A cooling ice sheet would lose density, and if that is not accounted for in the GRACE measurements it would lead to an erroneous conclusion of a loss of mass, rather than a simple spreading of that mass over a larger volume.
Interesting, no?
...no.
First, any hypothetical temperature change at the surface will take decades if not centuries to propagate any significant depth into the ice sheet and cause a major change in depth.
Second, *mass* is what we care about, this is what GRACE measures regardless of the density of said mass. Mass is the total water stored (i.e. number of atoms) and thus can be related to the volume that goes into the ocean and the change in sea level if it melts. In your hypothetical scenario, a decrease in density will increase the height of the surface which will make the surface height measurements meaningless with regard to total mass.
Third, over the short term, the change in surface height will indeed be dominated by changes in snowfall (much much less dense than solid ice.) New snow typically has a density of around 100-200 kg/m^3. After it settles over an entire season it may have a density around 500-600kg/m^3. The ice in the greenland ice-sheet has a density closer to 1000kg/m^3. Thus, new snowfall on the surface will increase the height disproportionately with regard to mass. Please don't use the density of water/ice as your reference when the post you were replying to was referring to snow (which contains air between the snow flakes.)
Indeed the earlier post that you dismissed may have hit the nail on the head. Changes in density of the surface (firn) layer (possibly as a result of increases in snowfall) yield an apparent rise in surface elevation as seen by satellite altimeters such as used in the study you referenced, even while the
total mass is decreasing.
One of the predictions of climate change is an increase in the hydrologic cycle and thus more snowfall (warmer air holds more moisture which can yield more precipitation... in some areas, other areas less, lots of caveats here.)
Yep. Makes measuring a change in sea levels pretty darn hard, when the land and seabed are changing themselves! Throw in plate tectonics and it gets quite difficult to predict.
Which is why we correct for crustal deformation using GPS measurements and model based interpolations where necessary. It may not be perfect but it is far better than throwing our hands in the air and saying we'll never be able to measure sea level. It is complicated, but there is some damned fine work going on to make it as accurate as possible, and the scientific consensus is clear,
global sea level is rising, even if local sea level is falling at some locations.
ice growth above 1500 feet means almost nothing to global sea level
... it is the other way around. Ice growth at sea level (i.e. sea ice) has not impact on sea level because the ice is floating in the ocean, it is the same as if it were just water in the ocean. Ice growth above sea level takes water out of the ocean which decreases the volume of water in the ocean.
re: newspapers vs peer reviewed sources:
The ESA is a reputable organization and it is not a newspaper, but what you cited was more of a press release, not a peer reviewed publication, these have their place, but they must be treated with caution, especially when they are that old. The point of press releases is to get information out rapidly while waiting on the peer-reviewed article, so this late after the date there should be a peer reviewed article to cite.
The Australian journal appeared to be a newspaper, though it claimed to references a peer reviewed source, but no link was given, so there is no way to verify it. Please link to peer reviewed sources when possible, though newspaper links that include a reference to a peer-reviewed source are fine too. As a science writer myself, I can tell you that science writers get things wrong (not me, but you know, others
) So check the original science article when possible.
re: short time span of GRACE measurements
Regarding, a short GRACE time span, here is a more recent study of greenland using GRACE for the period 2002-2010 showing an
acceleration in mass loss over Greenland.
edit: ubb code
