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Not just ice albedo

Filed under: — rasmus @ 22 December 2006 - (Français)

A recent paper by Francis & Hunter provides an interesting discussion about reasons for the recent decline in the Arctic sea-ice extent, based on new satellite observations. One common proposition about sea ice is that it involves a positive feed-back because the ice affects the planetary albedo (how the planet reflects the sunlight back to space before the energy enters the ‘climate system’). Yet, there is more to the story, as the ice acts more-or-less like an insulating lid on top of the sea. There are subtle effects such as the planet losing more heat from the open sea than from ice-covered region (some of this heat is absorbed by the atmosphere, but climates over ice-covered regions are of more continental winter character: dry and cold). The oceanic heat loss depends of course on the sea surface temperature (SST). Open water also is a source of humidity, as opposed to sea-ice (because its cold, not because its dry), but the atmospheric humidity is also influenced by the moisture transport associated with the wind (moisture advection). Francis & Hunter found a positive correlation between lack of ice and the downward long-wave radiation, something they attributed primarily to cloudiness. Hence, clouds play a role, both in terms of influencing the albedo as well as trapping out-going heat. Francis & Hunter suggest that the changes in the long-wave radiation is stronger than the clouds’ modulation of the direct sunlight.

In the past (IPCC TAR), sea-ice models were notorious for difficulties in providing realistic description. Part of the problem, however, may also be the coupling between the ocean and the atmosphere component. I do not know if these aspects are improved in the upcoming IPCC report, however, Francis & Hunter propose several factors that may affect the sea ice edge position, such as oceanic influences, river discharge, non-linear effects, temperature advection and wind, and find that they play different roles in different locations.

The polar regions have white nights during summer with 24-hour sunshine (albeit at an angle) and 24-hour darkness during winter. The albedo feed-back of sea-ice can only be active during summer when there is sunlight to be reflected. The sea-ice extend also varies with seasons, with more open sea during summer and more ice covered area during winter. Furthermore, sea ice is pushed around by surface winds. Thus the effect of any change in the sea-ice extent may differ for different seasons. Less sea-ice during winter may cause more heat loss from open sea – however, at one point when the temperature drops sufficiently, ice will start to form again. Open sea may provide more favourable conditions for polar lows (storms). Cooling in the surface layer and mixing from wind exposure may furthermore affect oceanic currents and perhaps the deep water formation. During summer, the extra shortwave absorbtion is likely to dominate.

Another interesting question is: How does the loss of sea-ice affect the ‘planetary heat engine’, when more heat escapes from high northern latitudes? If heat loss in the Arctic is enhanced as sea-ice retreats and uncovers a sea surface with higher skin temperature? This may be more than compensated for by a reduction in the albedo locally, as well as increased heat transport in the ocean/atmosphere, or enhanced AGW. It is plausible that a ‘cloud-enhanced greenhouse effect’ in the Arctic may cancel part of the oceanic heat loss, and this effect is consistent with the findings of Francis & Hunter. Thus, enhanced cloudiness and associated increase in the downward long-wave radiation may act as an additional positive feed-back for the Arctic surface, in addition to the albedo-effect, whereas the additional heat loss acts like a negative feed-back. Although subtle, Francis & Hunter’s findings may have quite important implications for the planetary heat budget.

Sea-ice area from NSIDCPositive feed-back processes taking place on a local scale, may give rise to larger local variations. In addition to the effect of wind-driven sea-ice, such feed-backs may explain the large local temperature anomalies and large natural variations in the Arctic. Another aspect, that sometimes also gets neglected, is the fact that the polar regions represent fairly ‘small’ regions in terms of degrees of freedom. Furthermore, temperature fluctuations tend to be fairly coherent over large parts (there is an anti-correlation in the see-saw structure associated with the NAO, however). Thus, profiles of zonal mean values (the mean values of the measurements taken at a constant latitude ring around the planet) involves comparing long stretched areas near the equator to broad short regions near the poles (if the surface area is compensated for), but due to spatial correlation, this implies that the bands near the equator involve many more degrees of freedom than those near the poles. Such latitudinal profiles of zonal means are analogous to comparing mean values of different sample sizes (a bit like comparing daily values to monthly and annual means). The implication is that events such as the early century warming are not as significant as when the a warming of similar magnitude is seen in the zonal mean profile at lower latitudes.


72 Responses to “Not just ice albedo”

  1. 51
    Jim Cross says:

    Re #34, #50 Amending my previous posts

    My view is GCR theory is more related to explaining thousand year changes; however, I recognize others have extended it to try to account for most of recent warming.

    On the hand, I haven’t received any response to my #34 post about the reason the Ewing-Donn model fell into disfavor, aside from the sea depth issue.

    The thing that has somewhat mystified me about the glacial periods is: “Where did most of the snow/ice come from to form the glaciers?” Did it come from the warm tropics and temperate oceans as global temperatures fell? Ewing-Donn suggests it came from a relatively ice-free Arctic.

    Is there a model somebody has run with the Earth axial tilt changes cycling the Arctic from relatively warm, lesser ice periods leading to heavy snow in the higher latitudes with more ice, frozen, dry periods until the glacial maximum is reached? This seems to be the core part of the Ewing-Donn model.

    Or, is this simply not how it happened?

  2. 52
    gary says:

    The thing that has somewhat mystified me about the glacial periods is: “Where did most of the snow/ice come from to form the glaciers?”

    What is the possibility that an ice-free Arctic Ocean will bring about ocean effect snows, capable of spawning very intense bands of precipitation, which deposit at a rate of many inches of snow per hour?

    http://en.wikipedia.org/wiki/Lake_effect

    [Response: The oceans. But snowfall over the Laurentide region probably came from the Pacific sub-tropics/mid-latitudes with some transport from the Gulf of Mexico, rather than the Arctic. – gavin]

  3. 53
    shargash says:

    If GCRs were responsible for recent warming, wouldn’t atmospheric temperatures by altitude have a different profile than for AGW? And if the atmosphere doesn’t exhibit that profile, isn’t that a big problem for GCR-induced warming?

    [Response:If it were due to an increased level of solar activity, one might expect a heating of the upper stratosphere (the ozone depletion also plays a role, but closer to the tropopause). quite the opposite is oberved. There is also the point that any albedo-based amplification ought to be more effective on the day-side of the Earth, where there is sunlight. It’s would therefore be difficult to explain why, on global average, tendency is that night-time increases faster than the day-time temperature. But the real emporer’s cloths is the lack of trend in the GCR, and as far as I know, lack of trends in the cloudiness… It really should be op to the GCR-antagonists to present evidence for trends in these. -rasmus]

  4. 54
    Jim Cross says:

    #52 Gavin Comment

    Are you referring to some of the studies showing El Nino like conditions during the last Ice Age?

    http://www.earthinstitute.columbia.edu/news/story07_11_02.html

    [Response: No. It’s just a statement about where rain/snow falling in North America was generally evaporated. ENSO conditions may make some difference but I would expect my statement to be pretty close to true regardless. – gavin]

  5. 55
    Jim Cross says:

    #54 Gavin Comment

    Reading the qualifications in your remarks, I’m guessing that the topic of the source of ice age glacial ice hasn’t been studied much either because everyone thinks they already know the answer or maybe because it is hard to study.

    I have always thought the Arctic Ocean to have been mostly covered with ice through most of the last Ice Age, only to begin breaking up with the Holocene. At the same time, I found it hard to understand how the temperate and tropical zones with reduced atmospheric and ocean temperatures during the Ice Age could evaporate enough water to drive enough snow far to the North to form the glacial ice. Hence, the mystery for me about glacial ice.

  6. 56
    Joseph O'Sullivan says:

    #39 David Iles

    I understand what you are commenting about. Scientific writing can be very technical and the writing style, apart from the technicalities, can be dense and convoluted. Legal writers have the same habits. Some in the legal community favor the “plain english movement”.

    Its where the writing is only technical as it needs to be and the writing is in a clearer and simpler writing style. The goal is to make legal literature more accessible to the general public.

  7. 57

    Liked Rasmus explanation ln #39, because it brings up a clear fact that the Polar long nights in darkness have a huge amount of lower latitude advection, primarily because vast areas of heat sources overwhelm the smaller much colder Polar zones. I must add that since the Arctic has been largely warmer now a days, it does create a lower latitudinal warming feedback of sorts. Heat from advection lasts longer in the Arctic, reducing the size of cold air mass formations considerably, making in effect the South of the Arctic largely warmer for much longer periods of time, reducing once upon a time long bitterly cold winters, to occasional irregular “weekend” winters largely dominated by fall like conditions. One can see quite often much smaller cold air masses struggling to linger, this is a sure sign that warmer air is taking over the Northern hemisphere at quite a remarkable pace.

  8. 58
    Adrianne M says:

    Very interesting! I recommend reading http://www.1ocean-1climate.com, where you can find more data on the Arctic-sea ice extent.

  9. 59
    Thomas M says:

    I see very little information regarding the water cycle in the discussions. It seems that as global ocean temperatures rise and the water cycle increases the additional temperature transfer from surface to atmosphere would be very great – not to mention the extra convection. Again, it seems this would be a lagging but extremely powerful negative forcing. If there are specific links regarding this I would be very interested in learning more.

  10. 60

    Re “I see very little information regarding the water cycle in the discussions. It seems that as global ocean temperatures rise and the water cycle increases the additional temperature transfer from surface to atmosphere would be very great – not to mention the extra convection. Again, it seems this would be a lagging but extremely powerful negative forcing. If there are specific links regarding this I would be very interested in learning more.”

    I think any gain in cooling from evaporation would be countered by the increased greenhouse effect from having more water vapor in the air.

  11. 61
    david iles says:

    Thank you Rasmus for your clarification, it helps me understand. I have been reading here for a year or so and just try to get what I can out the posts and comments. I appreciate anything you can do to help me understand what you are saying. And I also see why you would want to use the language you have developed to communicate with others in the field because by the length of your explanation it is obvious that posts could become incredibly long if you had to describe every detail in more public terms.
    Thanks for your effort.

  12. 62
    Hank Roberts says:

    Re “Very interesting! I recommend reading …” — I don’t think I’d recommend that site for anything beyond the owner’s belief that war caused the climate to change. It’s an opinion.

  13. 63
    William Astley says:

    In reply to:
    1) “bottom line is: there is no systematic trend in GCR or other solar indices that can explain the warming over the past ~50 years. -rasmus”

    2) “everything in the GCR-idea and the recent warming hinges on whether there have (has been?) a trend in GCR or not. So far, the GCR-theory proponents have not offered any explanation for how GCR can cause a warming if there has been no trend in the GCR since 1952. -rasmus”

    In reply to 1): See figure 6 in the attached paper that shows there is close correlation between observed the global temperature anomalies, including the last 50 years, to the level and changes in the solar index “ak”.

    From that paper: “It has been noted that in the last century the correlation between sunspot number and geomagnetic activity has been steadily decreasing from – 0.76 in the period 1868-1890 to 0.35 in the period 1960-1982, … According to Echer et al (2004), the probable cause seems to be related to the double peak structure of geomagnetic activity. The second peak, related to high speed solar wind from coronal holes (my comment: For example coronal hole 254 that produced the Dec 16,2006 peak in solar wind, during a sun spot minimum, see attached link to Solar Observation Data), seems to have increased relative to the first one, related to sunspots (CMEs) but, as already mentioned, this type of solar activity is not accounted for by sunspot number. In figure 6 long-term variations in global temperature are compared to the long-term variations in geomagnetic activity as expressed by the ak-index (Nevanlinna and Kataga 2003). The correlation between the two quantities is 0.85 with p< 0.01." (For the years 1856 to 2000)

    2005 paper by Georgieva, Bianchi, & Kirov �Once again about global warming and solar activity�

    http://sait.oat.ts.astro.it/MSAIt760405/PDF/2005MmSAI..76..969G.pdf

    Solar Terrestrial Activity Report
    http://www.dxlc.com/solar/

    In reply to 2): From Fangqun Yu’s 2002 paper “Altitude variations of cosmic ray induced production of aerosols: Implications for global cloudiness and climate”

    “…Lockwood et al. (1999) have shown that from 1964 to 1996 the strength of the solar magnetic flux, shielding the earth from GCR, has increased by appox. 41% while GCR has decreased by approx 3.7%. The ion chamber measurements (Ahluwalia, 1997) also indicate that the sea level GCR intensity has decreased by 2% from 1979 to 1994. Then GCR intensity decrease is expected to be larger at higher altitudes in the troposphere. From the data available, we estimate that the decrease in GCR fluxes during the past two decades (1979-1999) is 1/3 to 1/2 of maximum variations during the last solar cycle.”

    If the above data is accepted, there is smoking gun evidence that GCR flux changes AND solar changes could be responsible for a PORTION of the recent observed global temperature change (1950 to 2005) in addition to a portion of the temperature changes observed for the period 1900 to 1950.

    The question as to what are the likely climatic mechanisms which could have enable GCR and solar activity changes over the last 100 years, to have likely caused a PORTION of the observed temperature changes in the last 100 years, will be addressed in the next comment.

    [Response:Thanks for your comment. I’m sorry, but I didn’t get the link to the paper to work. However, it’s still problematic that the direct measurements of the GCR do not show any trend, and if the solar index ‘ak’ shows a trend but not the others, then that may suggest that there are some inconsistencies between your indeces. Other indicators, such as 10.7cm flux do nto indicate any trend either. For more discussion on this, please see: Benestad, R.E. (2005) A review of the solar cycle length estimates GRL 32 L15714, doi:10.1029/2005GL023621, August 13. -rasmus]

  14. 64

    Re “From that paper: “It has been noted that in the last century the correlation between sunspot number and geomagnetic activity has been steadily decreasing from – 0.76 in the period 1868-1890 to 0.35 in the period 1960-1982, … ”

    This is a lot less impressive than it sounds. The coefficient of determination is the square of the correlation coefficient, so r = 0.35 means only 12% of the variance is accounted for.

  15. 65
    gary says:

    http://science.nasa.gov/headlines/y2006/21dec_cycle24.htm?list88679

    “Astronomers have been counting sunspots since the days of Galileo, watching solar activity rise and fall every 11 years. Curiously, four of the five biggest cycles on record have come in the past 50 years. “Cycle 24 should fit right into that pattern,” says Hathaway.”

  16. 66
  17. 67
    Steve Sadlov says:

    RE: # 57 – How do you account for what has been happening during the winters, in the mid latitude Western US, since, more or less, the late 1990s? That does not square with the mechanism you have described. Are Yukon and Alaskan cold air masses somehow exempted?

  18. 68
    Steve Sadlov says:

    RE: #66 – The data are from 22 Dec. There have been some (minor) changes in the sea ice pattern since then. Most notably, the Bering Sea ice edge has swiftly moved to the south southwest, and Hudson’s Bay has essentially completed its ice closure and will now remain ice bound until this summer’s melt ensues. One item of note – the necking of ice between Greenland and Iceland has been coming and going (changing with winds) – we might see closure there this season, especially if the pattern that was prevalent in October and November returns.

  19. 69
    Adrianne M says:

    RE #62: The thesis on climate change by naval war is
    based on the assumption that the term climate should
    be defined: as the continuation of the oceans by other
    means, as defined by the author in a letter to NATURE
    in 1992 (Vol. 360, p. 292), see:
    http://www.oceanclimate.de , right column.

  20. 70
    Urs Neu says:

    Re 63

    Trends in solar activity and Cosmic rays in the 1950-present interval depend on the time period chosen. While there is a positive trend from 1960 to 1990 there is a negetive trend since 1980 and no trend at all for the whole period since 1950. This is the case for any geomagnetic activity index, also for
    the Ap index which corresponds to the ak index used in the cited paper. The Ap data can be found on
    ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/INDICES/KP_AP/MONTHLY.DAT
    I was not able to reproduce the corresponding part of figure 6 in the cited paper.
    Even if there is a trend for some part of the time period, there should be an overall trend since the 1950ies to explain the temperature increase since that time. The 1977-2006 mean (last 30 years) of the Ap index is the same (in fact a touch lower) as the 1935-1965 mean.

  21. 71
    Hank Roberts says:

    Urs, you wrote “there should be an overall trend since the 1950ies to explain the temperature increase”

    Doesn’t that presume the mechanism, whatever it may be, acts with little or no time lag? There are so many possible correlations here — like the well established one between cosmic ray counts and murder and homicide rates — that it’s hard to figure out what’s connected to what and how.

    Suppose (speculating in the absence of any knowledge) that, say, the sun’s varying magnetic field exerts, say, a varying drag on the rotation of Earth’s core by interacting with Earth’s magnetic field — that might warm the planet, but the lag time for the heat to reach the surface would be considerable.

  22. 72
    Urs Neu says:

    Hank, of course you are right that there could be a time lag. But if there is one, it is highly probable that this time lag always exists because it is a charachteristic of the mechanisms. Thus you should find it in the data. This is the case e.g. for El Nino and global temperature, where there is a strong correlation and a time lag of about 5 months (that’s why we will see the effect of the current El Nino on global temperature mainly this year). However, I haven’t seen any evidence for a coherent time lag concerning any solar parameter, neither sun spots nor cosmic rays nor magnetic field etc, and neither on the short term nor on the long term.

    If there is a time lag of global temperature to changes in solar activity or the magnetic field of more than a few decades, this should be detectable in the time series since the Little Ice Age. However, there isn’t any. The proponents of the solar influence always present the ‘perfect’ match of solar parameters and temperature since the Little Ice Age, with supposed time lags of a few years.

    If there is no trend since 1950, and solar parameters should explain the recent temperature rise, there would have to be a time lag of at least 50 years. But if there is a time lag in the order of 50 years, we should see it in the data of the last few centuries somewhere, but we cannot see it. Of course theoretically there could be a time lag of a century or more so that we would see now the effects of the rise after 1700 or 1800. But you will have a hard time to find corresponding physical mechanisms and to find a forcing-reaction model which reproduces the temperature evolution of the last few centuries in that way. Maybe it is possible but there isn t any evidence, which makes it quite unlikely.


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