Archive for the ‘ice sheet melt factor’ Category
Surface reflectivity of sunlight is called “albedo”. Albedo is a Latin-based word referring to whiteness. The higher the albedo, the more sunlight can be reflected. As albedo decreases, more sunlight can be absorbed.
The absorption of sunlight is the largest single source of melt energy on the Greenland ice sheet.
Surface albedo across Greenland is mapped using data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) satellite-borne sensors. Before melting is underway, albedo is above 80%.
The NASA albedo data have an accuracy better than 5% (Stroeve et al. 2006; Box et al. 2012).
- Aerial oblique view of the lower elevations of the ice sheet in August 2005 from an area near the point of lowest reflectivity on the ice sheet. Photo J. Box
Impurities are composed of dust, algae, wildfire soot. Their relative importance to surface albedo remains incompletely understood.
As part of Dark Snow Project’s 2013 expedition, Dr. Marek Stibal gathers samples from an area of concentration near the darkest point on the Western Greenland ice sheet.
An increase in atmospheric heating of Greenland ice is a driver of Greenland ice albedo decline in summer, in part due to the expansion of bare ice areas, in part due to the heating effect on rounding ice crystals, and in part if the concentration of impurities increases.
In the period of high quality observations beginning early 2000, June 2013 albedo for the ice sheet is ranked 3rd lowest.
Greenland albedo started out very low in 2013 due to a snow drought exposing darker bare ice around the ice sheet periphery.
The albedo feedback with climate is responsible for doubling the temperature changes when climate warms or cools. This amplifier helps Earth’s climate system swing into and out of ice ages. The feedback is complex, including the effects of heating and light absorbing impurities, in a process that compounds through time.
Light absorbing impurities like black carbon from wildfire and industrial sources acts like a multiplier of the albedo feedback.
The Dark Snow Project aims to better understand the black carbon aspect of the albedo feedback through field data gathering and laboratory analysis.
Click here to visit the Dark Snow Youtube Channel.
- Box, J. E., X. Fettweis, J.C. Stroeve, M. Tedesco, D.K. Hall, and K. Steffen: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access
- Stroeve, J.C., Box, J.E., Haran, T., 2006: Evaluation of the MODIS (MOD10A1) daily snow albedo product over the Greenland ice sheet, Remote Sensing of Environment, 105(2), 155-171.
- Stibal, M. M. Šabacká, and J. Žárský, Biological processes on glacier and ice sheet surfaces, Nature Geoscience 5, 771–774, 2012, doi:10.1038/ngeo1611
As we landed in Greenland 24 June at the beginning of Dark Snow Project, the best laid plans lept out of reach.
Our helicopter was grounded by red tape.
Reacting, several phone calls produced a single flight with a different company. So, Dark Snow Project generated some field data already 25 June and we have another 12 days to work out a way to get back onto the ice sheet to gather more snow and ice samples to document the impact of light absorbing impurities on enhanced ice sheet solar heating.
“I never worked on a meticulously planned ambitious project that didn’t turn into an improvised as-you-go masterpiece.” – Dark Snow Project patron
Now, awaiting paperwork to push through Danish authorities [Don’t hold your breath. The Dane’s put a work firewall around their weekends], we are using our time productively, collaborating with journalists and scientists.
I’d reported on a highly abnormal snow drought that with more bare ground produced large negative albedo anomalies along west Greenland (Fig. 1).
Figure 1. Greenland reflectivity below 500 m elevation, including land areas. Notice the extreme low anomaly for 2013 that is by now erased.
Well, after about 4 months (1 Jun – 20 April) of that type of anomaly, the pendulum swung back late April, 2013, delivering a ~5 week return of snow showers that brought up to 300% of the normal snow for that period (Fig. 2) and relative cool weather (Fig. 3).
The snow drought is not actually ended everywhere. Along northeast Greenland, snow accumulation remains well below normal, 20% of normal for 1-Jan – 25 May. A @Promice_GL field workers had to transport from Zackenberg station to AP Oleson ice cap using a Argo track vehicle instead of snowmobiles.
Figure 3. Persistent cold for Greenland between 24 April and 19 May.
With the exception of melting 21-25 May, cold has been in place since 24 April. It’s clear now from the forecast for early June 2013 that temperatures will remain below freezing along much of west Greenland. It’s not extremely cold, just not yet melting much.
3 part study reconstructs Greenland ice sheet mass budget since 1840 and presents a theory connecting surface meltwater with ice deformational flowThursday, May 16th, 2013
Abstract . PDF (3210 KB)
J. Climate Editor Anthony J Broccoli deserves thanks for, presumably, working extra in recognition of critical timeline.
- Colgan, W., K. Steffen, W. McLamb, W. Abdalati, H. Rajaram, R. Motyka, T. Phillips, and R. Anderson, 2011a: An increase in crevasse extent, West Greenland: Hydrologic implications, Geophy. Res. Lett. 38, doi:10.1029/2011GL048491
- Cuffey, K.M. and W.S.B. Paterson (2010). The Physics of Glaciers, Fourth Edition. Elsevier, 693 pp.
- Motyka, R. J., L. Hunter, K. A. Echelmeyer, and C. Conner, 2003: Submarine melting at the terminus of a temperate tidewater glacier, LeConte Glacier, Alaska, U.S.A. Ann. Glaciol., 36, 57-65.
- Nick, F.M., A. Vieli, M.L. Andersen, I. Joughin, A. Payne, T.L. Edwards, F. Pattyn & R.S.W. van de Wal, 2013, Future sea-level rise from Greenland’s main outlet glaciers in a warming climate, Nature 497, 235–238 (09 May 2013) doi:10.1038/nature12068
- Pfeffer, W. and C. Bretherton, 1987: The effect of crevasses on the solar heating of a glacier surface, IAHS Publication, 170, 191-205.
- Phillips, T., H. Rajaram, and K. Steffen, 2010: Cryohydrologic warming: A potential mechanism for rapid thermal response of ice sheets, Geophys. Res. Lett., 37, L20503, doi:10.1029/2010GL044397.
- Phillips, T., W. Colgan, H. Rajaram and K. Steffen. Evaluation of cryo-hydrologic warming as an explanation for increased ice velocities near the equilibrium line, Southwest Greenland. J. Geophys. Res. ,2012JF002584, submitted 7 July 2012, revised 31 December 2012.