title: Predicting future uncertainty constraints on global warming projections.
abstract: Projections of global mean temperature changes (ΔT) in the future are associated with intrinsic uncertainties. Much climate policy discourse has been guided by "current knowledge" of the ΔTs uncertainty, ignoring the likely future reductions of the uncertainty, because a mechanism for predicting these reductions is lacking. By using simulations of Global Climate Models from the Coupled Model Intercomparison Project Phase 5 ensemble as pseudo past and future observations, we estimate how fast and in what way the uncertainties of ΔT can decline when the current observation network of surface air temperature is maintained. At least in the world of pseudo observations under the Representative Concentration Pathways (RCPs), we can drastically reduce more than 50% of the ΔTs uncertainty in the 2040 s by 2029, and more than 60% of the ΔTs uncertainty in the 2090 s by 2049. Under the highest forcing scenario of RCPs, we can predict the true timing of passing the 2 °C (3 °C) warming threshold 20 (30) years in advance with errors less than 10 years. These results demonstrate potential for sequential decision-making strategies to take advantage of future progress in understanding of anthropogenic climate change.
authors.affiliation: Center for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Shiogama
authors.affiliation: Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: D
authors.initials: D
authors.lastname: Stone
authors.affiliation: Center for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Emori
authors.affiliation: Center for Social and Environmental Systems Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Department of Industrial Administration, Faculty of Science and Technology, Tokyo University of Science, Chiba 278-8510, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Mori
authors.affiliation: Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-8902, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Maeda
authors.affiliation: Center for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Ishizaki
authors.affiliation: School of Geography and the Environment, University of Oxford, OX1 3QY, Oxford, UK.|Department of Physics, University of Oxford, OX1 3QY, Oxford, UK.
authors.forename: M R
authors.initials: MR
authors.lastname: Allen