John Cook, Skeptical Science: Latest GRACE data on Greenland ice mass (from Wahr)

Latest GRACE data on Greenland ice mass

by John Cook, Skeptical Science, May 27, 2010

I don't plan to fall into the trap of breathlessly reporting every twist and turn of short-term climate fluctuations (I went through a bit of a silly period in March and April 2008). But we've been discussing Greenland trends, and as it's been over a year since posting GRACE data on Greenland ice mass, I figure we're due an update. Many thanks to Tenney Naumer of Climate Change: The Next Generation who emailed me the graph. Thanks also to John Wahr at the University of Colorado who analysed the GRACE data and granted permission to reproduce it here. Figure 1 below shows the latest satellite gravity measurements of the Greenland ice mass, through to February 2010.


Figure 1. Greenland ice mass anomaly (black). Orange line is quadratic fit (John Wahr).

This graph includes 12 months more data than Velicogna 2009 and shows the rate of ice mass loss is still increasing. Of course, this is only over an 8-year period. You get a broader picture when you combine GRACE data with other estimates of Greenland mass balance. Figure 2 combines altimetry, net accumulation/loss, and GRACE gravity data. It doesn't include GPS measurements, although this is consistent with other results, also showing acceleration in recent years.


 
Figure 2. Rate of ice loss from Greenland. Vertical lines indicate uncertainty, horizontal lines indicate averaging time. Blue circles are from altimetry, red squares are from net accumulation/loss and green triangles are from GRACE. The black line is a straight-line (constant acceleration) fit through the mass balance data for the period 1996–2008 with a slope of 21 gigatonnes/yr² (Jiang 2010).


What we find is, over a longer time period, Greenland was in approximate mass balance in the early 1990s. Before then, data are sparse, but GrIS may have been slightly increasing in mass during the mid-20th century.

Link:  http://www.skepticalscience.com/Latest-GRACE-data-on-Greenland-ice-mass.html#comments