Extremes become routine in an emerging new Arctic


The Arctic is rapidly warming and experiencing tremendous changes in sea ice, ocean and terrestrial regions. Lack of long-term scientific observations makes it difficult to assess whether Arctic changes statistically represent a ‘new Arctic’ climate. Here we use five Coupled Model Intercomparison Project 5 class Earth system model large ensembles to show how the Arctic is transitioning from a dominantly frozen state and to quantify the nature and timing of an emerging new Arctic climate in sea ice, air temperatures and precipitation phase (rain versus snow). Our results suggest that Arctic climate has already emerged in sea ice. Air temperatures will emerge under the representative concentration pathway 8.5 scenario in the early- to mid-twenty-first century, followed by precipitation-phase changes. Despite differences in mean state and forced response, these models show striking similarities in their anthropogenically forced emergence from internal variability in Arctic sea ice, surface temperatures and precipitation-phase changes.

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Fig. 1: Changes in means and distributions of annual minimum and maximum NH SIE.
Fig. 2: Mean October and February surface temperatures and ToE.
Fig. 3: Relationships among Arctic Ocean SIEs, SIT and October and February polar (70°–90° N) surface air temperature changes, 1980–2099.
Fig. 4: Mean first- and last-rain-day changes and ToE of the rain-season duration.

Data availability

All data used in this study are publicly available. CMIP5-MMLE output are available through the MMLEA (US CLIVAR Multi-Model LE Archive (NCAR); http://www.cesm.ucar.edu/projects/community-projects/MMLEA/). The Walsh extended and NSIDC SICs are available online (https://nsidc.org/).

Code availability

Code to produce all figures is available from the corresponding author.


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We acknowledge support from a grant from the NOAA Climate Program Office Grant NA15OAR4310166 and NSF Grant 1724748. We acknowledge the CESM Large Ensemble Community Project and high-performance computing support from both Yellowstone (ark:/85065/d7wd3xhc) and Cheyenne (https://doi.org/10.5065/D6RX99HX) provided by NCAR’s Computational and Information Systems Laboratory, sponsored by the National Science Foundation. We thank the US National Science Foundation, National Oceanic and Atmospheric Administration, National Aeronautics and Space Administration, and Department of Energy for sponsoring the activities of the US CLIVAR Working Group on Large Ensembles. We also gratefully acknowledge all of the modelling groups listed in Table 1 for making their Large Ensemble simulations available in the Multi-Model Large Ensemble data repository.

Author information




L.L. and M.M.H. conceived the study. L.L. performed the analysis, created the figures and led the writing of the manuscript with contributions from M.M.H.

Corresponding author

Correspondence to Laura Landrum.

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The authors declare no competing interests.

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Peer review information Nature Climate Change thanks John Walsh and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 CMIP5-MMLE NH SIE monthly climatology for 5 decades.

Dashed/dotted lines indicate (1979–1988)/(2010-2019) monthly decadal averages from the NSIDC ice index5. Solid grey line indicates the 1 million km2 ‘Ice Free’ definition.

Extended Data Fig. 2 CMIP5-MMLE and observational based Arctic Sea Ice extents.

Bold solid lines indicate ensemble mean, with opaque polygon showing range of simulations for each ensemble. Extended Sea Ice dataset82 and NSIDC ice index5 are shown in solid dark and light grey, respectively. Insets show PDFs for running 20 yr trends over the 20th Century for each model for both minimum and maximum SIEs.

Extended Data Fig. 3 CMIP5-MMLE Time of Emergence of monthly October and February surface air temperatures.

October/February ToEs are shown in the left/right panels.

Extended Data Fig. 4 CMIP5-MMLE mean October surface air temperature changes from (1950-1959) baseline.

Results shown for early, middle and late 21st century under RCP8.5 forcing scenario. Contours indicate September 15% sea ice concentration contours for base period (1950-1959; black) and future decades (white).

Extended Data Fig. 5 CMIP5-MMLE mean February surface air temperature changes from (1950-1959) baseline.

Results shown for early, middle and late 21st century under RCP8.5 forcing scenario. Contours indicate February 15% and 85% sea ice concentration contours for base period (1950-1959; 15% black) and future decades (15% white, 85% grey).

Extended Data Fig. 6 CMIP5-MMLE first rain day changes from (1950-1959) baseline.

Results shown for early, middle and late 21st century under RCP8.5 forcing scenario.

Extended Data Fig. 7 CMIP5-MMLE last rain day changes from (1950-1959) baseline.

Results shown for early, middle and late 21st century under RCP8.5 forcing scenario.

Extended Data Fig. 8 CMIP5-MMLE rain season duration from (1950-1959) baseline.

Results shown for early, middle and late 21st century under RCP8.5 forcing scenario.

Supplementary information

Supplementary Information

Supplementary Fig. 1, discussion and Table 1.

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Landrum, L., Holland, M.M. Extremes become routine in an emerging new Arctic. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-0892-z

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