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The unnoticed melt

Filed under: — group @ 9 September 2011

Guest commentary from Dirk Notz, MPI Hamburg

“Well, it’s not really good timing to write about global warming when the summer feels cold and rainy”, a journalist told me last week. Hence, at least here in Germany, there hasn’t been much reporting about the recent evolution of Arctic sea ice – despite the fact that Arctic sea ice extent in July, for example, was the lowest ever recorded for that month throughout the entire satellite record. Sea-ice extent in August was also extremely low, second only to August 2007 (Fig. 1). Whether or not we’re in for a new September record, the next weeks will show.

Figure 1: Evolution of Arctic sea-ice extent in July and August from 1979 until 2011. (NSIDC)

A rainy summer might be one reason for an apparent lack of public attention with respect to the ongoing sea-ice loss. Another reason, however, is possibly the fact that we scientists have failed to make sufficiently clear that a major loss of sea ice during the early summer months is climatologically more important than a record minimum in September. This importance of sea-ice evolution during the early summer months is directly related to the role of sea ice as an efficient cooling machine: Because of its high albedo (reflectivity), sea ice reflects most of the incoming sunlight and helps to keep the Arctic cold throughout summer. The relative importance of this cooling is largest when days are long and the input of solar radiation is at its maximum, which happens at the beginning of summer. If, like this year, sea-ice extent becomes very low already at that time, solar radiation is efficiently absorbed throughout all summer by the unusually large areas of open water within the Arctic Ocean. Hence, rather than being reflected by the sea ice that used to cover these areas, the solar radiation warms the ocean there and thus provides a heat source that can efficiently melt the remaining sea ice from below. In turn, additional areas of open water are formed that lead to even more absorption of solar radiation. This feedback loop, which is often referred to as the ice-albedo feedback, also delays the formation of new sea ice in autumn because of the accompanying surplus in oceanic heat storage.

Measurements from ice buoys show that indeed melting at the bottom of the sea ice has increased significantly in recent years. While field experiments that were carried out in the 20th century showed unambiguously that surface melting used to be the dominant mechanism for the thinning of Arctic sea ice, now in larger and larger areas melting at the underside of the ice is almost equally important. Such melting from below is particularly efficient since the temperature at the ice-ocean interface is fixed by the phase equilibrium that must be maintained there. Hence, any heat provided by the ocean to this interface will lead to thinning of the ice in summer and to slower ice growth in winter. At the surface, the ice temperature is not fixed as long as the ice isn’t melting, and heat input from the atmosphere can in part be compensated for by a change in surface temperature and an accompanying change in outgoing long-wave radiation at the ice surface.

In addition to these climatological reasons, there is another reason for why a public focus on just the September sea-ice extent is possibly misleading: Such focus might give the impression that sea-ice extent is stable in other seasons but summer. That this is not the case becomes obvious from the graphical distribution of extreme sea-ice extent for each individual month that is shown in Figure 2. The figure shows in red the years with the five lowest values of sea-ice extent for a certain month and in blue the years with the five highest values. A retreat of sea ice throughout the entire year is obvious. In fact, the sea-ice extent for every month since June 2010 has been among the five lowest values ever recorded by satellites.

Figure 2: Distribution of record minima and record maxima of Arctic sea-ice extent (NSIDC). The years with the five lowest values of sea ice extent for a certain month are marked in red, those with the five highest values of sea-ice extent are marked in blue. The darkness of the color indicates the ranking: the darkest red marks the lowest value, the darkest blue the highest.

Such widespread loss of Arctic sea ice has sometimes given rise to the concern that the total loss of Arctic sea ice at least during summer time can no longer be avoided. In this context, usually the ice-albedo feedback is mentioned, since it provides a mechanism that can in principle lead to a so-called “tipping point” beyond which the loss of the remaining sea ice becomes unstoppable. However, recent research shows that this scenario is too pessimistic. For example, in a paper published in Geophysical Research Letters in January 2011, Tietsche et al. [1] used climate model simulations to examine the evolution of Arctic sea ice after an extreme loss event. In their model simulations, they artificially removed all Arctic sea ice at the beginning of June for selected years and examined if the ice would recover from such extreme event.

Their main result is shown in Fig. 3: It took only about two years after each complete sea-ice removal until the ice had recovered to roughly the extent it had before the removal. Hence, sea ice extent is primarily defined by the prevailing climate conditions; the ice-albedo feedback mechanism is, in isolation, too weak to stabilize a very low sea-ice cover. In examining the mechanisms behind this finding, Tietsche et al. found that unusually large amounts of heat indeed accumulate in the ocean during the ice-free summer. However, this heat is efficiently released to the cold atmosphere already during the following autumn and winter. Once that heat release has cooled the ocean to its freezing temperature, sea ice forms again. Because this ice is initially very thin, the efficient release of heat from the ocean continues for some time, causing a rapid growth of the new sea ice. Much of this ice then survives the following summer, and sea-ice conditions can quickly return to those before the artificial perturbation.

Figure 3: Evolution of September sea-ice extent in coupled climate model simulations. The blue curve shows the evolution of the unperturbed sea-ice extent for the A1B scenario, with the gray shading showing the ensemble spread of three model runs. For the red curves, sea ice was artificially removed at the beginning of June in 1980, 2000, 2020, 2040 and 2060 within the climate model simulations. For all these perturbations, sea-ice extent recovered rapidly to the unperturbed extent. A similar result was found for sea-ice volume.

The finding that the long-term evolution of Arctic sea ice is primarily governed by the prevailing climate conditions implies that the loss of Arctic sea ice can still be slowed down and eventually stopped if an efficient reduction of CO2 emissions were to become reality soon. Last week, however, it became obvious once more how unlikely such scenario is: On 30th August, Exxon announced a deal with Rosneft, the Russian state oil company. As part of this deal, Exxon will invest more than US$2 billion to support Rosneft in the exploitation of oil reserves in the Kara Sea, which is part of the Arctic Ocean north of Siberia. One requirement for the success of this deal: a further retreat of Arctic sea ice. Given that climate model simulations indeed all project such further retreat of Arctic sea ice, it seems that at least to some degree, managers of big oil companies have started to make business decisions based on climate-model simulations. That may be good news. Or not.

This article is in part based on a German article that was published at Klimalounge.


  1. S. Tietsche, D. Notz, J.H. Jungclaus, and J. Marotzke, "Recovery mechanisms of Arctic summer sea ice", Geophysical Research Letters, vol. 38, pp. n/a-n/a, 2011.

172 Responses to “The unnoticed melt”

  1. 51
    prokaryotes says:

    @ JBar,
    they found alligator sceletons near the north pole.

    Fossil animals found in Arctic Canada (Nunavut Territory) provide a snapshot of fish evolving into land animals, scientists say. The 383 million-year-old specimens are described as crocodile-like animals with fins instead of limbs that probably lived in shallow water.


    The creature shares some characteristics with a fish; it has fins with webbing, and scales on its back. But it also has many features in common with land animals. It has a flat crocodile-like head with eyes positioned on top and the beginnings of a neck – something not seen in fish.

    “When we look inside the fin, we see a shoulder, we see an elbow, and we see an early version of a wrist, which is very similar to that of all animals that also walk on land,” said Professor Shubin. The scientists think the creature lived in the shallows “Essentially we have an animal that is built to support itself on the ground.”

    The scientists believe the position of the creature’s eyes suggest it probably lived in shallow water. “We are capturing a very significant transition at a key moment of time. What is significant about the animal is that it is a fossil that blurs the distinction between two forms of life – between an animal that lives in water and an animal that lives on land.”

    And here is a more recent discussion, related:

    Patrick, much as we might gasp at the implications, a seasonally sea-ice free Arctic Ocean is NOT a stable climate regime. Numerical Modeling and Paleoclimate Studies indicate that there are two stable regimes for the Arctic Ocean in a warming Climate: perpetually ice-covered, and perpetually ice-free.

    These modelling result were published by Eisenman and Wettlaufer (2008) “Nonlinear threshold behavior during the loss of Arctic sea ice”. The paper (and it’s SI Appendix), is freely available from the Journal Proceedings of the National Academy of Sciences.

    Figure 3 Bifurcation diagram for the full nonlinear model

    The description of “Fig. 3” says in part:
    “Under a moderate warming (ΔF0 = 15 Wm−2), modeled sea-ice thickness varies seasonally between 0.9 and 2.2 m. Further warming (ΔF0 = 20 Wm−2) causes the September ice cover to disappear, and the system undergoes a smooth transition to seasonally ice-free conditions. When the model is further warmed (ΔF0 = 23 Wm−2), a saddle-node bifurcation occurs, and the wintertime sea ice cover abruptly disappears in an irreversible process.”

    Above, “ΔF0 = 15 Wm−2” should be read as “Change in Climate Forcings relative to Time Zero” in Units of Watts per square meter. This means that after the first Sea ice free September, Climate forcings need to increase by only 3 watts per square meter until the Arctic Sea Ice disappears permanently, and irreversibly. Methane Clathrates alone have the potential to increase Climate forcing by 5 W/m^2, in addition to our continued release of C02.

    Recent Paleoclimate studies show the Arctic had a perennially sea ice free ocean, an mean annual temperature over 12C, and fossilized Crocodile skeletons found on Baffin Island, the place where many current Commenters speculate will be the last stand for Arctic Sea Ice.

  2. 52
    Phil. says:

    Eric your comment only applies to one polarization that’s why Polaroid sunglasses are so useful!
    Google Brewster angle.

  3. 53
    Kevin O'Neill says:

    prokaryotes #51 – the Canadian Arctic 350 mya, as part of Pangaea, is usually depicted on maps as being relatively close to the equator. So finding fossils in Canada of animals that lived in tropical climates should not be surprising.

  4. 54
    Philippe Chantreau says:

    Prokaryotes, 383 million years ago, what was the latitude of the location where the croc fossiles were found? I would think that landmasses have changed and moved quite a bit since then. What was the whole Earth climate like back then? Any best guess on what kind of CO2 concentrations were present? Context helps.

  5. 55
    Nick Barnes says:


    1. No ice on June 1, 2020
    2. Ice grows again during winter 2020-21
    3. Ice is at 1.7 on June 1, 2021
    4. Ice melts out maybe by July 1, 2021
    5. Ice grows again during winter 2021-22

    Where do you get this? From reading the paper, what they do is remove all the ice on July 1, 2020 (not June). In September 2020 there is no ice. In September 2021 there is about 1.7 Mkm^2 of ice. In September 2022 there is about 4 Mkm^2. I’m reading those numbers from figure 1, which only has numbers for September. Where are you getting your numbers for June 1 2021 and July 1 2021? I see no such numbers in the paper.

  6. 56
    Marcus says:

    Hi Prokaryotes,

    Due to continental drift, a fossile 373 million years old I would not expect to have died even close to the north pole. But there is evidence that the arctic was free of ice most of the time


  7. 57
    Jbar says:

    @Bruce 38
    Agreed, as evidenced by the area north of Scandinavia staying ice-free all winter, but even in 2080 ocean currents should not be warm enough to keep the whole arctic region ice free all winter (although the winter maximum extent should be reduced from today’s 13mm km2 area to perhaps 9-10mm km2).

  8. 58
    Jbar says:

    @Steve 44
    “Well, maybe we can use wind to upgrade the radiator … in winter. What if ice area can be reduced, to decrease the winter insulation and increase heat loss from the Arctic Ocean to the long night? Instead of Figure 3 above (in which sea ice is disappeared in June), what if sea ice can be disappeared (or compressed) in winter — every year? Can we lose enough energy to space to slow the warming of the planet?”

    The way to increase radiant energy loss to space is to increase polar/surface temperature or to reduce the radiant transfer resistance (less GHGs). Unfortunately increasing the temperature increases water vapor (a GHG) which increases the resistance in a non-linear(?) feedback. (Perhaps the increase in water vapor from very low levels with increasing temperature is a big reason why the poles warm faster than warmer latitudes?)

    I don’t know how we could practically or economically increase ocean and air currents (energy transfer) toward the arctic to warm it. It might also measurably increase GHG rate of change (fossil fuels to provide the energy to do it).

    I guess if you remove ice, the ocean surface is not much less than a few degrees below 0C rather than as low as -80C for the ice surface, so removing the ice should very sharply increase radiant losses, but once the ocean reaches 0C, the ice will reform very quickly and want to go down to minus 60-80C again. It is a monumental Sisyphean chore. Again, how could we practically or economically do that? Fleet of ships to push the ice south where it can melt?

    Seems like a possibility worth exploring some more? Anyone?

  9. 59
    Jbar says:

    @prokaryotes 51
    Wow – I MUST look up that paper. Dramatic conclusion. “Actual” (er, modeling) evidence for a bona fide tipping point (for year round arctic sea ice) not much beyond the total loss of summer sea ice! I’ll bet you can be sure that when arctic ice is gone year round it’s curtains for the Greenland ice cap and hello 10-20m sea level rise (Greenland + destabilized West Antarctic)!

    WRT fossil alligators in arctic, wasn’t this around the Paleocene/Eocene Climate Optimum (circa -50MM years) ? Two factors –
    1) much higher atmospheric CO2 than today.
    2) If there was a south polar land mass at that time, it must not have had a circumpolar current to act as an energy transfer barrier from lower latitudes.

    With its isolating circumpolar current (which came about after the disappearance of several land bridges circa -30MMa(?)), the Antarctic land mass is stuck in an icehouse condition, helping to cool the entire planet and requiring dramatically higher CO2 levels to thaw it out. I wonder if the arctic could get warm enough to have alligators again as long as there is a “permanent” southern ice cap?
    However, if there is a model that says so, we must consider the possibility.

  10. 60
    Bruce Tabor says:

    @ prokaryotes
    The Eisenman paper is fascinating. I’m still digesting it.

    I don’t think the ΔF0 in the paper relates to the global average forcing (now about 1.5 W/m^2), but to a local Arctic forcing, which will be greater than the global average.

    Their simulation is only one-dimensional, so in that respect is even more limited than the GCMs. It is a little hard to match with Tietsche’s paper, as by design Eisenman is assuming no “horizontal” heat transfer.

  11. 61
    Jeffrey Davis says:

    There’s a funny typo in the paper:

    The resulting area of the Arctic Ocean is 8.4 · 10^12 m^2 sq miles.

    8,400,000,000,000 square miles!

  12. 62
    prokaryotes says:

    It seems that during different times in earth past, different kinds of crocodiles appeared when climate change triggered evolution. I agree kind of hard to reconstruct the correct spot of the crocodile from 383 m years ago, judging from a single site. But after that, later they found other crocodile fossils too, near the pole. Would be nice if someone can link to earlier crocodile skeleton findings. Not sure but James Lovelock mentioned this too and a much earlier species, i believe.

  13. 63
    Tony O'Brien says:

    Tietsche et al point out that the loss the ice insulation effect works both ways; lets more heat in in summer and more heat out in winter. Also in winter thin ice forms very quickly.

    Recovery is not back to pre industrial, or even to today’s levels. Recovery is to the then normal.

    A very readable paper.

  14. 64
    arch stanton says:

    Prokaryots – This animation shows the protocontinents’ evolution through the assembly and breakup of Pangaea (with the equator being held constant). Use your browser stop button to halt the process at about 383 million years or so and you will see that – what is to become the far North American continent was actually fairly close to the equator at the time:

    hth arch

  15. 65
    prokaryotes says:

    The hypothesis that the crocodile ended up at baffin island through continental drift is weak.

    August 12, 2010

    Giving new meaning to the phrase “older than dirt,” scientists have found evidence of an underground rock reservoir left over from the days when Earth was a ball of magma, a new study says.

    Rocks recently found on Canada’s Baffin Island erupted as lava from a deep rock reservoir that formed 4.5 billion years ago, when the solar system was new, the study says. The reservoir may hold the world’s oldest rock, according to the authors.

    (Related: “Oldest Rocks on Earth Discovered?” [2008].)

    Baffin Island (Inuktitut: ᕿᑭᖅᑖᓗᒃ, Qikiqtaaluk, French: Île de Baffin, Old Norse: Helluland) in the Canadian territory of Nunavut is the largest member of the Canadian Arctic Archipelago. It is the largest island in Canada and the fifth largest island in the world,

    There is also a small island called Alligator island.

  16. 66
    prokaryotes says:

    How Tortoises and Alligators Survived on Ellesmere Island 50 Million Years Ago

    A new study of the High Arctic climate roughly 50 million years ago led by the University of Colorado at Boulder helps to explain how ancient alligators and giant tortoises were able to thrive on Ellesmere Island well above the Arctic Circle, even as they endured six months of darkness each year.

    The new study, which looked at temperatures during the early Eocene period 52 to 53 million years ago, also has implications for the impacts of future climate change as Arctic temperatures continue to rise, said University of Colorado at Boulder Associate Professor Jaelyn Eberle of the department of geological sciences, lead author of the study.
    Biogenic Apatite from Bones and Tooth Enamel

    The bone and tooth enamel of vertebrate fossils contains biogenic apatite — a mineral that is fossilized after the death of living organisms and which can be used as a “flight recorder” to infer paleoclimate conditions. Since all of the fossil materials were from the same stratigraphic layer and locality, the oxygen isotope ratios from the animals are linked to the temperatures of both ingested river water and precipitation at the time, allowing them to better estimate temperatures in the Eocene both annually and seasonally, she said.

    “We use the water that the animals were drinking as a proxy for paleotemperature,” said Eberle. “In mammal fossils, for example, we can analyze the oxygen isotope ratios in a sequence along the length of a large fossil tooth and estimate the warm-month and cold-month averages during the Eocene because teeth grow year round. When it comes to oxygen isotope values in tooth enamel, what we found for these creatures is that you are what you drink,” she said.

    The team looked at teeth from a large, hippo-like mammal known as Coryphodon, as well as bones from bowfin fish and shells and bones from aquatic turtles from the Emydidae family, the largest and most diverse family of contemporary pond turtles. While Coryphodon and bowfins grew throughout the year, the turtles exhibited shell growth only during summer months, much like turtles that live today in non-equatorial areas.

    Eberle said the new study implies Eocene alligators could withstand slightly cooler winters than their present-day counterparts, although data from captive alligators show they are heartier than other members of the crocodilian family and can survive short intervals of subfreezing temperatures by submerging themselves in the water.

    In contrast, the existence of large land tortoises in the Eocene High Arctic is still somewhat puzzling, said Eberle, since today’s large tortoises inhabit places like the Galapagos Islands where the cold-month average temperature is about 50 degrees F (10 degrees C.)

  17. 67
    prokaryotes says:

    Dramatic interannual changes of perennial Arctic sea ice linked
    to abnormal summer storm activity

    James A. Screen,1 Ian Simmonds,1 and Kevin Keay1
    Received 24 February 2011; revised 4 April 2011; accepted 4 May 2011; published 4 August 2011.
    [1] The perennial (September) Arctic sea ice cover exhibits large interannual variability, with changes of over a million square kilometers from one year to the next. Here we explore the role of changes in Arctic cyclone activity, and related factors, in driving these pronounced year‐to‐year changes in perennial sea ice cover. Strong relationships are revealed between the September sea ice changes and the number of cyclones in the preceding late spring and early summer. In particular, fewer cyclones over the central Arctic Ocean during the months of May, June, and July appear to favor a low sea ice area at the end of the melt season. Years with large losses of sea ice are characterized by abnormal cyclone distributions and tracks: they lack the normal maximum in cyclone activity over the central Arctic Ocean, and cyclones that track from Eurasia into the central Arctic are largely absent. Fewer storms are associated with above‐average mean sea level pressure, strengthened anticyclonic winds, an intensification of the transpolar drift stream, and reduced cloud cover, all of which favor ice melt. It is also shown that a strengthening of the central Arctic cyclone maximum helps preserve the ice cover, although the association is weaker than that between low cyclone activity and reduced sea ice. The results suggest that changes in cyclone occurrence during late spring and early summer have preconditioning effects on the sea ice cover and exert a strong influence on the amount of sea ice that survives the melt season.

    Impacts of a recent storm surge on an Arctic delta ecosystem examined in the context of the last millennium

    Climate change projections and stratosphere–troposphere interaction

  18. 68
    arch stanton says:

    Prokaryotes claims that evidence is weak that alligators lived in what was to become far North America when it was much closer to the equator 385 MILLION years ago. To back up this claim a study is cited concerning 4.5 BILLION years ago that makes no claim as to the latitude of the geology in question at either the time in question or 4.5 billion years ago.

    Prokaryotes then attempts to move the goal posts by citing a publication that misleadingly uses the term “alligator” in it’s headlines when the term “alligator” is never used in the paper itself. The paper does use the term “emydid turtle” however which are known to be found well out of equatorial regions and unlike the alligator, can currently be found in much of North America (perhaps not Elsmere island) and to HIBERNATE.

    One of the authors of the paper extrapolates about how Eocene alligators may have withstood colder temperatures that today’s alligators but NOWHERE in the article OR the paper does it mention that Eocene alligators were found on Elsemer island.

    The topic at hand (Prokaryotes brought it up) was Paleozoic (Devonian) alligators.

    Even a eukaryote can see that the goal posts have been moved out of the stadium. (Today is one of *those* Sundays after all).

  19. 69
    prokaryotes says:

    The point is that there are many crocodile links.

    And that there is “evidence” – from the paper the first sentence…

    “As a deep time analog for today’s rapidly warming Arctic region, early Eocene (52–53 Ma) rock on EllesmereIsland in Canada’s High Arctic (∼ 79°N.) preserves evidence of lush swamp forests inhabited by turtles,alligators, primates, tapirs, and hippo-like Coryphodon.”

    The old rocks from the baffin area suggest, that there have been volcanoes islands from magma, which has been dated 4-5 b years old. This geographic setup is in agreement with the species at hand, low lying swamp like habitats.

    The repeated evidence through earth history of the crocodilian genus at the earth poles suggest that they not only came through continenatal drifts or through land migration. They probably migrated once and then re-inhabited the area when conditions changed.

    When crocodiles roamed the Arctic
    Four years later, Alfred Wegener put forward his theory of continental drift which, it was later realised, could explain the balmy climate: Antarctica had been warmer because it was once much closer to the equator. Even today, some schoolchildren are taught that continental drift accounts for all the evidence for a warmer Antarctica.

    However, the fossil trees Shackleton’s team discovered grew around 250 million years ago, when Antarctica was barely closer to the equator than it is today. What’s more, the continent reached its current position roughly 100 million years ago, and an ever-growing list of fossil finds date from 100 to 40 million years ago. During this time, when dinosaurs roamed the almost subtropical forests of an ice-free Antarctic, conditions on the other side of the planet were even more remarkable: the Arctic Ocean was a gigantic freshwater lake infested with crocodile-like reptiles.

    One of the earliest signs that the poles were ice-free and warm 100 million years ago was the discovery at the turn of the 20th century of fossil breadfruit trees from the Cretaceous in Greenland; today such trees are at home in places like Hawaii. Since then, even more extraordinary finds have been made.

    The most evocative image of a warm Arctic has emerged from the work of John Tarduno of the University of Rochester, New York. For more than a decade, Tarduno has been hunting for fossils on Axel Heiberg Island in the Canadian Arctic, just west of Greenland. The island was already well within the Arctic Circle 90 million years ago.

    His team has found bones and even partial skeletons of a crocodile-like creature called a champsosaur from this period. The champsosaur was a fish-eating reptile up to 2.4 metres long that probably looked much like the gharials of India. Because these reptiles would have relied on their environment to stay warm, conditions in the far north must have been far hotter than today. “These fossils speak volumes,” says palaeoclimatologist Paul Wilson of the University of Southampton in the UK.

    Last year, Tarduno’s team reported that most champsosaur remains are of juveniles, meaning the animals not only lived but bred in the Arctic. As hatchlings and juveniles could not have survived if winter temperatures came anywhere close to freezing, this means it was not only warm, but warm all year round.

    Modern crocodiles are found no further north than the lower Yangtze and North Carolina. If the champsosaurs’ temperature requirements were similar, the Axel Heiberg locality must have had mean annual temperatures of at least 14 °C, and the average temperature during the coldest month could not have fallen below 5.5 °C. The region would not even have had ice in winter.

    The champsosaur was not the only warmth-loving reptile to live inside the Arctic Circle. Tarduno’s team has found an abundance of fossils of four kinds of turtles at Axel Heiberg Island, again pointing to a mean annual temperature of at least 14 °C.

    Most recently, the team has found fossils of a family of turtles called Macrobaenidae on Axel Heiberg Island (the details have yet to be published). These turtles originally lived in Asia, but from the late Cretaceous onwards appeared in North America too. Because turtles are very sensitive to climate, the researchers think they could have survived the migration only if they moved along a route in the far north that was warm all year round. More significantly, these turtles – like the champsosaurs – were freshwater creatures. “They would have required a non-marine connection,” says team member Donald Brinkman of the Royal Tyrrell Museum in Drumheller, Alberta, Canada. “If the Arctic was a big freshwater lake, that would have made it possible.”
    Biggest lake

    Fresh water in the Arctic Ocean? As far-fetched as it seems, there is now strong evidence that as recently as 50 million years ago, at the start of the middle Eocene, at least the surface of the Arctic Ocean was fresh. This picture has emerged only recently because it is extremely hard to access the records of the ocean’s history, says Kathryn Moran of the University of Rhode Island in Kingston, a member of a 2004 expedition to drill sediment cores from the Arctic seabed.

    Drill ships have to stay exactly above their chosen site to prevent the drill from snapping, yet in the Arctic drifting chunks of sea ice up to several kilometres wide make normal drilling operations impossible. “They can easily knock a ship off location,” says Moran. “So what we had to do was break that ice.” The task fell to two icebreakers. “The ships are really big and powerful, and they basically had to learn how to dance together,” says Moran.

    Dance they did, and in 2004 the team collected a core of sediment that had been deposited over tens of millions of years on the Lomonosov ridge, just 250 kilometres from the North Pole. One study of the core revealed that a freshwater fern called Azolla grew abundantly in the Arctic Ocean for 800,000 years about 50 million years ago (Nature, vol 441, p 606). At the time the Arctic Ocean was largely isolated from other oceans, and fresh water from rivers would have floated on top of denser salt water. “It might have been, at least in the surface waters, one of the biggest lakes on the planet,” says Moran.
    Surprisingly warm

    The waters of this mega-lake were a surprisingly warm 10 °C, but that’s nothing to the temperatures reached a few million years earlier during the hottest part of the Eocene, when the ocean was salty. According to another study of the core the surface water 55 million years ago was around 18 °C, peaking at an incredible 23 °C – more than warm enough for a pleasant swim at the North Pole!
    The Arctic Ocean peaked at 23 °C, more than warm enough for a pleasant swim at the North Pole!

    What about the Antarctic? Here too gathering evidence is far from easy. Ice cores from Antarctica’s kilometres-thick ice sheets are no help, for even the oldest ice is a mere million years old. It’s the land beneath the ice that holds the secrets. “We don’t want the Antarctic ice sheet to disappear, for there is 67 metres of sea level stored there, but gosh, it would be lovely, from a palaeoclimate perspective, to know what’s under all that ice,” says Wilson. “In particular, because Antarctica has certainly been in a polar position back through the Cretaceous.”

    Fossil hunters on the mainland are limited to a few exposed sites. But on the Antarctic Peninsula, a finger of land that juts north towards South America, enough rock is exposed to give explorers a glimpse not just of Antarctica’s ancient flora and fauna, but of the nature of the seas around it.

    About 150 to 100 million years ago, the peninsula was a mountain range similar to the Andes, and its rivers drained into a massive basin, now called the James Ross basin. Over millions of years, the basin filled up with sediment and later the rocks it formed were uplifted. Today these rocks lie exposed on islands off the Antarctic Peninsula and contain a treasure trove of fossils from the Cretaceous, including silvery slivers of shells of ocean-dwelling ammonites and gastropods. In the late Antarctic summer, these fragments glint as they catch the sun which barely rises above the horizon. “It looks like the surface is covered in jewels,” says palaeoclimatologist Jane Francis of the University of Leeds, UK, a veteran of 12 expeditions to the poles.
    Ferns and cycads

    Besides ammonites and gastropods, Francis and her colleagues have found abundant fossils of sea urchins and lobsters that lived on the sea floor, shark teeth, and even massive marine reptiles with rib bones about half a metre long. Oxygen isotopes in the shell fragments show that the waters around Antarctica 100 million years ago were a balmy 15 °C, compared with -2 to 0 °C today.

    Dinosaur bones, which must have been washed down off the peninsula into the sea, have also been found in the marine sediments (see “Dinosaurs at the poles”). Plant fossils unearthed by Francis and her students show that 100 million years ago the peninsula was lush with ferns and cycads, along with conifers resembling the monkey puzzle tree. Analysis of the shape and size of fossil leaves has led Francis to conclude that the peninsula was very warm during the mid-Cretaceous, with a mean annual temperature of about 17 to 19 °C, similar to that of South Africa today. “That’s almost sub-tropical,” says Francis.

    Growth rings in one fossil tree trunk suggest trees thrived despite complete darkness in mid-winter. “In tree-ring terms, the tree was very happy, it wasn’t growing in any kind of stress, there’s no sign of frost rings and there’s no sign of drought,” Francis says.

    Her team has also found fossil flowers dating back to about 85 million years ago. These include flowers resembling those of Siparunaceae, tropical vines found in the Amazon, as well as those of the Australian eucalyptus and Winteraceae trees such as the Tasmanian mountain pepper.
    Sweltering greenhouse

    It’s abundantly clear that both the Arctic and the Antarctic were ice-free and warm from about 100 million to 40 million years ago. But until a decade ago, climate scientists struggled to explain how the Earth could have become so warm at the poles. Their models suggested it could only have happened if levels of carbon dioxide in the atmosphere were very high – turning the Earth into a sweltering greenhouse – but this would also have made the tropics extremely hot. Isotope ratios in marine shells, however, suggested that tropical waters were not much hotter than they are today.

    As it turns out, the models were right and the shell studies were flawed. Recent and more careful studies by Wilson and colleagues (Geology, vol 30, p 299) suggest that tropical seas were indeed hotter during the hothouse phase, with the surface waters being as warm as 34 °C compared with 29 °C today, says Raymond Pierrehumbert of the University of Chicago, a climate researcher and contributor to the RealClimate blog.

    Despite this advance, climate modellers face a new problem. While pumping up atmospheric levels of CO2 in the models creates ice-free poles and warmer tropical waters, the land in the tropics becomes unbearably hot. “The temperatures are so high that unless land plants behave differently from modern types, you would be beyond their temperature tolerance,” says Pierrehumbert. “We are talking of temperatures on land of an average of 40 °C, and with seasonal fluctuations they might even go up to 50 °C. It would kill off just about anything on land.” Today, annual mean temperatures rarely exceed 30°C.
    We’re talking average temperatures of 40 °C. That would kill off just about anything on land

    As outlandish as these simulations seem, the models might yet again prove to be right. Researchers such as Matthew Huber of Purdue University in West Lafayette, Indiana, have only recently begun to look for evidence of plant dieback in the tropics at this time. No one had thought to look before.
    Too cold

    There is yet another serious problem for climate modellers. The one place the models suggest did get cold during the hothouse episode is the interior of continents at high latitudes – regions like Siberia. This doesn’t fit with the evidence.

    In rocks from the late Cretaceous in Siberia, Robert Spicer of the Open University in Milton Keynes in the UK and his colleagues have found plenty of evidence for ferns and flowering plants, and even possibly the pollen of palm trees (Earth and Planetary Science Letters, vol 267, p 228). Their analysis suggests that at that time Siberia’s mean annual temperature was about 13 °C, rarely touching freezing even in the winter months. “All the climate models give you very, very cold continental interiors [at high latitudes] in the winter time, so cold that you would certainly freeze palm trees and kill them off,” Pierrehumbert says.

    One answer to this puzzle is to keep pumping up the CO2 levels. Models predict that the interiors of continents at high latitudes would not have frozen during the winter if CO2 levels were higher – but this means the tropics would have got even hotter.

    Huber has suggested a possible answer to this dilemma: what if much more heat from the tropics was somehow carried to the poles, keeping the tropics from boiling over. He and Ryan Sriver, also at Purdue, think they have found one possible mechanism.

    They studied conditions in tropical waters before and after the passage of present-day cyclones. They found that cyclones mix up the upper layers of oceans, moving heat downward. They argue that ocean currents then transport this heat towards the poles, reducing the temperature gradient between the tropics and the polar regions ( Nature, vol 447, p 577). Many researchers think the intensity, frequency and duration of tropical cyclones increase with higher temperatures. If so, the amount of heat transported to the poles by cyclones would increase greatly as temperatures rise. In a hurricane-ridden hothouse Earth, this could have kept the tropics below 35 °C, while the poles simmered in subtropical heat.

    However, Pierrehumbert thinks that the cyclonic heat-pump idea needs more work, and that explaining the warm interiors of continents remains a challenge. “This is now the most mysterious and toughest looking part of the problem,” he says.

    Others might beg to differ. A few lines of evidence point to something seemingly impossible: ice sheets during the warmest phase of the Cretaceous. “Nobody can imagine that we had these high temperatures and at the same time we had some large glaciers in the Antarctica,” says André Bornemann of the University of Leipzig in Germany. Indeed, models cannot replicate these conditions.

    One recent study by Bornemann’s team suggests that for a 200,000-year period around 91 million years ago, there were ice sheets at least half the size of the ones that blanket Antarctica today. The evidence comes from oxygen isotope ratios in shells from the Atlantic seabed ( Science, vol 319, p 189).

    However, a similar study by Wilson’s team found no evidence of glaciation ( Geology, vol 35, p 615), so this issue is far from settled. But if ice sheets can grow suddenly even during hothouse periods, Wilson point out, it means the climate can change more suddenly and dramatically than anyone thought. “That really demands being understood.”
    High volcanic activity

    Despite these vexing issues, there is a growing consensus that the hothouse climates were due to high levels of CO2 in the atmosphere. But where did it come from?

    Among other things, the amount of CO2 in the atmosphere depends on the balance between volcanic activity and the weathering of rocks. High volcanic activity during the Cretaceous might have kept the level of CO2 high, says Wilson. Later on, volcanic activity may have fallen and weathering increased as the Himalayas began to form, pushing Earth into an icehouse phase.

    However, while CO2 levels up to a million years ago can be directly measured from bubbles of air trapped in ice sheets, it’s much harder working out what they were 100 million years ago. Researchers have to rely on proxies such as the number of pores in fossil leaves, and there are still big uncertainties. Pinning down these numbers is critical, for this would tell us just how sensitive the climate is to rises in CO2.

    Some models suggest CO2 levels were 16 times as high as pre-industrial levels during the Cretaceous and Eocene hothouses, while others suggest eight times. Despite the uncertainties, eight times fits in far better with the proxy data, suggesting that the climate is highly sensitive to rises in CO2.

    This does not bode well for us, given the amounts of CO2 we are dumping into the atmosphere. CO2 levels look set to double from pre-industrial levels and if we keep failing to curb emissions, they could quadruple within 200 years. “Then we are half way towards the CO2 levels that turned the world into the Cretaceous hothouse,” says Pierrehumbert.
    Dinosaurs at the poles

    It is hard to believe that Antarctica once enjoyed a climate warmer than that of England today. Of all the images at odds with that of the frozen continent we know, the one of dinosaurs roaming lush forests is perhaps the most mind-boggling of all.Judd Case of Eastern Washington University in Cheney, Washington, and Jim Martin of the South Dakota School of Mines and Technology in Rapid City have been on many expeditions to hunt for fossils in the James Ross basin on the Antarctic Peninsula.They have analysed the remains of six kinds of dinosaurs, found by them and others, that date from 80 to 65 million years ago – the very end of the age of the dinosaurs.These include a dromaeosaur (a type of meat-eating velociraptor), a hadrosaur (a duck-billed dinosaur), hypsilophodontids (turkey-sized plant-eaters that moved about in herds), iguanodontids (herding dinosaurs that were ancestral to the duck-billed dinosaurs), and nodosaurs (short, squat creatures with armoured plating on their backs). The most impressive find has been the megalosaur, a 6-metre-high carnivore resembling T. rex.On the opposite side of the world, dinosaurs were also ranging around the Arctic Circle. Hypsilophodontids have been found in northern Alaska and hadrosaur bones have been discovered on Bylot Island near Greenland.Case points out that some of the dinosaurs living in Antarctica towards the end of the Cretaceous had already disappeared elsewhere. This is because flowering plants had colonised the warmest regions of the Earth, and dinosaurs had consequently evolved to adapt to the changing vegetation, but not in Antarctica. “It’s one of the last places to get flowering plant fauna,” says Case.The polar dinosaurs would also have had to adapt to long periods of light and darkness. The skull bones of hypsilophodontids suggest that they had large eye sockets, possibly to help with foraging during the dark – but warm – winter months. “There was plenty of greenery, even though it was dark,” says Case. “So there were lots of things for the dinosaurs to eat.”

  20. 70
    Ernst K says:

    Jathanon @46:

    “1. No ice on June 1, 2020
    2. Ice grows again during winter 2020-21
    3. Ice is at 1.7 on June 1, 2021
    4. Ice melts out maybe by July 1, 2021
    5. Ice grows again during winter 2021-22”

    The mistake you’re making is #4: “Ice melts out maybe by July 1, 2021”

    You are assuming that ice extent will melt at at least the same rate of km2/day will melt as currently melts in the high summer. However, there is a key difference: the ice that melts away in the summer of 2011 is much farther south than the new ice that forms in 2021 scenario.

    The new 2021 ice will be right by the north pole, which is colder and gets less solar radiation than the relatively tropical 70 to 75 deg N that melted so fast this summer. Therefore you can’t assume that it will met away at anything like 1.7 million km2/month.

    What these simulations are saying is that new ice will form at the pole in the first winter and persist throughout the first summer. From there it will grow each year until it catches up with ht ever-evolving equilibrium condition.

  21. 71
    Chris Korda says:

    I’m merely an engineer and certainly not a climate scientist but over the last few years I’ve been researching climate change and related subjects obsessively, including reading at least half the books listed in RC’s “Our Books” section, along with many other sources. A couple of questions have been keeping me awake at night lately.

    1. Is the RC community familiar with Dan Miller? I was blown away by his presentation “A REALLY Inconvenient Truth.” He communicates very effectively through such vivid examples as a car hitting a brick wall at various speeds. He also explains why we’re not reacting to climate change quickly enough: climate change is too different from threats that humans have faced historically, as he memorably demonstrates by contrasting climate change with a lion on the savanna. His presentation is humorous in a dry dark way, but also serious and engaging. Everyone I’ve shown it to was strongly affected, including some hardened veteran scientists. Dan got tired of watered down facts, and believes that people have the right to know the truth about what’s going to happen to them. I agree. Is there something RC could do to help him?

    2.What is RC’s position regarding Peter Ward and his Medea hypothesis? Is he considered an outlier? I’m wading through his books now. He spends much time debunking the Gaia hypothesis, and I’m sympathetic since I always found it absurdly utopian and typical of 60s new-age thinking. On the other hand Medea handles Fermi’s paradox well, and fits the facts revealed by paleontology: periodic ultra-nasty extinctions dominated by sulphur-compatible bacteria. It seems perfectly rational to me that bacteria would recolonize earth every chance they get, and not surprising that they’ve done so in the past and could do so again sooner than we’d like. It’s a logical consequence of Stephen Jay Gould’s work, the notion that there’s no overall direction in evolution, no better or worse, just fitness (or lack thereof) for endlessly changing conditions.

    3. It seems that RC regularly provides a platform for denizens of the lunatic fringe. The reposting (#69) of the article “When crocodiles roamed the Arctic” is a case in point. The main page of features gas masks, gold prices, ads for colloidal silver, gun nut propaganda, and such amusing topics as “On the 10th anniversary of the fraud known as 9/11…” One of the article’s “related posts” is an Aug 18 article titled “Carbon Dioxide irrelevant in climate debate says MIT Scientist.” How does tolerating such teabagger nonsense further RC’s stated aim of providing “climate science from climate scientists”? Doesn’t it tend to undermine RC’s credibility? And if so, wouldn’t it make sense to simply ban users who repeatedly engage in such behavior?

    Sorry to wade into what is doubtless a controversial issue, but moderation must be more effective if RC is to retain its considerable value. Yes in theory RC doesn’t touch politics, but RC doesn’t exist in a vacuum either. Human society is currently undergoing a monumental and unprecedented convulsion, the outcome of which will largely determine the quantity and quality of life on earth for centuries. The economic and social forces that got us into this mess in first place are more powerful than ever and have much to gain (in the short term) from preventing serious discussion of the reality of climate change and its accelerating impacts. Of course many deniers are only unwitting tools of industry but that doesn’t mean they’re harmless or that giving them a platform doesn’t jeopardize RC’s purpose. A lunatic who falsely cries fire in a crowded theater does mortal harm even though he may believe he’s doing good.

  22. 72
  23. 73
    CM says:

    Chris Korda #71, re: croc(k) postings,

    Well, Prokaryotes did cut and paste his #69 from a loony-bin (and he chose one hell of an anniversary to link to a site peddling those particular conspiracy theories), but according to the attribution, the loony-bin in turn lifted it from the basically sane pages of New Scientist, and sane people are quoted.

    That apart, I share your feelings. Prokaryotes, from one reader to another, please stop posting stuff from crank sites and amateur eccentrics. Link to the legit source when you’ve got one, and if you haven’t got a legit source, don’t bother. Oh, and surely you don’t need to post the full text of a 3,000-word article to make your point, whatever it was.

  24. 74
    Eric Swanson says:

    RE # 52, Phil. points to the impact of the polarization of light reflected from a transparent media. I can’t disagree against that, however, the issue is the quantity of energy reflected from the surface, not whether or not the SW energy has been polarized. The Brewster angle for the ocean is 53 degrees from Nadir, which is less than the minimum from direct beam at the NP.

    Since apparently no one else found it worth comment, I must correct my post (# 48). The Terra satellite has an equator crossing at 10:30 AM local time, but the highest latitude is crossed 6 hours later in local time at 4:30 PM on the ground. That’s because the orbit crosses the equator from the north-northeast, thus the highest latitude is to the east of the equator crossing. Just shows the confusion which I mentioned. The following graphic shows the orbit tracks for 7 Sept 2011.

    Since the time is given in GMT, the crossing at 0 Lon happens to be almost the exact local time of day for every equatorial crossing and one can follow the track back in time to the north-northeast. The highest latitude in the Southern Hemisphere occurs at 4:30 AM on the ground.

  25. 75
    Jathanon says:

    Nick Barnes says:
    11 Sep 2011 at 3:28 AM


    1. No ice on June 1, 2020
    2. Ice grows again during winter 2020-21
    3. Ice is at 1.7 on June 1, 2021
    4. Ice melts out maybe by July 1, 2021
    5. Ice grows again during winter 2021-22

    Where do you get this? From reading the paper, what they do is remove all the ice on July 1, 2020 (not June). In September 2020 there is no ice. In September 2021 there is about 1.7 Mkm^2 of ice. In September 2022 there is about 4 Mkm^2. I’m reading those numbers from figure 1, which only has numbers for September. Where are you getting your numbers for June 1 2021 and July 1 2021? I see no such numbers in the paper.
    “sea ice was artificially removed at the beginning of June”, which is where I got June 1. I did, however, miss on the graph that it was for September sea ice extents, assuming it was for the perturbation date. It makes somewhat more sense.

    Re: Ernst K says:
    11 Sep 2011 at 11:39 PM
    I would expect first year ice of that amount to melt fairly rapidly in that situation. Melt of thicker ice currently occurs in the Arctic Basin — and I would not expect the ice to just sit perched at the pole with the gyre and weather systems acting on it, and tenuous or no land connections.

  26. 76
    Nick Gotts says:

    “I agree kind of hard to reconstruct the correct spot of the crocodile from 383 m years ago, judging from a single site.” – prokaryotes

    Very difficult, since crocodilians did not evolve until the late Triassic (the Triassic was approximately from 250Mya-200Mya). At 383 Mya, the first tetrapods had only “recently” (maybe a few million years earlier) crawled out onto land; the oldest known reptile fossil is Hylonomus, dated at 312 Mya.

  27. 77
    John McCormick says:

    RE # 30

    Eric, minor point: You said “Sure, then the sea-ice is covered with fresh snow in winter, the albedo is high”

    No winter albedo. No sunlight.

    John McCormick

  28. 78
    L. David Cooke says:

    Hey All,

    Just curious if anyone has attempted an experiment of placing a 2.2kg block of ice on a 2.2kg box of sand in a refrigerator at roughly 12 deg. C and blowing air at roughly 1m/s and @ roughly -5 deg. C across its surface to see how long it takes to melt completly. How about placing a heat lamp over the top of the ice so that rough 2.5watts/m^2 are detected on the same ice, to see how long it takes to melt…?

    Has anyone tried repeating the experiments with the air at -1 deg. C, or place the heat lamp so that you can detect 5watts/m^2 at its surface to note the change in melt times.

    Has anyone tried the same experiments in slightly saline water? The point is, neither air temperature or direct IR from CO2 is likely the culprit.

    It is quite clear that the two greatest influences are simple synoptics associated with changes in atmospheric heat content affecting both aerosol/cloud content and warm ocean currents penetrating further into the Arctic Region.

    So what changes cloud cover, 134ppm of CO2, 200 Dobson units of Ozone, or 50Gt of fine ash particles from lower latitudes. Could it be the 0.7 deg. C warming of the atmosphere at an average altitude of 4km? Maybe it is simply a atmosphere in a synoptic phase of extremes that was common 10kya. To my knowledge the largest global change between 10kya and 7.5kya was the greening of the planet. To my knowledge the biggest change to the p.anet since the early 1800s and today was the denuding of the planet. The removal of at least 1/2 or 90Gt of uptake capacity or nearly twice the emmissions of fossil fuels since 1800 has more to do with the changes we see then the change in C12-13 isotope levels. Combined with changes in both soil moisture and aquafir levels is significant, why is this not part of this discussion?

    Dave Cooke

  29. 79
    Chris R says:

    #47, Pete Dunkelberg,

    I second your request for informed debate; informed by people reading the paper at hand.

    It has been claimed that this is a model study, and as models are clearly failing to reproduce the observed sea-ice trends in the Arctic, the study can be dismissed. This is not correct.

    Whilst one may disagree with the timescale to seasonally sea-ice free state implied by Tietsche et al (I for one do). The process outlined, loss of energy into the atmosphere and thence a) radiation to space, b) reduced inward atmospheric heat flux (figure 3b of Tietsche), is happening now in the Arctic atmosphere. OK, it’ll be happening in the next few months, for yet another year.

    For example, figure 4 of Overland & Wang shows a lower troposphere warming centred on the area of open water at the end of the melt season during the period October to December. This is observed in NCEP/NCAR reanalysis together with a substantial impact on geopotential height anomalies (Overland & Wang figure 6).

    Compare these observations with figure 3 of Tietsche et al; where it is seen that during the period of recovery there are large negative (outgoing) fluxes of longwave radiation, and sensible (that which can be sensed) and latent heat. The latter alone implies disturbance to the atmospheric column as shown in Overland & Wang figure 6.

    Overland & Wang
    “Large scale atmospheric ciculation changes are associated with the recent loss of Arctic sea-ice.”

  30. 80
    Edward Greisch says:

    RC made the NYT Dotearth blog again at:
    1 Mac and 4 wmar made outrageous comments there.

  31. 81
    prokaryotes says:

    German Physicists: Historic Low Arctic Ice is a “Consequence of Man-Made Global Warming with Global Consequences”

  32. 82
    prokaryotes says:

    Nick Gotts “Very difficult, since crocodilians did not evolve until the late Triassic”

    “Tiktaalik generally had the characteristics of a lobe-finned fish, but with front fins featuring arm-like skeletal structures more akin to a crocodile, including a shoulder, elbow, and wrist. The fossil discovered in 2004 did not include the rear fins and tail. It had rows[12] of sharp teeth of a predator fish, and its neck was able to move independently of its body, which is not possible in other fish. The animal also had a flat skull resembling a crocodile’s”

    The Fram Formation is a Late Devonian sequence of rock strata on Ellesmere Island that came into prominence in 2006 with the discovery in its rocks of examples of the transitional fossil, Tiktaalik, a sarcopterygian or lobe-finned fish showing many tetrapod characteristics. The Fram Formation is a Middle to Upper (Late) Devonian clastic wedge forming an extensive continental facies consisting of sediments derived from deposits laid down in braided stream systems that formed some 375 million years ago,[1] at a time when the North American craton (“Laurentia”) was straddling the equator.

  33. 83
    J Bowers says:

    Re. 80 Esward Greisch.

    I see Goddard got invited over by Revkin, too. Apparently, multiyear Arctic sea ice is recovering so the evil cabal has switched to sea ice area. Wow, that’s some recovery. “Remove the stitches nurse, the patient’s head is sure to stay attached this time.”

  34. 84
    Jbar says:

    Criminy prokaryotes, I thought 69 was supposed to be fun!

  35. 85
    Philippe Chantreau says:

    Prokaryotes, your own quote says that Tiktaalik was a fish, from a region that straddled the equator.

  36. 86
    Hank Roberts says:

    > multiyear ice

    D’oh. After a record low like 2007 or 2011, _any_ ice that persists through the following several years will count as an increase over the starting low.

    I know someone pointed that out in 2008 replying to similar

  37. 87

    “After a record low like 2007 or 2011, _any_ ice that persists through the following several years will count as an increase over the starting low.”

    Yes. In Watts land, the ice is always recovering, but this is, dare I say, ‘the best of all possible recoveries.’

  38. 88
    David Horton says:

    Thought I was going mad following this thread. A lobe-finned fish skeleton is found. Someone describes it as “crocodile-like” referring to its tendency to walk with legs kinda horizontal, belly on ground; and to its presumed use of both water and water edge habitat. Nothing to do with crocodiles in an evolutionary or taxonomic sense (and long preceding them) just a kind of ecological analog to help people picture the behaviour and ecology of an extinct speces. But someone sees “crocodile” thinks “tropical crocodiles” in the Arctic and away we go on a wild lobe-fin chase. Ignoring all the misunderstanding about the species being referred to, and a complete lack of appreciation of continental drift, what on earth would an “ice free Arctic” several hundred million years ago have to do with the melt of the Arctic over a few decades now? Denialism is clutching at thinner and thinner straws.

  39. 89

    #89 prokaryotes, the MIT article nails almost completely the missing links explaining ice model failures, thanks for it and the Ellesmere pieces. Ice physics is said complex because they fail to predict its behavior while likely missing factors, I call them vectors, 5 of them, wind, current, tides,morphology (ice shapes in the wind and under water) and ice momentum, that is with respect to the ice only. Then there is the atmosphere and sea water, the latest crucial atmospheric component are “boundary layers” , their effects are huge, I study them closely, and of late they are vanishing along with the ice, the very isothermal micro layers above the sea act as a buffer and or cut off heat exchanges between sea and air, surface air may be -35 C but right above much warmer. These isothermal layers rise during summer, but when they dont drop there is rather a complex (because I don’t know what sea component does) heat exchange at the interface of water and air which melts the ice further or stops it from forming. When the sea surface is warmer than the the air the exchange exacerbates the adiabatic lapse rate. Therefore its not surprising that the models fail, 4 times faster is a misnomer, the process of flushing is a matter of the vectors all moving in the same direction towards the North Atlantic. There could have been no ice at the North Pole this summer, but the vectors were diverging in all directions quite irregularly but often overall more North Atlantic bound in synergy than during the summer of 2010. I suspect the thermal signature of the ocean, its weighted equivalent temperature, at or near sea surface being also quite critical.

  40. 90
    Pete Dunkelberg says:

    David Horton @ 88, granted Tiktaalik is a red herring. But more than one comment above is floundering, including yours if you think Prokaryotes is a denier. ;)

  41. 91
    Tad Boyd says:

    Would it be fair to say that the low ice extents from 2008-2011 are really the same low ice extent of 2007? I’ve seen reports of a new record low hit this year and I’m trying to determine if this is a new event or if this is really just current state of the 2007 ice loss which NASA attributed to ‘unusual winds’ ‘set up by an unusual pattern of atmospheric pressure that began at the beginning of this century’


    Also, a request for clarification on the following line from this report:

    ‘The scientists observed less perennial ice cover in March 2007 than ever before’

    When the report says ‘than ever before’, does it mean since 1979 like many of the posts here specify? or does it actually mean ‘than ever before’ which are two very different things. Thank you.

  42. 92
    dhogaza says:

    I’ve seen reports of a new record low hit this year and I’m trying to determine if this is a new event or if this is really just current state of the 2007 ice loss which NASA attributed to ‘unusual winds’ ‘set up by an unusual pattern of atmospheric pressure that began at the beginning of this century’

    The weather patterns this September have not been as amenable to compaction (blowing ice together) as in 2007, so, no.

    But before fully adapting the denialist spin on 2007 being “due to unusual winds, not global warming” consider asking yourself “why was the ice so thin and weak in 2007 that the wind could compact it to such an extent”.

  43. 93
    prokaryotes says:

    Tad Boyd, read this and look at the graphics(@link).

    Arctic sea ice has melted to a level not recorded since satellite observations started in 1972 – and almost certainly not experienced for at least 8,000 years, say polar scientists.

    Daily satellite sea-ice maps released by Bremen university physicistsshow that with a week’s more melt expected this year, the floating ice in the Arctic covered an area of 4.24 million square kilometres on 8 September. The previous one-day minimum was 4.27m sq km on 17 September 2007.

  44. 94
    Kevin O'Neill says:

    Tad #91 It would be fair to say they’re a continuation of the low extents seen in 2007, though volume losses have decreased even further. Volume in 2011 is down nearly 40% compared to 2007.

    I’m sure they mean since scientists have been studying the Arctic. Scientists believe that 45 to 50 MYA the arctic was ice free – of course they were unable to actually observe it. Append ‘in recorded human history.’ I.e. — The scientists observed less perennial ice cover in March 2007 than ever before in recorded human history.

  45. 95
    Tad Boyd says:

    Thanks Kevin and prokaryotes, I’ve been having a hard time quantifying “then ever before” in the NASA report (and other places similar terms have been used).

    dhogaza, I was referring to the NASA report at

    The report didn’t go into whether or not there was a global warming link though the study it was referring to may well have. It did say that the loss of thick, year-round sea ice cover during the previous 2 winters was the primary cause.

    I don’t think that Dr. Ngheim of NASA posts here at RealClimate but I know some NASA scientists do so was hoping to get clarification from as close to the source as I could on what ‘than ever before’ meant. You’d be suprised at how many family gatherings arctic ice comes up in conversations and none of us really knows what time period we are talking about when discussing the lowest ice extent ‘than ever before’

    Thanks again.

  46. 96
    wili says:

    NSIDC has a new report out, but they have not yet declared a new record minimum.

    But, as they say, the slight differences between the different centers because of their differing data gathering techniques does not significantly alter the larger picture:

    “While the University of Bremen and other data may show slightly different numbers, all of the data agree that Arctic sea ice is continuing its long-term decline. “

  47. 97
    CM says:

    Pete #90

    > … red herring … floundering …

    Not to carp, but you know, when your sole cue about someone is they’re sounding fishy, or talking cod‘s wallop, they can be hard to plaice, uh, place. And noone wants to be a sucker with so many sarcastic fringeheads around. Now, can we get back to the surf smelt, uh, I mean, the surface melt? :-)

  48. 98
    Tad Boyd says:

    #96 wili

    Thanks for posting that link wili. nsidc was specific about the time period they were speaking of:

    ‘In the last few days, the decline in Arctic sea ice extent has slowed. NSIDC data show Arctic sea ice extent currently at the second-lowest levels in the satellite record’

    I don’t yet know if ‘than ever before’ (from my post #91) equates to ‘since scientists have been studying the arctic’ or ‘in recorded human history’ or the more specific ‘in the satellite record’ But the NSIDC was very clear.

    A little further down in the NSIDC report and as you mentioned in your post wili:

    ‘Arctic sea ice is continuing its long-term decline’

    Brings up another question: ‘long-term decline’ – Could that also be since the satellite record began? or is that something like since the Northern Hemisphere Little Ice Age? Or maybe longer?

    I realize I could ask questions all day long so I’ll try to make this my last question for this topic. wili’s post and link were just too close to what I was trying to figure out, to not ask. Thanks.

  49. 99
    Tad Boyd says:

    #98 found the answer to my own question on the NSIDC site. Posting here so no-one will spin there wheels on it. Thanks.

    ‘Yes, the data show that Arctic sea ice really is in a state of ongoing decline. The reason we know this is because satellites offer us a long-term record’

    NSIDC considers the satellite record to be a long term record so hopefully I’m getting the context right in concluding that the long term decline means since we’ve been keeping track with satellites


  50. 100
    tamino says:

    There’s sufficient data from shipborne observations to be sure that the decline in Arctic sea ice is unique at least since the beginning of the 20th century. There’s sufficient evidence from paleoclimate indicators to say with confidence that the pressent low levels of sea ice are unique for at least several thousand years.