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Human activity is driving retreat of Arctic sea ice

What the science says...

Select a level... Basic Intermediate

Thick arctic sea ice is undergoing a rapid retreat.

Climate Myth...

Arctic icemelt is a natural cycle

"In 2007, the Northern Hemisphere reached a record low in ice coverage and the Northwest Passage was opened. At that point, we were told melting was occurring faster than expected. What you were not told was that the data that triggered this record is only available back to the late 1970s. We know the Northwest Passage had been open before." (Matt Rogers)

At a glance

The Northwest Passage is the sea route around the waters off northern Canada and Alaska. Its discovery and eventual navigation involves a fascinating tale of endeavour, adventure and tragedy, too, for some expeditions ended in disaster.

Of the many mishaps, by far the worst was that which befell Sir John Franklin and the 128-strong crews of his two ships: they were last heard of in 1845. It took many expeditions and almost ten years before their fate was finally pieced together. One thing became clear by then: the Northwest Passage does not take prisoners. Yet at the same time, those searches for Franklin and his crew generated lots of new chart cover of the waters between the islands making up the Canadian Archipelago.

Complete navigation of the Northwest Passage was finally accomplished by Norwegian explorer Roald Amundsen between 1903 and 1906. Amundsen's boat was relatively small at 47 tons and 70 feet long but usefully it had a very shallow draft. That meant it was able to pass through areas where a bigger boat would have fouled the bottom, thus offering a wider choice of courses to take. Amundsen's route was criticised in some circles because of that factor - what was the point of making the crossing if bigger freight ships could not? But Amundsen was motivated not by money but by science.

With his experienced crew of six, they spent two winters off the eastern side of King William Island, about halfway through the archipelago, collecting data on Earth's magnetic pole and local meteorology, traded with the Inuit and developed hunting and fishing skills. Leaving there in August 1905, they reached Nome, Alaska twelve months later. The ice had pinned them in for a third winter. There was not to be a single-season crossing for another 38 years, when Sergeant Henry Larsen of the Royal Canadian Mounted Police managed it in a schooner.

So yes, while the Northwest Passage was successfully navigated before 2007, the current state of the sea ice means that the picture is now quite different. Part of the reason for that is down to the age of much of the Arctic sea ice today. Sea ice that has yet to experience a summer melting season is known as first-year ice. It's relatively thin, fragile and more vulnerable to melting compared to the ice that has withstood one or more melting-seasons, known as multiyear ice. Multiyear ice can even give a good ice-breaker a run for its money. But now there's a lot less of it.

During many recent summers the Northwest Passage has become open: freight ships and even cruise liners have steamed through. That doesn't mean it's risk-free of course - there are still icebergs to watch out for. Nevertheless, it's getting to the point where there are various concerns being voiced about the number of ships passing through the area, on both ecological and political grounds. For the Northwest Passage, global warming really is a mixed blessing.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

Arctic sea ice has aptly been termed a "canary in the global warming coal mine". In other words, it is regarded as a sensitive indicator of manmade climate change. Because of that importance, climate science deniers will often attempt to fob off the decline of Arctic sea ice as a natural phenomenon.

Satellite measurements of Arctic sea ice extent (fig.1) reveal a rapid decline over the past 45 years, particularly at the end of each year's annual melt season. The downward trend and the increasing difference between seasons are both in keeping with predictions of the effects of global warming.

Monthly sea ice extent anomalies.

Fig. 1: Monthly sea ice extent anomalies (solid lines) and linear trend lines (dashed lines) for March (black) and September (red) from 1979 to 2021. The anomalies are relative to the 1981–2010 average for each month. Image: American Meteorological Society State of the Climate 2021 (index here).

As the Arctic warms, the volume of ice in the region gradually declines. In particular, the thicker multiyear ice that used to be present in abundance has declined significantly (fig 2). Instead, today's ice-pack is dominated by first-year ice that is far more prone to seasonal melt. Combined with natural factors such as storms, this vulnerability can sometimes produce huge melt years such as 2012's record-buster.

 Age of the ice pack.

Fig. 2: The age of the ice pack—which has been observed since the 1980s is used as a proxy for ice thickness. In mid-March 1985 (left), the winter maximum ice pack was dominated by ice at least 4 years old (white). In 2021 (right), only a small strip of very old ice remained tucked up against the islands of the Canadian Arctic. More than half of the winter ice pack was less than a year old (dark blue). NOAA image, based on data from the National Snow and Ice Data Center. Original can be found here.

So, how can one expect climate science deniers to claim all of this melting is simply natural? A popular misinformation-technique is to state that we are just seeing the effects of multidecadal natural cycles causing deep swings in Arctic sea ice coverage and volume. Direct observational support for such 'cycles' is of course impossible. Convenient, eh? Since 1979, we have relied upon direct observations of sea ice extent with contemporary instruments aboard satellites. That's not a long time in the grand scheme of things. What about before then?

In fact, thanks to ocean sediment cores and other physical clues left behind by past climate regimes, we do have pretty good insight into past Arctic sea ice extent. Combining various sources of information about past climate behaviour, we can figure out why changes in ice coverage have occurred in past times.

Natural climate variations have indeed caused significant changes in past Arctic ice extent. Of course they have. But it's important to remember that such changes in no way constitute airtight arguments against modern ice-loss being contributed to by anthropogenic global warming. Events of the pre-industrial past obviously had other causes. Today's losses of sea ice can in contrast be partly attributed to our disruption of the Carbon Cycle through fossil fuel-burning. Indeed, comparisons between past and present Arctic climate reveal different reasons for past and modern sea ice changes (Overpeck et al. 1997). Meanwhile, analysis of several hundred markers of past Arctic sea ice extent tells us that recent losses appear to have no parallel in records going back many thousands of years (Polyak et al. 2010).

Evidence from the past two hundred years shows how natural and anthropogenic influences on Arctic sea ice can be distinguished. Data demonstrate that the Arctic underwent an unusually cool period in the early 19th century. That was followed by recovery to milder conditions extending all the way into the 20th century. After the middle of that century, we see the accelerated warming of recent decades. This pattern is in good agreement with other observations of global warming such as increasing air and ocean temperatures.

It is worth saying again: both observations and model simulations indicate that the nature of the Arctic warming in the last two decades is distinct from the early twentieth-century mild period. Recent, additional reductions in Arctic sea ice are mostly caused by a new, anthropogenic mechanism (Johannessen et al. 2004) and are thus unique in Earth's history.

Last updated on 25 February 2024 by John Mason. View Archives

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Further viewing

The following animation shows how the oldest thickest sea ice has been progressively flushed from the Arctic Ocean over the last two decades. The colours are an indication of the age of the sea ice. Lighter colours are older sea ice - white is 10 years old.


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Comments 26 to 50 out of 58:

  1. Eric @25, Actually I agree with you re #24. With that said, we have had two winters, back-to-back as it happens with incredibly low bouts of the AO, but two data points are obviously not enough to establish whether or not this marks the beginning of a long-term trend. I'm curious to see whether this is evidence of a transition to a new state or simple internal climate variability. Time will tell. The mechanisms and physics behind Arctic amplification in this case, are very well established.
  2. Re # 23, Am I missing something? A negative Arctic Oscillation allows cold Arctic air to slide south, while warmer southern air moves north. Wouldn't this effectively slow recovery of the ice during winter?
  3. True @27, Essentially, in broad terms, yes. Arctic sea ice extent in December 2010 and January 2011 have been running at or near record lows. Hudson Bay only froze over completely over a month later than average. There is still no sea ice along the Labrador coast.
  4. #27 Trueofvoice, yes, recovery is slower due to the negative AO (and negative NAO) bringing lots of very warm air into NE Canada. It's possible we could see the negative AO regime bringing us less ice in general. #26 Albatross, I agree that it is too short a time period to tell if negative AO is a trend or just a random excursion. The paradox paper in the other thread called it red noise causing episodic behavior.
  5. Muoncounter, in the Science is Settled thread you said "What is becoming apparent is that prior predictions of these 'larger changes' were conservative. That suggests the natural cycles aren't so natural any more." I agree that the local warming feedback you referred to there is probably underestimated. What you did not consider in that thread is that the (likely natural) cycle of positive AO in the first half of the 90's also contributed to ice loss. What we will need to look at next is whether the ice loss from AGW and local feedback overwhelms the recovery we should see from negative AO and La Nina. Amd as I said in my previous post we still don't know the effect of AGW and ice loss on the AO.
  6. #30:"we still don't know the effect of AGW and ice loss on the AO." Eric, It might be useful to determine whether ice loss can be modeled by a combination of AGW and AO. If that is correct, there ought to be a long term trend with residuals. See the graphs here, here and here for ideas about the trend; quadratic looks reasonable. The oscillation's timing should be tested against any periodicity in these residuals. If the magnitude of the residuals is small, it would indicate that the oscillation is relatively weak as a driver of ice loss.
  7. From here. "the ice cap extents over the last 60 years the north pole all but completly melts EVERY YEAR." Sorry, Briago, but that's just not true; the Arctic polar ice does not all but completely melt each year. The NSIDC has excellent data; see their October 2010 press release for a recent summary. One of the great things about SkS is the information here is based on research and data. In short, facts. Most of the posters also strive to substantiate their claims with evidence. If you are serious about the subject of climate change (and you should be), please put your opinions on hold for a while, look around and learn.
  8. An interesting historical record of life and Arctic Sea Ice.

    [DB] Hot-linked URL.

  9. Camburn, You need to stop posting gibberish about things you do not know. This Wikipedia article documents that the entire Northwest passage was ice filled until 10 years ago. Your assertion that it has been passable by non-icebreaking vessels for decades is simply untrue. Capt. Larsens voyage has been replicated in recent years, in only a few weeks to make the passage, it is no longer remarkable for a light icebreaker to transit the NW passage. It is remarkable that someone who posts so little data is so fast to question scientists who actually measure the Arctic ice. How can you question that work when you have no idea how they measured it?
  10. michael: Capt Larson made the voyage in 1944 through the northern route. Even last year his route was not passable. Live with it, it is history. IF you lived near the Arctic, you may know that the Canadian Coast Guard replenishes supplies on an annual basis to the northern stettlements. It has been doing this for decades. Just the way it is. During WW2, the Northest Passage was also sailed by German Warships......remember? If you don't you can look it up. Some simple history items are well known. How can I question cyrosphere? Quit easily. It is a graph posted with no supporting data prior to 1979. Sorry that my 3.5 prediction with the support of the Shindell/Schmidt paper, russtles your feathers it seems.

    [DB] Assertions without links to sources will be disregarded.  IIRC, the Komet took the NE passage, not the fabled NW passage (so even that does not help you).

    BTW, Climate4you is a blind guide: it will lead you astray.

    "How can I question cyrosphere?  Quit easily.  It is a graph posted with no supporting data prior to 1979."

    Study this link for a history of Arctic Sea Ice, how to find the data on it...and how to properly analyze it.

    Or you can email your questions to the good people at the Arctic Climate Research at the University of Illinois here:

  11. Fortuitously, Peter Sinclair has just posted this item on why the melt is so fast. Yet another reminder that air temperature and SST cannot give us the whole story.
  12. In 2007, a lightweight catamaran made the 3,200-mile Northwest Passage voyage entirely by sail. Peter Semotiuk, who runs a single-band sailor's radio network at a port in the middle of the passage, completed the voyage in 1988 and said: "This summer [2007] the passage was largely wide open. It's a very different picture to say 20 years ago, when I travelled the length of the passage." Corporal Henry Larsen's St. Roch was made from extra thick timbers of Douglas Fir, sheeted in Australian gumwood and powered by a diesel engine. University of Calgary: The Larsen Expeditions BBC: Plain sailing on the Northwest Passage
  13. The catamaran passage wasn't a freak event either. 30 recreational boats have completed the voyage in the past decade. The ease of passage through the Northwest Passage is a matter of significant political importance for Canada, the US & Russia. Parliament of Canada: The Northwest Passage and Climate Change
  14. #35, also worth reading Polyak et al and associated data links within to get a context of Arctic ice variability over the past century and also Holocene. You're embarrassing yourself by suggesting that there has been anything other than a sharp decline in Arctic ice since about the 1970s. The last time extents were as low is reasonably well-constrained by dating of wood on old shorelines and of wood trapped in ice shelves - several thousand years ago. [caused by higher Arctic insolation in the early-mid-Holocene]. As Michael Sweet and Bibliovernis have shown, there is no evidence that ice levels in the 1940s were anywhere near today's levels. Anecdotes of sailors commenting on the lack of ice have to be placed in context - a context of a very large amount of ice up there in the early part of the century. Their 'lack of ice' could easily be a great deal of ice by today's standards. A bit like a Scot thinking a day of 20C is hot, which makes sense if you live in Scottish summers, but would make no sense for somebody from Italy!
  15. DB: Note I said the NE passage when talking the Komet. Sorry, but I don't go to climate 4u. skywatcher: Where have I posted that there is not a sharp decline presently in Arctic Ice? I have posted papers that show the variability in Arctic Ice over a long time period. I will state again, for Capt Larson to have made the voyage in 1944 was a feat and a testament to the conditions that year. This also coincides with the period that Greenland had temperatures just slightly lower than present. Here is the route of the St Roch. Note that it went between Banks Island and Victoria Island. Watch the ice this summer and see if this lane is ever passable. Norther Route

    [DB] I looked up your comment:

    "During WW2, the Northest Passage was also sailed by German Warships......remember? If you don't you can look it up. Some simple history items are well known."

    Fortuitous typo?  A thinly veiled attempt at a snarky witticism?  Be it known that your narrative you are pursuing is from the Climate4you/WUWT/CA playbook and that our patience with it...grows thin.

    From time to time you show signs of being an actual skeptic and then you return to form.  So be it.

    Please support assertions with links to peer-reviewed science, construct your comments to comply with the Comments Policy and also ensure that they are on-topic in the future.

  16. This St. Roch nonsense has been done to death many times before, even on SkS. Any way of searching, so that reference can be made to the last thread that went through all this ?

    [DB] Would you care to write up and contribute a guest post on that topic?  :)

  17. With reference to DB's moderator response above, I would be prepared to try to get something written (if only for my own future reference) but I would need to be able to find all previous references to the St Roch on SkS, because I think quite a bit of relevant information is already there - it just needs to be gathered together and researched in more detail. Is there any way of gathering this information ?

    [DB] Short answer: There's no easy way to find a comprehensive listing in all the SkS comments.  A search of various terms will bring up a listing of blog posts containg the terms, but one is still forced to then hunt-and-peck through the sometimes length comment threads.

    If you are interested in doing it, it would be easiest (from a manhours perspective) to start from scratch.

    A good starting point for research:

  18. Here's a new model study, Up and/or down for the next few decades, multiple factors at play. This doesn't quite gel with previous reporting does it?

    [DB] "This doesn't quite gel with previous reporting does it?"

    I doubt that you care to elaborate on your implication here, as I'm pretty sure where you're coming from (and it won't pass the Comments Policy prohibitions).

    Needless to say, that's old news, I'm afraid.  Discussed extensively already at Neven's and RC.  Per Gavin:

    This is not particularly relevant for current behaviour though. More important is how good the aerosol forcing is, or the indirect impacts of black carbon etc. - but we don't know the real answer. - gavin

    Note the bit about "not being relevant for current behavior"...because the ice is currently disappearing in the Arctic 4 times faster than predicted by all models except Maslowski's (which is still tracking for his 2016±3 years).

  19. Schmidt's other comment is also worth repeating. " This is mostly about a quantification of the size of internal variability. By looking at multiple runs with the same forcing and looking at the variability in short trends, you can make a statement about the range. The current trend is at the edge of what the NCAR runs show, and so it is conceivable that what we are seeing has been a weaker forced trend, combined with a (stochastic) increase to the trend because of internal variability. With that assumption, one can look at the other simulations and calculate the likelihood of the stochastic component going the opposite way and slowing down the observed trend. But these likelihoods rely on the NCAR model's estimates of both the forced trend and the internal variability being correct. The former is less likely than the latter"
  20. RyanStarr, setting aside the fact that it IS a new study and thus there hasn't been time to analyze or test its accuracy yet; The study author also said that it should not be taken to mean that the Arctic ice is not retreating. Rather, when they incorporated what they believe to be the possible range of mechanical impacts on sea ice loss (a new form of analysis which they had to assign large uncertainty bands to) they found that the trend over the next 10 years could be either up or down... but that the trend over the next 20 or more years was sharply downward. The biggest problem I see with their argument that the upcoming ten years could see a significant upward trend is that there hasn't been a single previous upward trend of that duration in the satellite record. If you cherry pick very carefully you can find a couple of five year periods where the trend was slightly positive, but nothing close to statistical significance let alone a ten year duration. If they were right about mechanical effects producing a roughly 50% chance of significant 10 year upward trends then we should have seen one by now, or at least something close. Time will tell. However, it doesn't change the fact that we are currently at a record low ice volume, a record low ice area, and a near record low ice extent. The only reason the extent isn't a record low is that the average concentration of the ice pack is. Currently, only ~57% of the ice extent is actually covered in ice (e.g. ice area is 57% of ice extent). Basically, this means that the ice is more spread out than at any previous time in the satellite record. 2007 set the record low extent because winds pushed the ice into a small highly concentrated mass. 2011 currently has an only slightly higher extent despite the ice being the most spread out it has ever been. This is consistent with an example I've been using for a few years; Consider a 10' x 10' x 10' cube: Volume = 1000 cu ft, Area = 100 sq ft, Extent = 100 sq ft Now break it into 1000 1' x 1' x 1' cubes scattered in a 15% concentration: Volume = 1000 cu ft, Area = 1000 sq ft, Extent = 6667 sq ft The same volume of ice, but broken up and spread out it has 10 times the area and 66.67 times the extent. To get extent back down to 100 sq ft, 985 of the 1' x 1' x 1' cubes (98.5%) would have to melt. Obviously that is the extreme case and that kind of perfect breakup and spreading doesn't occur naturally, but it illustrates how it is possible for extent to remain largely unchanged as the ice breaks up and melts away. According to PIOMAS ice volume has set a new record low for the day, each and every day, from 12/20/2009 through 07/31/2011 (the last date data is available for currently). That's 589 consecutive days of new record lows. If the rate of volume decline seen over that time period continued then volume would hit zero in three years. As DB notes, Maslowski's volume projection is the only 'model' which has matched the rate of ice loss over the past five years or so. If that doesn't change in the next few years we'll be seeing only tiny remnants of ice in summers within this decade.
  21. @DB, not sure what you mean, the general message from the AGW supporting side of the argument has been that ice loss is accelerating and will continue to as CO2 levels rise. This study suggests otherwise, that a high degree of natural variability exists in the decadal time frame. They say 50-60 years is required to pass before warming effects become apparent. It would also suggest that any current trend is also natural, unless you want to entertain the notion of 'spurts' of AGW ice loss. This very much contradicts the view popularly expressed on this site, this thread actually. The news isn't so old, it's still August, and hasn't been discussed _here_ at all.

    [DB] For the many reasons stated earlier, the study is essentially a thought experiment not supported by actual observations and metrics.  You were pointed out why it's not applicable to what we observe and measure by myself in my earlier response to you and by CBD in his repy to you above.

    "The news isn't so old, it's still August,"

    Compared to the rate of demise of the Arctic Sea Ice, as ably denoted by muoncounter below, the study is indeed old news.  Obsolete, even.

    "and hasn't been discussed _here_ at all."

    Just because we allow occasional reinvention of the wheel does not also mean we will suffer through continual reinvention of the flat tire.

  22. @CBD, thanks or reply, I think we have to keep in mind how short the current record is, and of course there is a first for everything. With short records we can expect to see lots of 'firsts'!
  23. RyanStarr, most of what you claim this study says or suggests... it does not. Perhaps you should read it before commenting further on 'what it means'.
  24. Ryan#46: "any current trend is also natural," Prove it. Historic records, consistent with modern measurements, say different. Looks like the 'natural cycle' is flat and the recent melt is anything but natural.
  25. CBD: "... it does not." An understatement. Kay et al 2011 say just the opposite of Ryan's claim: On all timescales examined (2–50+ years), the most extreme negative observed late 20th century trends cannot be explained by modeled natural variability alone. ... In a warming world, CCSM4 shows that multi-decadal negative trends increase in frequency and magnitude, and that trend variability on 2–10 year timescales increases. --emphasis added

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