The average concentration of CO2 in the atmosphere hit the symbolic level of 400 parts per million (ppm) for the first time in 2015 and has continued to surge in 2016, according to the World Meteorological Organization.
The WMO published its annual Greenhouse Gas Bulletin on Monday. In a news release accompanying the bulletin, the body stated that while CO2 levels had "previously reached the 400ppm barrier for certain months of the year and in certain locations" this had never happened "on a global average basis for the entire year."
The "growth spurt" in CO2 had been fuelled by the global weather phenomenon El Niño, which began in 2015 and had a forceful impact "well into 2016" the WMO said.
Tropical regions had suffered from droughts as a consequence of El Niño, with a reduction in the ability of oceans, forests and vegetation absorb CO2 a further development.
The WMO added that in the 25 years between 1990 and 2015, radiative forcing – which refers to the "warming effect on our climate" – had increased by 37 percent. This was down to long-lived greenhouse gases like carbon dioxide, methane and nitrous oxide from agricultural, industrial and domestic practices.
"The year 2015 ushered in a new era of optimism and climate action with the Paris climate change agreement," Petteri Taalas, secretary-general of the WMO, said in a statement. "But it will also make history as marking a new era of climate change reality with record high greenhouse gas concentrations," Taalas added. "The El Niño event has disappeared. Climate change has not."
The Paris Agreement last December saw global leaders reach an agreement to make sure global warming stayed "well below" 2 degrees Celsius and to "pursue efforts" to limit the temperature rise to 1.5 degrees Celsius.
Taalas went on to describe CO2 as being an elephant in the room, noting that it remained in the atmosphere for thousands of years and in 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," he said.
"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."