Even if carbon dioxide levels stopped rising today, the world would still warm by 1.6 °C above pre-industrial levels –which is more than three-quarters of the way to the 2 °C limit the world is supposed to be aiming for. That is the implication of two sets of figures announced on Monday.

Global average levels of carbon dioxide in the atmosphere temporarily broke the 400 parts per million level earlier this year for the first time, the World Meteorological Organization said.

Meanwhile, the UK Met Office confirmed what New Scientist reported first in July – that the world has now warmed by 1 °C relative to pre-industrial times.


Climate models show that even if CO 2 levels stopped rising, the world would still warm by around 0.6 °C. So the latest figures mean that even if the world slashed emissions by 60 per cent immediately, which is what it would take to stabilise CO 2 levels, we would still hit 1.6 °C.

Climate scientist Gavin Schmidt of NASA points out that if emissions stopped altogether, CO 2 levels would soon fall. “That would lead to a smaller eventual temperature rise,” he says.

‘Tis the season

Unfortunately, even if countries stick to what they are proposing to do as part of the global climate treaty now being negotiated, emissions and CO 2 levels will continue to climb well past 2030. It therefore appears unlikely that warming can be limited to 2 °C.

CO 2 levels vary from place to place and with the seasons, depending on the balance between plants taking up CO 2 as they grow and releasing it as they decay.

CO 2 levels above 400 parts per million were first recorded in 2012 in a few places. In 2013, the Mauna Loa Observatory in Hawaii, which has been monitoring CO 2 since 1956, recorded levels above 400 parts per million for the first time.

Now the monthly global average has passed 400 parts per million. Because the global average rises and falls by several parts per million every year, this is temporary – it will drop again this year, but next year it will rise even higher. Soon it will remain permanently above 400 parts per million.

Last year the global annual – rather than monthly – average was 398 parts per million. Because CO 2 levels tend to jump extra high in El Niño years – because of events such as the fires in Indonesia – it may pass 400 parts per million as early as this year.

Read more: “Climate downgrade: Human emissions”

Image credit: NOAA