Our research has shown that assessments of Greenland reflectivity change based on MODIS data are problematic. We have looked for darkening trends with MODIS and statistically speaking, we find a hint but nothing definitive. The image shown mentions darkening in 2011 relative to a six-year climatology, but does not mention the significant interannual variability of Greenland's albedo. Nevertheless, the work is suggestive of a trend which we expect to see someday, that is, temperature->snow metamorphism->albedo->temperature feedback. However, precipitation (fresh snow) could simultaneously increase and damp or overwhelm this signal. As to the long term trend of Greenland-wide albedo, the more trustworthy data are from CERES not MODIS (MODIS is better for hi-res. spatial patterns than for absolute albedo, because of problems retrieving snow albedo at large solar zenith angles such as are the norm in Greenland). Disclaimer: the MODIS surface reflectance team may disagree (to put it mildly) with these opinions.
Wang, X., and C. S. Zender (2010), MODIS snow albedo bias at high solar zenith angle relative to theory and to in situ observations in Greenland, Rem. Sens. Environ., 114(3), 563-575, doi:10.1016/j.rse. 2009.10.014. Wang, X., and C. S. Zender (2010), Constraining MODIS snow albedo at large solar zenith angles: Implications for the surface energy budget in Greenland, J. Geophys. Res. Earth Surf., 115, F04015, doi: 10.1029/2009JF001436. On Jan 10, 7:54 pm, Veli Albert Kallio <albert_kal...@hotmail.com> wrote: > Whitening of Greenland's snow cover is a new potential geoengineering target > that we haven't discussed. Greenland Ice Sheet has been discovered darkening > in 2011 with a new positive feedback in as > follows:http://eoimages.gsfc.nasa.gov/images/imagerecords/76000/76916/greenla... > > It is very remarkable that this darkening has occurred since 2000-2006 and in > some areas it is ~20%. > > Micromechanics of the snow cover darkening is explained here (analogous to > snow crystals in the > sky):http://earthobservatory.nasa.gov/IOTD/view.php?id=76916&src=fb -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
