title: Warming caused by cumulative carbon emissions towards the trillionth tonne.
abstract: Global efforts to mitigate climate change are guided by projections of future temperatures. But the eventual equilibrium global mean temperature associated with a given stabilization level of atmospheric greenhouse gas concentrations remains uncertain, complicating the setting of stabilization targets to avoid potentially dangerous levels of global warming. Similar problems apply to the carbon cycle: observations currently provide only a weak constraint on the response to future emissions. Here we use ensemble simulations of simple climate-carbon-cycle models constrained by observations and projections from more comprehensive models to simulate the temperature response to a broad range of carbon dioxide emission pathways. We find that the peak warming caused by a given cumulative carbon dioxide emission is better constrained than the warming response to a stabilization scenario. Furthermore, the relationship between cumulative emissions and peak warming is remarkably insensitive to the emission pathway (timing of emissions or peak emission rate). Hence policy targets based on limiting cumulative emissions of carbon dioxide are likely to be more robust to scientific uncertainty than emission-rate or concentration targets. Total anthropogenic emissions of one trillion tonnes of carbon (3.67 trillion tonnes of CO(2)), about half of which has already been emitted since industrialization began, results in a most likely peak carbon-dioxide-induced warming of 2 degrees C above pre-industrial temperatures, with a 5-95% confidence interval of 1.3-3.9 degrees C.
authors.affiliation: Department of Physics, University of Oxford, OX1 3PU, UK. myles.allen@physics.ox.ac.uk
authors.forename: Myles R
authors.initials: MR
authors.lastname: Allen
authors.forename: David J
authors.initials: DJ
authors.lastname: Frame
authors.forename: Chris
authors.initials: C
authors.lastname: Huntingford
authors.forename: Chris D
authors.initials: CD
authors.lastname: Jones
authors.forename: Jason A
authors.initials: JA
authors.lastname: Lowe
authors.forename: Malte
authors.initials: M
authors.lastname: Meinshausen
authors.forename: Nicolai
authors.initials: N
authors.lastname: Meinshausen
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D019985:Benchmarking; D002244:Carbon / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis*; D003198:Computer Simulation; D017752:Greenhouse Effect; D049671:History, 18th Century; D049672:History, 19th Century; D049673:History, 20th Century; D049674:History, 21st Century; D006802:Human Activities / Q000266:history; D007221:Industry / Q000266:history; D008962:Models, Theoretical; D013696:Temperature; D013997:Time Factors; D035501:Uncertainty
chemical_list: D002245:Carbon Dioxide; D002244:Carbon