A New Reconstruction of Arctic Sea Ice Extent Since 1850

Over the last decade, there have been several attempts to reconstruct Arctic Sea Ice Extent. Kinnard et al 2011[1] reconstructed Arctic sea ice over the last 1450 years. Within that paper he also included a reconstruction beginning in 1870. Both of his reconstructions show natural variability of sea ice cover followed by a dramatic decline following ~1970. Walsh et al 2017[2] reconstructed sea ice extent beginning in 1850 with a monthly time resolution. His reconstruction also showed some natural variability followed by a dramatic decrease in sea ice extent following ~1970. But just last year, Brennan et al. 2020[3] examined Walsh’s study and found that likely underestimated sea ice variability, especially in the early 20th century, and sea ice extent is likely more sensitive to rising temperatures than is shown in Walsh’s study. Her analysis produced what is likely the best reconstruction of annual sea ice extent to date, and while it largely agrees with Walsh, it shows a greater decrease in sea ice extent in the early 20th century.

Brennan compares early 20th century warming (ETCW) from 1900-1940 to the satellite era from 1979-2018 by examining average 25-year trends of sea ice extent (SIE). She concludes, “The average reconstructed 25-year trends of SIE indicate that the rate of sea-ice loss during the ETCW was about ∼33–38% smaller than the 25-year trends observed during the satellite era.” Arctic SIE actually started to decrease in the late 1960s, this is the longest decline in SIE occurring at greater rates than has been observed in the in the last 170 years. This is also consistent with Kinnard’s study showing that recent declines in SIE is unprecedented over the last 1450 years.

References:

[1] Kinnard, C., Zdanowicz, C., Fisher, D. et al. Reconstructed changes in Arctic sea ice over the past 1,450 years. Nature 479, 509–512 (2011). https://doi.org/10.1038/nature10581
https://www.researchgate.net/publication/51825483_Reconstructed_changes_in_Arctic_sea_ice_over_the_past_1450_years

[2] Walsh, J.E., Fetterer, F., Scott Stewart, J. and Chapman, W.L. (2017), A database for depicting Arctic sea ice variations back to 1850. Geogr Rev, 107: 89-107. https://doi.org/10.1111/j.1931-0846.2016.12195.x

[3] Brennan, M. K., Hakim, G. J., & Blanchard‐Wrigglesworth, E. (2020). Arctic sea‐ice variability during the instrumental era. Geophysical Research Letters, 47, e2019GL086843. https://doi.org/10.1029/2019GL086843
https://atmos.uw.edu/~mkb22/files/Brennan_etal_2020.pdf

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