Jiping Liu1, Mirong Song2, Radley M. Horton3, and Yongyun Hu4
Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, NY 12222;
State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,China;
Center for Climate Systems Research, Columbia University, New York, NY 10025;
Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China
This paper addresses the specter of a September ice-free Arctic in the 21st century using newly available simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). We find that large spread in the projected timing of the September ice-free Arctic in 30 CMIP5 models is associated at least as much with different atmospheric model components as with initial conditions. Here we reduce the spread in the timing of an ice-free state using two different approaches for the 30 CMIP5 models: (i) model selection based on the ability to reproduce the observed sea ice climatology and variability since 1979 and (ii) constrained estimation based on the strong and persistent relationship between present and future sea ice conditions. Results from the two approaches show good agreement. Under a high-emission scenario both approaches project that September ice extent will drop to ∼1.7 million km2 in the mid 2040s and reach the ice-free state (defined as 1 million km2) in 2054–2058. Under a medium-mitigation scenario, both approaches project a decrease to ∼1.7 million km2 in the early 2060s, followed by a leveling off in the ice extent (see attached Figure below).
The paper is highlighted by Nature, 2013, 499, 383.
Citation:Liu, J., M. Song, R. M. Horton, and Y. Hu, 2013: Reducing spread in climate model projections of a September ice-free Arctic. PNAS, doi/10.1073/pnas.1219716110.
Figure caption: The evolution of the correlation (blue lines) and constrained estimation of September sea ice extent (red lines) based on the relationship between the simulated September sea ice extent averaged for 2007-2011 and the projected September sea ice extent averaged for the 5-y sliding windows under the (A) RCP4.5 and (B) RCP8.5.
