If the hottest year ever can’t precipitate ‘ice-free’ conditions in September, what’s it going to take? Arctic sea ice failed to nose-dive again this year, undoubtedly disappointing expects who have been anticipating a ‘death-spiral’ decline for ages. Arctic sea ice hit its seasonal low sometime around mid-September this year and although the precise value hasn’t been published, the average September ice coverage will likely be about 4.2 mkm2 once it gets announced in early October.
This means we have now had 17 years of a near-zero trend for September sea ice, extending the nearly-flat trend NSIDC sea ice experts acknowledged four years ago. This surely busts a huge hole in the prevailing concept that more atmospheric CO2 causes less summer sea ice. Note that CO2 levels measured in August 2023 were 419.7 parts per million (ppm), compared to 382.2 in August 2007, a rise of 37.5ppm with no corresponding decline in summer sea ice (and vs. 314.2 ppm in 1960). Measured in metric tons, CO2 emissions due to fossil fuels rose from 31.1 billion in 2007 to 37.1 billion in 2021 (last year of data), again with no corresponding decline in summer sea ice.
In 2015, Neil Swart and colleagues argued that statistically speaking, the 7-year near-zero trend that was documented from 2007-2013 was caused by natural variability and was eminently compatible with models predicting “ice-free” conditions within decades due to increased CO2 levels. Their models led them to conclude that the possibility of a 14-year near-zero trend (e.g. 2007-2020) was possible but far less likely and that even longer near-zero trends are much more likely to occur when the Arctic is nearly ice-free (i.e. about 1 mkm2).
Surely a near-zero trend lasting 17 years (2007-2023), particularly before extent has reached the scary-sounding “ice-free” level, virtually destroys the assumption that sea ice extent is being controlled by atmospheric CO2 or even global temperatures, especially given the claim that 2023 may be the “hottest year on record”!
You don’t have to be a math wiz to see that there has been a nearly-flat trend in September sea ice extent since 2007 (pink dot marks approximate level for 2023 on this 2022 graph) but Walt Meier at the NSIDC actually did the math back in 2019 (insert), which is now extended another four years.
This absurd idea that atmospheric CO2 controls Arctic sea ice in summer–but causes only a slight decline in winter and no decline in Antarctic sea ice (Blanchard-Wrigglesworth et al. 2022; Crockford 2023)–has been embraced by biologists who want to see polar bears listed as ‘threatened with extinction’ by every government and conservation organization in the world, whatever the cost to their scientific integrity.
Prior to 2015, polar bear specialists needed to inject the IUCN Red List assessment with a semblance of scientific merit, so they programmed their predictive models to assume a linear relationship between CO2 and Arctic sea ice in summer (Notz and Stroeve 2016; Stern and Laidre 2016; Regehr et al. 2016: Wiig et al. 2015). And in 2023, the same assumption was made by Steven Amstrup and his sea ice expert sidekick when they made the ridiculous claim that CO2 emissions can be directly linked to reduced polar bear cub survival across the Arctic (Amstrup and Bitz 2023; Molnar et al. 2020). But while polar bear researchers generally apply this linear CO2-sea ice concept at a regional (subpopulation) scale (and use a slightly different metric of “summer” ice extent), the effect is the same: they assume more global CO2 means that summer sea ice at any Arctic location will continue to decline in a linear fashion decades into the future.
Which brings us back to the pause and my big question: Are polar bear specialists ever going to acknowledge the 17-year near-zero trend in summer sea ice or will they forever just draw a straight line from 1979 and insist summer sea ice is still declining?
As shown below, at 15 September 2023, ice extent was 4.1mkm2 and by September 20, seemed to be on its way back up.
Below, Arctic sea ice extent at 20 September 2023 compared to the previous four years.
Amstrup, S.C. and Bitz, C.M. 2023. Unlock the Endangered Species Act to address GHG emissions. Science 381(6661):949-951. pdf here.
Blanchard-Wrigglesworth, E., I. Eisenman, S. Zhang, et al. 2022. New perspectives on the enigma of expanding Antarctic sea ice, Eos 103. https://doi.org/10.1029/2022EO220076.
Crockford, S.J. 2023. The Polar Wildlife Report. Global Warming Policy Foundation Briefing 63, London. pdf here.
Molnár, P.K., Bitz, C.M., Holland, M.M., Kay, J.E., Penk, S.R. and Amstrup, S.C. 2020. Fasting season length sets temporal limits for global polar bear persistence. Nature Climate Change. https://doi.org/10.1038/s41558-020-0818-9 pdf here.
Notz, D. and Stroeve, J. 2016. Observed Arctic sea-ice loss follows anthropogenic CO2 emission. Science 354(6313):747-750. pdf here.
Stern, H.L. and Laidre, K.L. 2016. Sea-ice indicators of polar bear habitat. Cryosphere 10: 2027-2041.
Swart, N.C., Fyfe, J.C., Hawkins, E., Kay, J.E. and Jahn, A. 2015. Influence of internal variability on Arctic sea-ice trends. Nature Climate Change 5(2): 86–89.
Wiig, Ø., Amstrup, S., Atwood, T., Laidre, K., Lunn, N., Obbard, M., et al. 2015. Ursus maritimus. The IUCN Red List of Threatened Species 2015: e.T22823A14871490. Available from http://www.iucnredlist.org/details/22823/0 [accessed Nov. 28, 2015]. See the supplement for population figures.