A new study, independent of the Dark Snow Project, validates our hypothesis, that black carbon can accelerate Greenland Ice sheet melt.
The study, in Proceedings to the National Academy of Sciences (Keegan et al. 2014) finds that black carbon from wildfires facilitated widespread Greenland ice sheet surface melting in just two years since the end of the 19th century: 1889 and 2012. They argue convincingly that not just warm temperatures, but the positive feedback with black carbon and surface solar heating can push the surface energy balance into net heating and ice melt. Further, the likelihood for future increases in air temperature and wildfire boosts the probability of high altitude former “dry snow area” surface melting by end of century to every few years, if not even more frequently, they conclude.
Dark Snow Project
The Dark Snow Project’s first goal was sampling of the 2012 summer melt layer to answer if and by how much black carbon from wildfire and industrial sources played an important role in the widespread 2012 July surface melting of the Greenland ice sheet.
After a successful crowd funding campaign, on 8 July, 2013 at the southern Greenland ice sheet topographic divide, we extracted several snow/ice cores through the 2012 melt layer as part of ‘lean and mean’ helicopter mission. Frozen samples were then transported to the Snow Optic Laboratory at NASA’s Jet Propulsion Laboratory where McKenzie Skiles, present at the coring, painstakingly measured the black carbon concentrations.
We find black carbon concentrations equivalent with the peak values in Keegan et al. (2104), around 14 parts per billion (equivalent with nano grams per gram). We had 3 samples with concentrations above 12 ppb.
Our first results, described at the Dec. 2013 AGU meeting implied, as Keegan et al. (2014) confirm, that the cumulative effect of small absolute black carbon concentrations can produce sufficient increases in absorbed sunlight to enable surface melting.
In 2012, after publishing a measurement of the Greenland ice sheet albedo feedback, that did not explicitly include black carbon, as my home state of Colorado underwent record setting wildfires, I realized there was more to the story…
Where there is fire, there is smoke!
Sifting through data from NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) revealed smoke clouds near, over, and even in contact with Greenland.
The science Continues
We’re gearing up for a June-August 2014 intensive field campaign designed to further this science. In addition to continued investigation of black carbon, we are bringing new focus to analyze the darkening effect of microbes. Glacier and ice sheet biologist Dr. Marek Stibal will be gathering data on the increasingly pronounced effects of microbial and algal growth on the warming ice sheet.
As larger and larger ares of Greenland become subject to summer melt, more liquid water, a key limiting factor for microbial growth, is available on the ice sheet. In addition, Dr. Stibal and Dr. Karen Cameron will be examining whether fertilizing factors, such as nitrous oxide from industrial processes, may be encouraging additional biological activity on the ice sheet.
In a recent Dark Snow posting, Dr. Stibal noted that organisms on the ice produce dark pigments to shield themselves from intense sun, as well as other functions.
it is a sunscreen, a protection against the harmful UV radiation and also excessive visible radiation which can inhibit photosynthesis in the cells. But that’s not all. The pigment may also represent a sink for surplus energy that cannot be invested in cells due to limitations in temperature or nutrient availability, and may even act as a chemical defense against grazers as, for example, phenolic compounds in marine kelp. So, given the nuisances you have to put up with as an alga living on the surface of an ice sheet, it seems like a very useful thing to have.
Recent published science makes ever clearer that sea level rise from melting ice sheets will become a critical impact of climate change sooner than was imagined just a few years ago. In that light, the continuing research of Dark Snow Project to quantify additional contributing factors has never been more important.
- Box, J. E., X. Fettweis, J.C. Stroeve, M. Tedesco, D.K. Hall, and K. Steffen. 2012. Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839. doi:10.5194/tc-6-821-2012
Doherty, S. J., T. C. Grenfell, S. Forsström, D. L. Hegg, R. E. Brandt, and S. G. Warren. 2013. Observed vertical redistribution of black carbon and other insoluble light-absorbing particles in melting snow, J. Geophys. Res. Atmos., 118, 5553–5569, doi:10.1002/jgrd.50235.
- Mack, M. C., M. S. Bret-Harte, T. N. Hollingsworth, R. R. Jandt, E. A. G. Schuur, G. R. Shaver, and D. L. Verbyla. 2011. Carbon loss from an unprecedented Arctic tundra wildfire. Nature 475:489–492. doi:10.1038/nature10283
- Keegan, K.M., M.R. Albert, J.R. McConnell, and I. Baker. 2014. Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet, Proceedings to the National Academy of Sciences, May 19, 2014, www.pnas.org/cgi/doi/10.1073/pnas.1405397111