Nature 458, 1158-1162 (30 April 2009) | doi:10.1038/nature08017; Received 25 September 2008; Accepted 25 March 2009
Greenhouse-gas emission targets for limiting global warming to 2 °C
- Potsdam Institute for Climate Impact Research, Telegraphenberg, 14412 Potsdam, Germany
- Department of Statistics, University of Oxford, South Parks Road, Oxford OX1 3TG, UK
- Climate Analytics, Telegraphenberg, 14412 Potsdam, Germany
- Centre for Air Transport and the Environment, Manchester Metropolitan University, Chester Street, Manchester M1 5GD, UK
- Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland
- Smith School of Enterprise and the Environment, University of Oxford, Oxford OX1 2BQ, UK
- Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK
Correspondence to: Malte Meinshausen1 Correspondence and requests for materials should be addressed to M.M. (Email: ).
More than 100 countries have adopted a global warming limit of 2 °C or below (relative to pre-industrial levels) as a guiding principle for mitigation efforts to reduce climate change risks, impacts and damages1, 2. However, the greenhouse gas (GHG) emissions corresponding to a specified maximum warming are poorly known owing to uncertainties in the carbon cycle and the climate response. Here we provide a comprehensive probabilistic analysis aimed at quantifying GHG emission budgets for the 2000–50 period that would limit warming throughout the twenty-first century to below 2 °C, based on a combination of published distributions of climate system properties and observational constraints. We show that, for the chosen class of emission scenarios, both cumulative emissions up to 2050 and emission levels in 2050 are robust indicators of the probability that twenty-first century warming will not exceed 2 °C relative to pre-industrial temperatures. Limiting cumulative CO2 emissions over 2000–50 to 1,000 Gt CO2 yields a 25% probability of warming exceeding 2 °C—and a limit of 1,440 Gt CO2 yields a 50% probability—given a representative estimate of the distribution of climate system properties. As known 2000–06 CO2 emissions3 were 234 Gt CO2, less than half the proven economically recoverable oil, gas and coal reserves4, 5, 6 can still be emitted up to 2050 to achieve such a goal. Recent G8 Communiqués7 envisage halved global GHG emissions by 2050, for which we estimate a 12–45% probability of exceeding 2 °C—assuming 1990 as emission base year and a range of published climate sensitivity distributions. Emissions levels in 2020 are a less robust indicator, but for the scenarios considered, the probability of exceeding 2 °C rises to 53–87% if global GHG emissions are still more than 25% above 2000 levels in 2020.