NASA's Gravity Recovery and Climate Experiment (GRACE)
mission has been flying since 2002. GRACE measures fluctuations in Earth's gravitational field. These fluctuations are used to estimate ice loss (or gain) in Antarctica and Greenland.
asserts that ice loss is accelerating in Greenland and Antarctica. Yet, GRACE recorded a net gain of mass in Antarctica from 2002-2009. The "trick" is Glacial Isotactic Adjustment (GIA), also called Post Glacial Rebound (PGR).
The GIA correction used for the Antarctic and Greenland ice sheets respectively is 176 ±76 Gt/yr and 7 ± 19 Gt/yr. This correction represents the largest source of uncertainty in our ice mass estimate. However the GIA rate remains constant over the satellite’s lifetime, thus a change in the rate of ice mass-loss would not be contaminated by GIA errors.
Veligcogna asserts that Antarctic ice mass loss "increased from 104 Gt/yr in 2002–2006 to 246 Gt/yr in 2006-2009."
That means that from 2002-2006, GRACE was measuring a mass gain of 72 ±76 Gt/yr. Note: the error bar of the GIA is larger than the measured anomaly. From 2006 to 2009, GRACE recorded a net loss of 70 ±76 Gt/yr.
The steepening of the trend occurred in mid-2006. So there were 5.5 years of +72 Gt/yr and 3.5 years of -70 Gt/yr measurements. Velicogna didn't repeat the mistake she made in 2006
, when she actually published the pre-GIA (PGR) measurements...
Before the PGR (GIA) adjustment, GRACE indicated a gain in ice mass.
Now, there should be some PGR or GIA. However, PGR/GIA is model-derived. As yet, there aren't any sufficiently robust PGR/GIA measurements available.
But... Let's assume that the GIA/PGR adjustment is correct and ice mass loss did accelerate from 2002-2009. Where did the water go?
The rate of sea level rise has decelerated since 2002...
Where did the meltwater go?
More fun with numbers... Let’s assume that Antarctica is losing 190 Gt of ice mass per year. 190 Gt sounds like a really big number, doesn’t it?
360 Gt of ice melt will yield 1 mm of sea level rise. 190 Gt is good for ~0.5 mm/yr of sea level rise.
The volume of ice in the Antarctic ice cap is ~30,000,000 km3. 190 Gt is 0.0006% of 30 million km3. GRACE is measuring no net change in the ice mass; yet a 0.0006% annual change is being calculated from the PGR adjustment.
At 0.0006% per year, Antarctica will have lost 0.06% of its ice mass by the end of this century (99.94% of Antarctica will not have melted)! And sea level will have risen by… (drum roll)… 46 millimeters!!!… Almost 2 inches!!!