|Title||Differences between carbon budget estimates unravelled|
|Author(s)||Rogelj, Joeri; Schaeffer, Michiel; Friedlingstein, Pierre; Gillett, Nathan P.; Vuuren, Detlef P. Van; Riahi, Keywan; Allen, Myles; Knutti, Reto|
|Source||Nature Climate Change 6 (2016). - ISSN 1758-678X - p. 245 - 252.|
|Department(s)||Environmental Systems Analysis Group|
|Publication type||Refereed Article in a scientific journal|
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. For a >66% chance of limiting warming below the internationally agreed temperature limit of 2 °C relative to pre-industrial levels, 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.