Differences between carbon budget estimates unravelled

Rogelj, J. ORCID: https://orcid.org/0000-0003-2056-9061, Schaefer, M., Friedlingstein, P., Gillett, N., van Vuuren, D., Riahi, K. ORCID: https://orcid.org/0000-0001-7193-3498, Allen, M., & Knutti, R. (2016). Differences between carbon budget estimates unravelled. Nature Climate Change 6 (3) 245-252. 10.1038/nclimate2868.

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Abstract

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.

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