Changing State Of Arctic Sea Ice Across All Seasons

[bluewave]

http://iopscience.iop.org/article/10.1088/1748-9326/aade56

TOPICAL REVIEW • THE FOLLOWING ARTICLE IS OPEN ACCESS

Changing state of Arctic sea ice across all seasons

Julienne Stroeve1,2 and Dirk Notz3

Published 24 September 2018 • © 2018 The Author(s). Published by IOP Publishing Ltd
Environmental Research Letters, Volume 13, Number 10

Abstract

The decline in the floating sea ice cover in the Arctic is one of the most striking manifestations of climate change. In this review, we examine this ongoing loss of Arctic sea ice across all seasons. Our analysis is based on satellite retrievals, atmospheric reanalysis, climate-model simulations and a literature review. We find that relative to the 1981–2010 reference period, recent anomalies in spring and winter sea ice coverage have been more significant than any observed drop in summer sea ice extent (SIE) throughout the satellite period. For example, the SIE in May and November 2016 was almost four standard deviations below the reference SIE in these months. Decadal ice loss during winter months has accelerated from −2.4 %/decade from 1979 to 1999 to −3.4%/decade from 2000 onwards. We also examine regional ice loss and find that for any given region, the seasonal ice loss is larger the closer that region is to the seasonal outer edge of the ice cover. Finally, across all months, we identify a robust linear relationship between pan-Arctic SIE and total anthropogenic CO2 emissions. The annual cycle of Arctic sea ice loss per ton of CO2 emissions ranges from slightly above 1 m2 throughout winter to more than 3 m2 throughout summer. Based on a linear extrapolation of these trends, we find the Arctic Ocean will become sea-ice free throughout August and September for an additional 800 ± 300 Gt of CO2 emissions, while it becomes ice free from July to October for an additional 1400 ± 300 Gt of CO2 emissions.

6. Conclusions

Through novel analysis and a review of recent studies, we have examined the ongoing ice loss of Arctic sea ice across all seasons. We have established the following key results:

• 1.  
  With respect to the 1981–2010 reference period, relative ice loss has been more significant during autumn, winter and spring the last two years than during summer (figure 1).
• 2.  
  The ice cover has not only retreated in its areal extent, it has also become much younger (figure 4) and thinner (figure 5) in recent years. In April 2018, only about 2% of the winter sea-ice cover consisted of sea ice older than 5 years, compared to almost 30% of the April sea-ice cover in 1984.
• 3.  
  The thinning of the ice cover and the overall warming of the Arctic have increased the likelihood of rapid ice-loss events during summer in recent years (figure 6). On the other hand, the larger expanses of open water have similarly increased the likelihood of rapid ice-growth events during autumn.
• 4.  
  The increasing relative loss of winter sea ice is in part related to the fact that more and more regions of the Arctic Ocean completely lose their sea-ice cover during summer (figure 2). This limits the potential for a further acceleration of summer sea ice loss, and causes accelerating sea ice loss during winter.
• 5.  
  Accelerated sea ice loss during all months of the year is additionally driven by a lengthening of the melt season. As assessed for the Arctic as a whole through April 2018, melt onset is occurring 3 days earlier per decade, and freeze-up is happening 7 days later per decade (figure 3). Over the 40 year long satellite record, this amounts to a 12 day earlier melt onset and a 28 day later freeze-up.
• 6.  
  The recent winter sea ice loss is driven by increased inflow of warm air from the south and an overall warming of the Arctic, which both have substantially reduced the number of freezing degree days in recent years (figures 8 and 9).
• 7.  
  The primary cause of the ongoing changes in all months are anthropogenic CO₂ emissions, with a clear linear relationship between sea ice loss and cumulative anthropogenic CO₂emissions in all months (figure 7). The sensitivity ranges from an ice loss per ton of anthropogenic CO₂ emissions of slightly above 1 m² during winter, to more than 3 m² throughout summer.

 

This last finding possibly has the largest policy implications of all our results: based on the study of Notz and Stroeve (2016), it allows us to estimate the future seasonality of the Arctic Ocean directly from the observational record (figure 10). Extrapolating the linear relationships into the future, we find that the Arctic Ocean completely loses its ice cover throughout August and September for an additional roughly 800 ± 300 Gt of anthropogenic CO₂ emissions. For an additional 1400 ± 300 Gt of anthropogenic CO₂ emissions, we estimate the Arctic to become sea-ice free from July throughout October (see Notz and Stroeve 2018 for details on these estimates, in particular regarding the uncertainty arising from internal variability).Given today's emission rate of about 40 Gt CO₂ per year, the time window is closing very rapidly to preserve Arctic sea-ice cover all year round.

 

 

 

[csnavywx]

It's an extrapolation, but it more or less matches up with the middle estimate of the board members (2030s).

[bdgwx]

So by their estimate ice-free conditions will happen sometime between 2030 and 2045. That's not really out of line with other estimates. With each new study it's looking more and more likely that it'll take a miracle to make it to 2050. The IPCC is probably going to have to quicken the pace on their estimates for the AR6 report due out in 2020 or 2021.

[csnavywx]

Especially if this recent winter warmth becomes a more frequent thing -- which is hard to tell at this point. The collapse in freezing degree days over the past 3 winters has been remarkable and has only been offset by remarkably good ice retention weather in summer. However, we're only about 2C away from winter temps causing melt season collapses almost regardless of summer weather (this year's collapse in the Beaufort sector despite otherwise cooler and cloudier-than-normal weather is a good illustration of that).