Levels of CO2 in the atmosphere have surged past an important threshold and may not dip below it for "many generations". The 400 parts per million benchmark, which was broken globally for the first time in recorded history in 2015, is likely to make 2016 the first full year to exceed the mark, says the World Meteorological Organization (WMO) in its latest report.
The high levels can be partly attributed to a strong El Niño event. While human emissions of CO2 remained fairly static between 2014 and 2015, the onset of a strong El Niño weather phenomenon caused a spike in levels of the gas in the atmosphere.
Drought conditions in tropical regions produced by El Niño meant vegetation in those areas was less able to absorb CO2. There were also extra emissions from fires, sparked by the drier conditions. In their annual Greenhouse Gas Bulletin, the WMO says the drier conditions helped push the growth in the levels of CO2 in the atmosphere above the average for the last ten years.
At the atmospheric monitoring station in Mauna Loa, Hawaii, levels of CO2 broke through 400 parts per million (ppm), meaning 400 molecules of CO2 for every one million molecules in the atmosphere. The last time CO2 was regularly above 400ppm was three to five million years ago, say experts.
Prior to 1800, atmospheric levels were around 280ppm, according to the US National Oceanic And Atmospheric Administration (NOAA). The WMO says that the rise through the 400ppm barrier has persisted and it is likely that 2016 will be the first full year when the measurements show CO2 above that benchmark, and "hence for many generations".
The report also details the growth in other greenhouse gases, including methane and nitrous oxide. In 2015, levels of methane were 2.5 times greater than in the pre-industrial era, while nitrous oxide was 1.2 times above the historic measure.
While welcoming new initiatives like the global agreement to phase out HFC gases agreed recently in Rwanda, the WMO argues that nations must retain their focus on cutting CO2. The organization notes that without tackling CO2 emissions, the world will not be able to tackle climate change and keep temperature increases to below 2 degrees C above the pre-industrial era, as agreed to in the Paris Agreement.
Around 200 nations who signed the Paris climate agreement are set to meet in Morocco in November for the COP22 conference to decide on the next steps forward.