Going through the ceiling!

Sometime in the next month, the analyser at Hawai is expected to record a daily concentration of carbon dioxide in the atmosphere of more than 400 parts per million (p.p.m.)At 400 p.p.m., nations will have a difficult time keeping global warming in check, says Corinne Le Quéré, a climate researcher at the University of East Anglia in Norwich, UK, who says that the impact “is getting very dangerously close to reaching the 2 °C target that governments around the world have pledged not to exceed”.

Emissions of other greenhouse gases are also increasing, pushing the total equivalent concentration of CO₂ in the atmosphere to around 478 p.p.m. in April, according to Ronald Prinn, an atmospheric scientist at the Massachusetts Institute of Technology in Cambridge.

Data compiled by Le Quéré and other members of the Global Carbon Project suggest that humans contributed around 10.4 billion tons of carbon into the atmosphere in 2011. About half of that is taken up each year by carbon ‘sinks’ such as the ocean and vegetation on land; the rest remains in the atmosphere and raises the global concentration of CO₂.

The sinks have grown substantially but climate models suggest that the land and ocean will not keep pace for long. Some researchers have suggested that the sinks have already started to clog up, reducing their ability to take up more CO₂ (J. G. Canadell et al. Proc. Natl Acad. Sci. USA 104, 18866–18870; 2007). Others disagree.