The mystery of the melting Antarctic
Actually 3 mysteries in one.
The measurement of the actual amount of ice on land or at sea is extremely difficult. While we can measure the extent of the land cover very accurately the depth of the ice is very difficult to estimate. Complicating this is the possibility of snow cover which is not as dense as ice but adds to the difficulty in measuring the actual ice thickness and the amount of unfrozen water under the ice in rivers and lakes which does the same.
More complicated is the measurement at sea due to the difficulty in assessing ice edge boundaries and even more so when there are ice floes and packs with clear water in between. In the Arctic it is possible to get measurements by submarine and icebreakers to give some idea of depth
Conventional measurement depends on using multiple yearly measurements of extent and depth from multiple sources and combining the best estimates into a volume if ice with quite significant margins for error. The most inputs come from arctic ice measurement, and are represented by PIOMAS. A second measurement is done by Cryosat 2. The estimated volumes differ quite markedly at times.
In the Antarctic it is impossible to actually measure the depth accurately, hence a different method GRACE has been developed which works on estimating the gravitational differences detected by 2 satellites to determine the mass of ice above the land contributing to the gravitational fields. The volume of ice estimated in this way is potentially extremely inaccurate though not inexact as it is very dependent on the coefficient in the formula to give the volume of ice. A smidge up and there is more ice in Antarctica, a smidge down and there is less ice in Antarctica.
At different times using the gravitational measurement there have been suggestions of increasing ice volume in Antarctica but with further interpretation the GRACE measurements state that Antarctica is losing ice volume.
Hence the mystery. Antarctic sea ice has been increasing in the main for 30 years and is well above the average for the last 30 years. Ipso facto the Antarctic itself should have been definitely colder than normal in recent times. Hence there must be more not less ice in Antarctica.
Sea ice extent is dependent more on the coldness of the water rather than the air temperature itself, hence the second mystery. Measurements of the Antarctic water temperature claim that it has been warming over recent years. This should have resulted in less sea ice extent as predicted by IPCC models.
The third mystery is how has the Antarctic been losing ice volume. This is unexplainable by theory and fact. The Antarctic is too cold for the ice to melt and evaporate from the surface. The glaciers are not getting smaller and shrinking back in from the coast. This would involve less calving from the glaciers which would in turn be smaller. As demonstrated by the recent Spirit of Mawson expedition there is more not less ice along most of the coast of Antarctica.
If an adequate explanation cannot be given for how the ice is mysteriously disappearing from Antarctica then attention should be turned to the degree of accuracy of the GRACE measurements and a readjustment of the coefficient done to correct it to the reality of more ice volume in Antarctica.