Differences between carbon budget estimates unravelled

Several methods exist to estimate the cumulative carbon emissions that would keep global warming to below a given temperature limit. Here we review estimates reported by the IPCC and the recent literature, and discuss the reasons underlying their differences. The most scientifically robust number — the carbon budget for CO2-induced warming only — is also the least relevant for real-world policy. Including all greenhouse gases and using methods based on scenarios that avoid instead of exceed a given temperature limit results in lower carbon budgets.

To limit warming below the internationally agreed temperature limit of 2 °C relative to pre-industrial levels with >66% chance, the most appropriate carbon budget estimate is 590–1,240 GtCO2 from 2015 onwards.

Variations within this range depend on the probability of staying below 2 °C and on end-of-century non-CO2 warming. Current CO2 emissions are about 40 GtCO2 yr–1, and global CO2 emissions thus have to be reduced urgently to keep within a 2 °C-compatible budget.

Authors

Joeri Rogelj, Michiel Schaeffer, Pierre Friedlingstein, Nathan P. Gillett, Detlef P. van Vuuren, Keywan Riahi, Myles Allen, Reto Knutti

Specifications

Publication title
Differences between carbon budget estimates unravelled
Publication date
24 February 2016
Publication type
Publication
Magazine
Nature Climate Change
Product number
2384