The concentration of CO2, which causes global warming, in the Earth's atmosphere increased at a record rate last year to reach a level not seen for more than three million years, the World Meteorological Organisation (WMO) has reported.
This occurred due to the combination of human activity and an El Niño climate effect in the southern hemisphere associated with warmer temperatures during 2016, according to the UN body.
Their latest report has raised alarm among scientists, who warned that the Paris Accord on reducing greenhouse gases (GHGs) is likely to be insufficient to curb temperature increases due to global warming.
It has prompted calls for signatory countries to consider more drastic emissions reductions at upcoming climate negotiations in Bonn during November.
“Globally averaged concentrations of CO2 reached 403.3 parts per million (ppm) in 2016, up from 400.00 ppm in 2015 because of a combination of human activities and a strong El Niño event,” according to the GHG Bulletin, the UN weather agency’s annual report.
This acceleration occurred despite a slowdown – and perhaps even a plateauing – of emissions because El Niño intensified droughts and weakened the ability of vegetation to absorb CO2. As the planet warms, El Niños are expected to become more frequent.
The increase of 3.3 parts per million (ppm) is considerably higher than both the 2.3 ppm rise of the previous 12 months and the average annual increase over the past decade of 2.08 ppm. It is also well above the previous big El Niño year of 1998, when the rise was 2.7 ppm.
The study, which uses monitoring ships, aircraft and on land stations to track emissions, found CO2 in the atmosphere is now increasing 100 times faster than at the end of the last Ice Age due to population growth, intensive agriculture, deforestation and industrialisation.
"Without rapid cuts in CO2 and other GHG emissions, we will be heading for dangerous temperature increases by the end of this century, well above the target set by the Paris climate change agreement," WMO chief Petteri Taalas said.
The momentum from the Paris accord of 2015 is faltering due to the failure of governments to live up to their promises. In a report to be released on Tuesday, UN Environment will show the gap between international goals and domestic commitments leaves the world on course for warming well beyond the 2 degree target and probably beyond 3 degrees. International efforts to act have also been weakened by US president Donald Trump’s decision to quit the accord.
Professor of carbon management at the University of Edinburgh Dave Reay said: “This should set alarm bells ringing in the corridors of power. We know that, as climate change intensifies, the ability of the land and oceans to mop up our carbon emissions will weaken.”
There was still time to steer these emissions down, he added, “and so keep some control, but if we wait too long humankind will become a passenger on a one-way street to dangerous climate change”.
Prof Richard Betts, head of climate impacts research at the Met Office, said: "This verifies the first ever formal forecast of an annual CO2 rise, that we issued in early 2016. We predicted the record rise in CO2 in 2016 before it happened, using the Met Office's seasonal forecast of sea surface temperatures combined with a statistical relationship with the annual CO2 rise, along with data on emissions of CO2 from burning fossil fuels and deforestation."
The WMO predicted 2017 will again break records for concentrations of CO2 and methane, but the growth rate will not be as fast because there is no El Niño effect.
(Additional reporting - Guardian)