A new study by Polashenski and others find that “Neither dust nor black carbon causing apparent albedo decline in Greenland’s dry snow zone; implications for MODIS C5 surface reflectance“.
Just one point of their work I expand on here is the issue of declining MODIS Terra sensor sensitivity (Wang and others 2012; Lyapustin et al. (2014). First, Polashenski and others (2015) develop the MODIS albedo decline issue nicely. Now, rewinding back to early 2012, after becoming aware of Wang and others (2012) results, I evaluated whether the albedo decline was present in the completely independent Greenland Climate Network (GC-Net) data after Steffen and others (1996). In 2012, I wrote:
“Degrading MODIS instrument sensitivity identified by Wang et al. (2012) introduces the possibility that the declining albedo trends may be erroneous. To validate the MODIS albedo trends, coinciding observations from GC-Net AWS are examined. The ground truth data are situated across a range of elevations, spanning the ablation and accumulation areas. Analysis of the GC-Net data confirms declining albedo trends in the 2000–2010 period to be widespread in individual months from May–September. Trend statistics are computed where at least 7 yr of annual data are available from both GC-Net and MODIS Terra. Significance is designated here more strictly where the trend measured by the linear regression slope has a magnitude that exceeds 2 of the residuals from the regression. In 41 of 43 (95 %) of monthly cases May–September, the trend is found to be significant and decreasing (Table 1). In 10 of 14 (71 %) cases, for which both GC-Net and MOD10A1 trends are significant, the GC-Net declining trend is larger than the MOD10A1 trend. It therefore does not seem that MODIS sensor degradation is enhancing an existing trend.” – Box and others (2012)
Still, an update after 2010 is in order. Now, the evaluation through 2014 yields that there is still a real albedo decline for the southern part of the ice sheet, including places like Saddle or South Dome where surface melting is uncommon. Note how not only do both GC-Net and MODIS MOD10A1 show a decline, they share peaks and troughs. Given that the ground data having a footprint size of just a few square meters and the satellite data that have an effective footprint size of 5 x 5 km and that they pick up the same high and low years is impressive.
Wonk Alert: Still the bias is very likely a latitude-dependent. Notice how the GC-Net trend is even stronger than the MODIS trend in the far south (South Dome and Saddle). Consider that we have sunlight reflecting off of a highly reflective part (an ice sheet) of a sphereoid (the earth) that arcs more than 20 degrees north south. Snow and ice have reflectance depending strongly on viewing and illumination angles. So, the satellite data compensation for simple albedo are susceptible to amplification of small sensor degradation biases.
Let me add that the detected bias is smaller than the type of anomalies produced by for example the large July 2015 melting for NW Greenland. The red and yellow areas below are real local albedo anomalies due primarily to melting.
MODIS having a more negative trend than the ground data for the northern high and usually dry bright snow interior sites (See NASA-E, Tunu-N, Humboldt above) is also a real issue that Polashenski and others (2015) nicely report. While the bias we are looking forward to be compensated in the version 6 MODIS data (Lyapustin and othes 2014). As to the role of black carbon in Greenland’s albedo decline, I would say there is more to the story than what Polashenski and others (2015) report. Stay tuned.
- 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
- Lyapustin, A., Wang, Y., Xiong, X., Meister, G., Platnick, S., Levy, R., Franz, B., Korkin, S., Hilker, T., Tucker, J., Hall, F., Sellers, P., Wu, A., and Angal, A.: Scientific impact of MODIS C5 calibration degradation and C6+ improvements, Atmos. Meas. Tech., 7, 4353-4365, doi:10.5194/amt-7-4353-2014, 2014.
- Polashenski, C.M. J.E. Dibb, M.G. Flanner, J.Y. Chen, Z.R. Courville, A.M. Lai, J.J. Schauer, M.M. Shafer and M. Bergin, 2015, Neither dust nor black carbon causing apparent albedo decline in Greenland’s dry snow zone; implications for MODIS C5 surface reflectance, DOI: 10.1002/2015GL065912
- Steffen, K., Box, J. E., and AbdalatiW.: Greenland climate network: GCNet, US Army Cold Regions Reattach and Engineering (CRREL), CRREL Special Report, 98–103, 1996.
- Wang, D. D., Morton, D., Masek, J., Wu, A. A., Nagol, J., Xiong, X., Levy, R., Vermote, E., and Wolfe, R.: Impact of sensor degradation on the MODIS NDVI time series, Remote Sens. Environ., 119, 5561, 2012.
Sensors in Earth orbit give us the capability to monitor vast areas, daily, in near real-time. I’ve been working with daily NASA MODIS MOD14A1 data to map seasonal fire activity since the data begin year 2000. The map below illustrates the single most active day so far in 2015 for North America with fires ravaging central western Canada and interior Alaska.
A new strongest fire season?
Through 18 July, 2015, these data indicate the cumulative radiative power of North American fires to be the highest on record in the period of observations beginning in 2000. For July, 2015 fire power is 2.5 times the sixteen summer average 2000-2015. The fire season spikes above the annual average earlier in the year than in other years.
reporting from myyellowknifenow.com [29 June, 2015]:
Western Canada experienced more than 600 fires over the weekend, according to territorial authorities.
Canadian provinces and territories pool their firefighting resources in these circumstances. While the NWT has requested more backup, other provinces are perceived to have a “dire need” and are first in line.
“Saskatchewan, for instance, is undergoing a series of evacuations of communities,” said Frank Lepine, the territory’s associate director of forest management. “Manitoba is pretty close to that.
“The NWT will be receiving some single resources but no more crews at this time. [But] that may change by the end of the week.”
There are 129 fires burning in the NWT, which has experienced a total of 158 fires so far this season. The 20-year average is 66 fires for this time of year.
And the 2015 fire season is not yet over.
According to this analysis, the previous year 2014 ended by setting the annual record for cumulative fire power for North America. Year 2004 fires were concentrated around the Alaska Canada border.
Scanning past news stirs recent intense memories….
Canada’s Northwest Territories are on fire. The region is experiencing its hottest, driest summer in 50 years, and wildfire activity is more than six times the 25-year average. While blazes in sparsely populated northern Canada have a minimal impact on human safety and infrastructure, they have an outsized effect on the environment: The ancient, stunted boreal forests, or taiga, ringing the Arctic Circle contain 30 percent of the world’s land-based carbon.
July 2, 2004 — A pall of smoke the size of Texas continues to blanket most of Alaska, as several dozen wildfires continue to burn out of control. More than a million acres have burned in the state. There are currently 61 active fires in the state, mostly in the eastern interior
Alaska had a record warm summer with a statewide temperature of 4.6 degrees F (2.6 degrees C) above the 1971-2000 mean. May, June, July and August were all record breaking for the state.
Is the smoke drifting to Greenland?
Dark Snow Project has been busy gathering field data this summer in Greenland. We shall report on these. So, stay tuned!
Peter Sinclair is sitting in the cafe at the airstrip in Kangerlussuaq, the main port of entry for most folks coming in to Greenland. I believe this is the only place with daily, year round service from Europe – a single “Mothership” Airbus 330, making the run daily from Copenhagen. There’s a lot of patchy snow in the vicinity – forgot May is still pretty cold here, having come from blossom time in Scandanavia.
immediately ran into microbiologist Marek Stibal, who is already here camping not far away, taking sediment samples to flesh out the picture of biological activity on the ice.
In about 90 minutes I’ll take another hop to Ilulissat, site of a major Arctic conference next week, where I hope to catch up with a number of very active scientists. Jason Box is an organizer of the event, and we’ll join up in a few days.
My task this summer is to get as many interviews as possible, as well as shoot a lot of additional footage – and to that end, I’ll be staying in some visually stunning places – Ilulissat for one, and in a week, a place called Uummannaq.
More on this later, once I get settled in Ilulissat.
Building on our past experience, our work this summer is to continue flying UAV missions over Greenland ice, across an elevation profile to track the darkness of the bare ice area expanding as snowline climbs the ice sheet. Our UAV range this year is 4 times what it was last year, 200 km+! We’re flying higher end instruments over the ice dark ice fields, sheet’s blue lakes, river networks, moulins and crevasses, producing unprecedented visual and science material.
We’ve got two scientific papers in late stages of progress, finding that melt is amplified by not only fire activity but surface ice algae. Another surprising twist is to be released in a study nearing submission for publication in a top journal.
In a strong affirmation of the support from nearly 800 pledges, that has made possible Greenland expeditions in 2013 and 2014, we’ve secured funding for much of this year’s activity from a well known foundation who’s identity will may share soon.
What remains on our wish list for 2015…
- support for a Dark Snow videographer Peter Sinclair’s travel to an important Greenland climate science meeting 2-5 June and continue north to Uummannaq Polar Institute for interviews with Greenlanders, $3k
- A science tent to house our scientists at work, $1.8k
- each UAV flight is to have two video cameras on it recording 30 frames per sec to document the surface changes through time in better than HD resolution, $1.4k.
- after running our camp for 1 month on land, next to ice, 10 June – 7 July, it is advantageous to reposition the camp onto ice, following snowline inland on the ice sheet, to reoccupy at the same location as last year. For this we’re looking for another $12k for helicopter charter.
Your support has brought awareness of our science that was amplified by major network TV (HBO Vice, HBO Bill Maher, NBC Ann Curry, The Weather Channel, BBC, and more), print media (Rolling Stone) and online media (NASA, Outside, The Guardian, Slate, more than 50 news pieces).
Here’s our link to US tax deductible support using any normal credit/debit card hosted by PalPal.
Return supporters, on request, will receive a high quality decals. On request, pledges above $2.5 k will receive Greenlandic designed sun glasses.
Have an ice day!
the Dark Snow team
- Benning, L.G. A.M. Anesio, S. Lutz & M. Tranter, Biological impact on Greenland’s albedo, Nature Geoscience 7, 691 (2014) doi:10.1038/ngeo2260
- Doherty, S. J., T. C. Grenfell, S. Forsstro¨ m, 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.
- Dumont, M., E. Brun, G. Picard, M. Michou, Q. Libois, J-R. Petit, M. Geyer, S. Morin and B. Josse, Contribution of light-absorbing impurities in snow to Greenland’s darkening since 2009, Nature Geoscience, 8 June, 2014, DOI: 10.1038/NGEO2180