO²) in the Earth’s atmosphere passed 400 parts per million (ppm) on average in 2015 for the first time, prompting scientists to declare that the world is in a new era of “climate change reality”.
The 400ppm figure, which was revealed in the World Meteorological Organisation’s (WMO) annual greenhouse gas bulletin, has been described as a symbolic threshold that will not fall for many generations.
The longest established greenhouse gas monitoring station in the world, in Mauna Loa in Hawaii, predicts CO² concentrations will stay above the symbolic 400ppm for the whole of 2016 and reach new highs.
The findings bolster similar conclusions reached in the latest State Of The Climate report which was released in August and showed that dozens of climate records were broken last year.
The growth spurt in CO² levels, which saw a bigger-than-average increase in the greenhouse gas in the atmosphere between 2014 and 2015, was fuelled by the El Nino weather phenomenon in the Pacific.
The strong El Nino, which started in 2015 and continued into this year, triggered droughts in tropical regions and reduced the ability of forests, vegetation and oceans to absorb CO², leaving more in the atmosphere.
Yet over the longer term it is the increase of greenhouse gases such as CO², methane and nitrous oxide from human activity, including industry and agriculture, which caused a 37 per cent increase in the warming effect on the planet between 1990 and 2015.
Around two-thirds of the warming effect, known as radiative forcing by long-lived greenhouse gases, comes from CO².
Levels of CO² in the atmosphere stood at around 278ppm before the Industrial Revolution, a concentration which the WMO said represented a natural balance on Earth.
However, human activities have altered the natural balance and global average levels of CO² have risen to 44 per cent above pre-industrial levels in 2015.
The greenhouse gas bulletin was released ahead of the next round of climate talks, which will mark the early entry into force of the Paris Agreement, the world’s first comprehensive deal to tackle climate change agreed in the French capital last year.
WMO secretary-general Petteri Taalas said: “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.”
He added: “The El Nino event has disappeared. Climate change has not.
“Without tackling carbon dioxide 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 that the Paris Agreement does indeed enter into force well ahead of schedule on November 4 and that we fast-track its implementation.”
The Paris agreement commits countries to keeping temperature rises to “well below” 2°C and to pursue efforts to limit increases to 1.5°C, by cutting greenhouse gas emissions to net zero in the second half of the century.