WUWT readers surely remember all the media hype over this story. This was REP’s last entry on WUWT:
As WUWT readers are aware, there has been a great deal of attention paid by the main stream media to the extensive melt on the Greenland icecap that occurred during July (for example, see here, here, here, here, and here). The topic was addressed here at WUWT in two postings here and here. Anthony noted in the later posting that Andrew Revkin was almost alone in taking a more nuanced and skeptical view of the unprecedented nature of the event and has taken a fair amount of heat in comments for his effort.
And then there was the paper that showed that a shift in the jet stream caused warmer than normal temperatures in July 2012. Now a new paper in PNAS nails the trigger for the “insta-melt”, finding carbon soot combined with warmer temperatures was the trigger, not just in 2012, but also in 1889.
They get one attribution wrong, confusing climate change and weather events, but the science on the black carbon (BC) and albedo seems right. Their use of Oxygen 18 isotope records show that it was unusually warm in 1889 as well. They say in the Figure 2 caption:
…widespread melt events only occurred in 1889 and 2012. In C and E, melt occurred because of the deposition of high concentrations of BC and ammonium, indicating an albedo reduction due to BC from summer forest fires.
Visual evidence of carbon soot can be found in meltwater ponds in Greenland from this and other photos by James Balog, a real eye opener:
Image from National Geographic online slide show – Photo: James Balog – click for more
He writes:
In the winter a huge among of snow are accumulated on the Ice (2-3 meters, sometimes more) and we are not talking about 1 or 2 square-miles, it’s about 100.000′s of square miles (up to 1 million) on the Westside of the Ice cap and a similar picture on the Eastside… when the melting season starts in april-sep… the meltwater has to go somewhere, and for sure it goes downhill in huge meltwater rivers.
The black stuff on the bottom of the lakes is carbon dust and pollution in general… but not from one year, but several decades (the topographical conditions don’t change from year to year). On a flight over the Ice Cap a sky clear day, you can see hundreds of huge lakes with the black spot on the bottom.
The paper: http://www.pnas.org/content/111/22/7964.figures-only
Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet
Significance:
Through an examination of shallow ice cores covering a wide area of the Greenland Ice Sheet (GIS), we show that the same mechanism drove two widespread melt events that occurred over 100 years apart, in 1889 and 2012. We found that black carbon from forest fires and rising temperatures combined to cause both of these events, and that continued climate change may result in nearly annual melting of the surface of the GIS by the year 2100. In addition, a positive feedback mechanism may be set in motion whereby melt water is retained as refrozen ice layers within the snow pack, causing lower albedo and leaving the ice sheet surface even more susceptible to future melting.
Abstract
In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting.
Fig. 1.
Melt extent over the GIS determined from Oceansat-2 satellite scatterometer, Special Sensor Microwave Imager/Sounder, and Moderate-resolution Imaging Spectroradiometer satellite data for (A) July 8, 2012, and (B) July 12, 2012. Red areas indicate melt detected by the satellites, white areas indicate no melt, and blue represents ocean. The surface of almost the entire ice sheet, including the dry snow region, experienced melt on July 12, 2012. Figure courtesy of Dorothy Hall, NASA Goddard Space Flight Center.
Fig. 2.
(Lower) The annual average BC concentrations (ng g−1) from 1750 to 2010 of the Summit-2010 firn core and the 2012 surface section. (Upper) Sections of the BC record along with δ18O and ammonium records, plotted on a relative scale normalized to the maximum and minimum values in each record, for the time intervals (A) 1783–1788, (B) 1865–1870, (C) 1887–1892, and (D) 1905–1910, as well as (E) the normalized average value of BC and ammonium concentrations from the July 2012 surface sample, and approximate δ18O. These time intervals demonstrate extreme scenarios in the center of the GIS with (B−E) depicting the highest concentrations of BC, and (A) the warmest temperature since 1750, but widespread melt events only occurred in 1889 and 2012. In C and E, melt occurred because of the deposition of high concentrations of BC and ammonium, indicating an albedo reduction due to BC from summer forest fires. Importantly, these deposition events occurred during warm summers. In B, a high concentration of BC and presence of ammonium during a cooler summer suggest that the surface was below the energy threshold for melt. In D, the highest concentrations of BC and ammonium in the record were recorded during an average summer, suggesting that the BC was deposited at a time of the year when the available surface energy was well below the threshold for melt. The warmest temperature recorded in the core occurred in 1785, but widespread melting did not occur due to low BC concentration.
Tonyb says:
June 6, 2014 at 1:56 pm
I repeat my post from above:
Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet
Rubbish!
http://www.meltfactor.org/blog/?p=1240
See second photograph.
… boots on the ice offer a close look (and to sample) impurities concentrating at the surface. The fact is, much of this dark material is from cyanobacteria and blue-green algae. Photo J. Box.
Billy Liar – thanks! I was going to ask . . . did anyone actually sample and test this stuff? Or did they see the dark stuff at the bottom of the pool and assume they knew what it is?
Of course the Iceland volcanic eruptions could account for some melting. If the ice is covered with dust from the volcano it will not reflect the sunlight as well. This happened in the Austrian and Italian Alps in 1991, and that is how they found ‘Ortzi’ the mummified ice man. Anyway it will freeze up again soon.
Hi Pamela
I wouldn’t attribute the recent mega fires to climate change but to poor forest management ie smokey the bear. Burning off has not been carried out during the cool seasons in a sustainable way to reduce the fuel load your forests. So these mega fires are essentially caused by fuel loads building up in the forests fueling these massive mega fires. Australia has the same issue. Prior to European settlement in Oz the aboriginal people employed fire stick technology to keep fuel loads low in the eucalypt forests and to promote the growth of edible grass instead of woody species to feed their prey animals. Unfortunately the greenies in Oz are promoting this myth that if you don’t carry out fuel reduction burns the unburnt forests are suppose to become more fire retardant.
As far as I know, nothing out of the ordinary (never mind “unprecedented”) happened in Greenland in July 2012. The ice cap is still very much there. At most, surface melting was more extensive than usual, as it must be sometimes.
billy liar
Bit confused about your reference to me as I never said those words.
Many things contribute to arctic soot, man made and natural. Man made soot is fairly low hanging fruit that can be dealt with if it can be demonstrated it is a significant contributory factor to arctic ice melt. I don’t think its been proven yet but it strikes me as being worthy of research.
tonyb
Here are a few soot studies. See the first study from Hansen as well as the year. Then look at the last reference for CFCs, also from Hansen as well as the date. What he is saying is that most of the warming up to 2000 was driven by soot and CFCs!
—
Billy Liar’s blog reference says
How much is much? We know soot is up there in Greenland and much of the Arctic. Measurements of BC have been made dated back to over 3,000 years.
Nature – 28 May 2014
“Soot drives Greenland melting”
http://www.nature.com/nature/journal/v509/n7502/full/509537c.html
Even SkS has seen some light on this sooty issue.
http://www.skepticalscience.com/print.php?n=1804
In Oz we have some native trees that need fire to germinate seeds. Now botanists know that for a tree to evolve and adapt to this, requires millions of years to adjust. In the New England National parks rainforest patches, the Antarctic beech is dominant over eucalyps, and instead of being a deciduous tree as it is in other regions, it is like the gum trees, shedding leaves around the year. Trees do adapt to climate, but of course any Australian imported trees, like Oaks or wattles are not fire resistant etc., as are all deciduous trees. Gum trees of course like pines have oils in their leaves and needles and they burn very well. Too Well in bush fire regions. Pamela is correct, wild fires are not new, they occur from lightening strikes, and well before humans roamed these great forests. Unfortunately in Australia some human arsonists take great delight starting fires to destroy the bush, and any living thing that can’t escape.
When Keegan’s images are placed next to Greenland topography e.g. http://www.livescience.com/39298-under-the-greenland-ice-sheet.html, they still make no sense to me – soot or not.
Hi bushbunny
For anyone who wants to read a good reference on the subject I would recommend “The Biggest Estate on Earth How Aboriginals Made Australia” by Bill Gammage. It is well research book with 87 pages of reference notes if you want to go to the source documents.