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Greenland meltdown

Filed under: — gavin @ 21 September 2011

After a record-breaking 2010 in terms of surface melt area in Greenland Tedesco et al, 2011, numbers from 2011 have been eagerly awaited. Marco Tedseco and his group have now just reported their results. This is unrelated to other Greenland meltdown this week that occurred at the launch of the new Times Atlas.

The melt index anomaly is the number of days with detectable surface melt compared to the baseline period of 1979-2010. The higher the number, the more melt days there were. While this did not match the record 2010 levels, depending on the analysis 2011 was either the 3rd or 6th year in the rankings.

Analysis of the surface mass balance via regional modelling demonstrates that there has been an increasing imbalance between snowfall and runoff over recent years, leading to a lowering of ice elevation, even in the absence of dynamical ice effects (which are also occurring, mostly near the ice sheet edge).



Figure 2. Regional model-based estimates of snowfall (orange), surface melt and runoff (yellow) and the net accumulation (Gt/yr) (blue) since 1958.

The estimated 2010 or 2011 surface mass imbalance (~300 Gt/yr) is comparable to the GRACE estimates of the total mass loss (which includes ice loss via dynamic effects such as the speeding up of outlet glaciers) of 248 ± 43 Gt/yr for the years 2005-2009 Chen et al, 2011. Data for 2010 and 2011 will thus be interesting to see.

While the accelerating mass loss from Greenland is of course a concern, the large exaggeration of that loss rate by Harper Collins in the press release for the 2011 edition of the Times Atlas was of course completely wrong. The publishers have issued a ‘clarification’, which doesn’t really clarify much (Update (Sep 22, 2011): The clarification has been clarified from the original statement). As discussed on the CRYOLIST listserv, the confusion came most likely from a confusion in definitions of what is the permanent ice sheet, and what are glaciers, with the ‘glaciers’ being either dropped from the Atlas entirely or colored brown (instead of white) (No-one that I have seen has posted the legend from the Atlas that gives the definition of the various shadings, though in the 1994 edition I have, glaciers are (unsurprisingly) white, not brown).

The Times is still claiming that it stands by its maps (Update: The new clarification no longer makes this claim). This is quite silly, and presumably reflects the fact that it would be very expensive to reprint all the atlases that may have already been printed. In case this isn’t already clear, there is simply no measure — neither thickness nor areal extent — by which Greenland can be said to have lost 15 % of its ice. As a letter written by a group of scientists from the Scott Polar Research Institute says, “Recent satellite images of Greenland make it clear that there are in fact still numerous glaciers and permanent ice cover where the new Times Atlas shows ice-free conditions and the emergence of new lands”.

The push back from glaciologists on this issue was a good example of how the science community can organise and provide corrections of high-profile mis-statements by non-scientists – by connecting directly with journalists, providing easy access to the real data, and tracking down the source of the confusion. In so doing it also provides an opportunity to give the real story – that change in Greenland and the rest of the Arctic is fast and accelerating.

Update: Here is a figure showing the preliminary GRACE results for Greenland for 2010 and the beginning of 2011. The anomaly in 2010 was huge, indicating perhaps a total loss of about 500 Gt/yr:



Figure 3. The upper panel shows estimated monthly mass anomalies over Greenland from 01-2003 through 07-2011 as in Velicogna (2009); the lower panel shows the detrended monthly data (blue), plus a monthly climatology from 2004 through 2009, highlighting the exceptional mass loss in 2010 (~500 Gt-H2O).

Further Update: A more detailed analysis from the Scott Polar Research Institute in the UK demonstrates quite clearly that the Times map is wrong, and inconsistent with all other ice sheets in the Atlas:



Figure 4. The new Times Atlas map (left) together with a mosaic of two satellite images taken in August 2011 (right). Also on the right are contours of ice thickness shown every 500m. The blue line is the 500m ice thickness contour which is the same as the outline on the Times Map. The red line is the 0m ice thickness contour which would be a better representation of the ice sheet than the blue line. The Times Map excludes all the ice between the red and blue lines. Furthermore, it excludes all the ice caps and glaciers that are not part of the main ice sheet, visible on the satellite image but not shown on the map. (SPRI).


References

  1. M. Tedesco, X. Fettweis, M.R. van den Broeke, R.S.W. van de Wal, C.J.P.P. Smeets, W.J. van de Berg, M.C. Serreze, and J.E. Box, "The role of albedo and accumulation in the 2010 melting record in Greenland", Environ. Res. Lett., vol. 6, pp. 014005, 2011. http://dx.doi.org/10.1088/1748-9326/6/1/014005
  2. J.L. Chen, C.R. Wilson, and B.D. Tapley, "Interannual variability of Greenland ice losses from satellite gravimetry", J. Geophys. Res., vol. 116, 2011. http://dx.doi.org/10.1029/2010JB007789
  3. I. Velicogna, "Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE", Geophysical Research Letters, vol. 36, 2009. http://dx.doi.org/10.1029/2009GL040222

109 Responses to “Greenland meltdown”

  1. 101
    t_p_hamilton says:

    J Bowers, the poles will always be colder than tropics because of the angle of the sunlight. The larger the incident angle, the more spread out the light.

    Captcha has my first name and middle initial!

  2. 102
    Patrick 027 says:

    Re 99 J Bowers – yes, the Earth has sufficient obliquity that the insolation at TOA is actually larger over the summer solstice pole than anywhere else. Without snow and ice, much could be absorbed – however, there is still scattering from air and clouds and absorption by ozone and water vapor, and the low angle of the sun above the horizon may tend to increase these (I think), other things being equal (although increased absorption within the troposphere wouldn’t necessarily cool the surface if the air is not stable). But the annual average solar heating will still be lower in the polar regions; with seasonal temperature modulation by oceans, the poles will still tend to be colder. If you have a large enough land mass in the polar region, maybe it could be different (?) (but it would then be even colder in the winter).

  3. 103
    Patrick 027 says:

    … and the water surface albedo tends to be higher with the sun closer to the horizon. (I’m not saying these effects would prevent solar heating from becoming larger than at the equator (I’m not sure offhand), but they would have some effect).

  4. 104
    EFS_Junior says:

    #99

    It’s still all about insolation.

    TSI/sin(theta) = area TSI passes through on ground divided by area TSI passes through in space (unity).

    Integrate over a day or a year, doesn’t matter, there’s always a moving bald spot (line actually), called the rim of the projected area where TSI/sin(0) = infinity, we normally call it dusk or dawn.

    That’s where the factor of four comes from in total TSI hitting the Earth, 4*pi*r^2/pi*r^2 = 4 (surface area/projected area).

    You’d need very strong poleward fluxes of atmospheric/oceanic heat transfer just to cancel out the insolation problem to begin with.

    There is much more heat flux entering at the Earth’s equator than could ever occur at the poles given Earth’s present axis tilt.

    What hypothetical situation do you envision where this would not be the case (e. g. polar to equatorial net heat flux)?

  5. 105
    J Bowers says:

    Thanks for the replies.

    What’s latched itself into my brain is how a fixed point on the equator spends half of its time in darkness, but if Earth were to be on a perfectly vertical axis (no tilt) I have this notion that the actual poles would receive some light 24/7. I know the equator in such a scenario would receive more light overall, but at the terminator between day and night sides, what’s hitting the equator should be exactly the same as what’s hitting the poles. When coupled with the stonkingly lower albedo in the Arctic sea and southern hemisphere if all sea ice were gone – I think much lower than the average in the tropics – it makes me imagine that that would equalise temperatures quite a bit. I think I just have to model it in 3D using maps stripped of all sea ice, and think of a way of measuring diffuse light as an average at different latitudes over the course of a day, which might be a quick proxy for albedo averages at different latitudes.

    Patrick, I looked into water specular albedo, and it seems to be pretty much negligible.

  6. 106
    Patrick 027 says:

    Re 105 J Bowers

    - water specular albedo: well it is small but it does increase with angle from vertical (I don’t know the value at a glancing angle offhand).

    - terminator – insolation doesn’t just go to zero at the halfway mark (from overhead sun to the middle of the dark hemisphere) only because:

    1:
    The sun is an object with nonzero size (larger than the Earth) and finite distance from the Earth, so one can find lines that are tangent to points just behind the halfway point that are also tangent to the sun. (half the disk of the sun is above the horizon (assuming flat terrain) when the center of the sun is at the horizon, although the center of the sun must be slightly below the horizon at the halfway point from ‘noon’ to ‘midnight’ at equinox or equator (‘noon’ and ‘midnight’ here defined by instantaneous alignments and thus differing from standardized time (see ‘Analemma’ in particular)) – not including effects of refraction (or gravitational lensing, etc.)

    2, also a role in 3:

    The atmosphere extends outward, intercepting some additional solar radiation, …

    2.
    …which it can bend toward the surface with an index of refraction just slightly larger than 1 (sunset is delayed, sunrise is early) (there’s also gravitational lensing but I don’t think that’s of great signficance in this context – though I haven’t checked (PS it would make the sun appear to be slightly larger than it actually is; refraction does the same type of thing to the Earth’s surface as seen from space).

    3.
    and the atmosphere also scatters radiation (twilight/dawn/dusk, and solar heating of the air above the surface when the surface is in the dark (night doesn’t fall, it rises from the surface and sinks back to the surface as sunrise approaches)). There is of course scattered solar radiation from the Moon (maybe a bigger factor just after the moon formed?) and planets and interplanetary dust. And energy in solar radiation absorbed in the upper atmosphere via chemical reactions (?) and/or (?) ionization(?) (I’m not sure offhand) can be released, including at night (I think the term is ‘airglow’ – for clarification, feel free to look it up) – some of that can be absorbed at the surface or within the troposphere.

    4.
    the surface has roughness (mountains, and for very small scale, tree tops, ocean waves, etc.) (PS I’ve read that there are a few points near one of the poles of the Moon that experience perpetual light.)

    Some of these things are bigger effects than others, but none of them are going to get you anything like the solar heating that can occur when the sun is relatively high above the horizon. With zero obliquity, polar solar insolation of zero is probably a good approximation, I think. (The annual average insolation at the poles increases with increasing obliquity; there is a point where it gets larger than at the equator, but we’re a long long way from that.)

  7. 107
    Patrick 027 says:

    … on airglow – well it’s not to much farther to go to discuss heat capacity and the greenhouse effect (the atmosphere emits day and night, etc.). Airglow is seperate from direct or scattered solar radiation; perhaps I shouldn’t have mentioned it above, then.

  8. 108
    Coldish says:

    Hi Gavin, At 42 you refer to ‘…the climate sensitivity which can be constrained independently of the models (i.e. via paleo-climate data)…’. Can you direct me to some material on the paleo-climatic constraints on c.s.? Thanks, Coldish

    [Response: Try Kohler et al (2010) (doi:10.1016/j.quascirev.2009.09.026 ) or Annan and Hargreaves (2006) (doi: 10.1029/2005GL025259). We discussed this here too. - gavin]

  9. 109
    Coldish says:

    Thanks, Gavin. Much appreciated.


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