Countries' existing promises regarding emissions reductions are unlikely to prevent global warming exceeding 2 °C above pre-industrial temperatures by the end of the century, meaning that large amounts of carbon may need to be removed from the atmosphere.

Benjamin Sanderson and his co-workers at the US National Center for Atmospheric Research in Boulder, Colorado, explored the odds of staying below 2 °C of warming for a range of emissions pathways. They also analysed whether 'negative emissions' — the removal of carbon from the atmosphere — will be necessary.

To avoid crossing the 2-degree threshold during this century, net global emissions must drop to zero by 2085, the authors find. Depending on the level of near-term reductions, between 1.5 billion and 5 billion tonnes of CO2 per year will need to be captured and removed from the atmosphere thereafter.

Geophys. Res. Lett. http://doi.org/bkqh (2016)