Liu, J. et al., PNAS, 2012 World Weather Open Science Conference, Montreal, Canada, August 17, 2014 Jiping Liu University at Albany, State University of New York Contributors: Mirong Song, Radley Horton, Yongyun Hu, and Chaoyuan Yang Reducing Spread in Climate Model Projections of a September Ice-Free Arctic

IPCC AR4 “… late-summer sea ice is projected to disappear almost completely towards the end of the 21st century under the SRES A2 scenario in some models” (2007) Arctic might be ice-free in Arctic Marine Shipping Assessment report (2009) Wadhams, Duarte, Maslowski, et al. Large uncertainty in the projected timing of the ice-free Arctic in a warming environment!

Land physics and hydrology Ocean ecology, biogeochemistry Atmospheric circulation and radiation Atmospheric chemistry, aerosols Ocean circulation Plant ecology, land use Climate/Earth System Models Sea Ice CMIP5 vs. CMIP3 A more diverse set of model types A number of improvements in physics, numerical algorithms, and configurations A new set of scenarios called Representative Concentration Pathways (RCPs) Interactive CO 2 CMIP5 - Coupled Model Intercomparison Project Phase 5 A coordinated project by climate modeling community An important resource for IPCC AR5, and beyond

~650 ppm CO 2 ~1370 ppm CO 2 RCP4.5: medium-mitigation emission scenario RCP8.5: high-emission scenario

Time-series of simulated September sea ice extent from 1979 to 2100 for 30 CMIP5 models (thick black: observation; thick red: multi-model ensemble mean)

Projected timing of September ice-free Arctic (defined as less than 1 million km2) for 30 CMIP5 models under RCP4.5 (blue bars) and RCP8.5 (red bars) RCP8.5: !

Two different approaches: Model selection (based on the ability to reproduce the observed sea ice climatology and variability since 1979) Constrained estimation (based on the strong and persistent relationship between present and future sea ice conditions)

(a) Climatology and (b) linear trend of September sea ice extent for observations (black bar on left) and each CMIP5 model (gray bars) during % of observed climatology 30% of observed trend

ACCESS1.0, ACCESS1.3, BNU-ESM, CESM1-BGC, CESM1-CAM5, HADGEM2-CC, MIROC5, MIRO-ESM.CHEM, MPI- ESM.MR Time-series of simulated (color lines) September sea ice extent from 1979 to 2100 for 9 selected models Timing of ice-free: 2054

ensemble mean (9 selected models) Obs. when September ice extent is below 1.7 million km 2 (ensemble mean) Sea ice concentration Sea ice thickness

Two different approaches: Model selection (based on the ability to reproduce the observed sea ice climatology and variability since 1979) Constrained estimation (based on strong and persistent relationship between present and future sea ice conditions)

Scatter plot of September sea ice extent in present mean state ( ) versus September sea ice extent in the projected future state ( ) simulated by 30 CMIP5 models (small dots) (big dot: observed present mean state) r=0.93 r=0.95 present state projected state present state projected state

centered on centered on 2097 Evolution of correlation (blue lines) and constrained estimation of September sea ice extent (red lines) based on the relationship between simulated September ice extent averaged for and projected September ice extent averaged for 5-year sliding windows Timing of ice-free: (centered on 2058)

Projected timing for the September ice-free Arctic in CMIP5 models (RCP8.5) Large spread: (original) Reduced spread: ! Increased maritime activities in the Arctic Ocean and substantial climate impacts have been emerging in the Arctic in advance of the ice-free state!

CMIP5: decadal prediction experiments 10-year simulations initialized every 5-year yrs

September sea ice extent (black: observations; thick red: ensemble mean of decadal hindcasts) NCEP CFSv2NASA GEOS-5

Temporal correlation of September sea ice extent anomaly between observation and decadal hindcasts (lead time of 1-year) NCEP CFSv2NASA GEOS-5

NCEP CFSv2NASA GEOS-5 Temporal correlation of September sea ice extent anomaly between observation and decadal hindcasts (lead time of 2-5 year average)

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