Patches of snow and bare ice near the edge of the snowline provide an illustration of the difference in reflectivity between the two surfaces.
Credit
Clément Miège
PROVIDENCE, R.I. [Brown University] — In a finding that may help scientists better predict sea-level rise in a warming world, Brown University researchers have found an underappreciated factor that controls the rate at which Greenland’s ice sheet melts.
The research, published in the journal Science Advances, used satellite imagery to track the movement of the ice sheet’s snowline — the elevation above which the surface is snow-covered, and below which bare ice is exposed. The study showed that snowline elevation varied significantly from year to year, and that its variation exerted an outsized influence on the amount of solar radiation the ice sheet absorbed. Changes in snowline elevation from year to year explained more than half of the annual radiation variability on the ice sheet, the study found.
Ultimately, the amount of radiation the ice sheet absorbs determines the extent to which it melts.
“People who study alpine glaciers have recognized the importance of snowlines for years, but no one had explicitly studied them in Greenland before,” said Laurence C. Smith, a visiting fellow at the Institute at Brown for Environment and Society (IBES) and a study co-author. “This study shows for the first time that this simple partitioning between bare ice and snow matters more when it comes to melting than a whole host of other processes that receive more attention.”
The results have significant implications for predicting future sea-level rise, the researchers say. Meltwater from Greenland’s ice sheet is a large contributor to global sea levels, and this study shows that regional climate models used to predict future runoff often predict snowlines inaccurately.
“We found that models don’t reproduce snowlines very well, which adds an uncertainty to future projections,” said Jonathan C. Ryan, a postdoctoral researcher at Brown and the study’s lead author. “But now that we’ve shown how important the snowline effect is, and have some direct observations of snowline positions, hopefully we can improve these models going forward.”
The reason that the snowline is so important has to do with the difference in reflectivity between snow cover and bare ice. Snow is extremely bright and reflects back into the atmosphere the lion’s share of the sunlight it receives. Bare ice is much darker, and therefore reflects less radiation. Instead, more radiation is absorbed, which heats the ice and leads to melting. These processes have been well understood by scientists for years. What wasn’t known was the extent to which they play out on the Greenland ice sheet, and to what extent snowline migration might regulate melt from year to year.
Ryan says he first got an inkling of how important snowline movement might be while doing field work on the ice sheet. He and his colleagues were trying to record snowline positions with aerial drones. Each day, they flew their drones inland across the bare ice. When they reached the snowline, they recorded the position, turned their drones around and flew back. At one point during the field season, they had to stop flying for a few days because of high winds. When they got back to flying, they found something surprising.
“Suddenly the snowline was just gone,” Ryan said. “In a couple of days it had moved 30 kilometers or so up the ice sheet and was now out of the range of our drones. That was the first moment we thought we should investigate the effects of snowline movement on melt.”
For the study, Ryan and his colleagues used images from the MODIS instrument, an imaging spectroradiometer that flies aboard NASA’s Terra satellite. They were able to get a time series of snowline positions from 2001 to 2017. They could also measure the reflectivity of both the snow cover and bare ice.
The images confirmed a substantial movement of the snowline from season to season and from year to year — reaching a maximum elevation in 2012, a record year for ice sheet melt. There was also a substantial difference in reflectivity between the snow and ice. The snow reflected an average of about 79 percent of the radiation that struck it. The ice, meanwhile, reflected only between 45 and 57 percent. The snowline movement combined with the differences in reflectivity mean that snowline position plays a dominant role in controlling the ice sheet’s energy absorption. All told, 53 percent of year-to-year radiation variability can be explained by the position of snowline, the researchers found.
That 53 percent figure dwarfs other factors that the researchers investigated. For instance, the researchers thought that processes that make already-dark bare ice darker over time would play a large role in controlling energy absorption. Pooling water, dirt layers and algae growth can all darken bare ice, making it even less reflective. The study found that those factors did make a difference in energy absorption, just not nearly as much as previous research had assumed. It turned out that position of the snowline had a five-fold stronger influence on energy absorption than the darkening of bare ice itself.
“That’s a surprise because there’s been a lot of work lately on these ice-darkening processes,” Smith said. “It turns out that in this case, we were missing the elephant in the room, which is the snowline.”
Having established the importance of snowline in energy absorption — and ultimately in melting and runoff — the researchers wanted to see if regional climate models properly captured the effect of the snowline. That’s important because those models are used to predict future runoff from the Greenland ice sheet.
The researchers found that two leading models both fail to capture snowline elevation accurately. One model, known as MAR, set snowlines too high and was therefore likely overestimating runoff in high-melt years. The other model, known as RACMO, set the snowlines too low, meaning it likely underestimates future runoff in a warmer climate.
Given the importance of snowline position as revealed in this study, the researchers say it’s important the models get the snowline right.
“We’re collaborating now with the modelers, providing them with our observed snowlines,” Ryan said. “That gives them some ground truth they should be able to use to adjust their models. Now there’s something to aim for.”
The result of those improvements in modeling snowline, the researchers say, would be more accurate forecasts of Greenland’s future contributions to sea-level rise.
###
The research was funded by the NASA Cryosphere Program (NNX14AH93G). Other co-authors were Dirk van As, Sarah Cooley, Matthew Cooper, Lincoln Pitcher and Alun Hubbard.
From EurekAlert! Public Release: 6-Mar-2019
Wow. Observational data, no mention of CO2 as a driving factor, no claims that the factor with the largest effect is being driven by human activity at all. Color me impressed.
Yup, refreshingly not front-loaded with assumptions on human culpability, conclusions looking for confirmation.
Also at this point mentioning CO2 generally informs me that generally bad science lays within. It seems to be a rare paper that can separate CO2 the mundane trace gas from CO2 the Herald of the End Times, so refreshing I could read an article about ice reflectivity & not have a flagellating spiel about the Original Sin of Mankind.
[“Flagellating Spiel”? Very nice, but, weren’t they a British band from the 70’s? 🙂 -mod]
Mod, you’re thinking of Spinal Tap.
“People who study alpine glaciers have recognized the importance of snowlines for years, but no one had explicitly studied them in Greenland before
These processes have been well understood by scientists for years. What wasn’t known was the extent to which they play out on the Greenland ice sheet, and to what extent snowline migration might regulate melt from year to year.
That was the first moment we thought we should investigate the effects of snowline movement on melt.”
This project should never have been given funding. Nothing was learned and the underlying physics had all been discovered before. There is no reason why the Greenland glaciers woold act any differently than other glaciers. The authors freely admit this. Why climate models do not take this into account, is that they cant possibly mimic the underlying physics on a global scale and NEVER will.
Then they go further to claim potential predictive ability. How could they do that unless they were also able to predict the phenomenon that causes the snow line to shift? I had a similar thought as you did. What new discovery was made?
“We found that models don’t reproduce snowlines very well, which adds an uncertainty to future projections …”
Add one more to the ever-growing list of things “the models don’t reproduce very well”.
Is there anything they do reproduce very well, apart that is from the modeller’s prejudices? Or his paymaster’s?
Yeah …. they reproduce the CO2 data that is fed into them quite nicely. …. they call it the temperature record, …. but really it’s just the CO2 record renamed
Duuh! What do the models actually do?
Help obtain grant money of course
+10 …of course
I think I’ve found the key paragraph.
“We found that models don’t reproduce snowlines very well, which adds an uncertainty to future projections,” said Jonathan C. Ryan, a postdoctoral researcher at Brown and the study’s lead author. “But now that we’ve shown how important the snowline effect is, and have some direct observations of snowline positions, hopefully we can improve these models going forward.”
And if the improved models don’t show what they want to see???
Just asking
James Bull
Why do you assume bias before any bias is shown? They mention “a warming world”, isn’t it warming a bit?
They point to models doing a bad job of predicting the key factor in ice melt. That sounds admirably skeptical to me.
Well you have to start the push back somewhere. As the world gets colder and colder, the professionals will point to the failures of the Co2 models more and more. The smart rats will leave the sinking Co2 ship fast, leaving their followers to holding the bag.
The warmer the atmosphere, the more water is carried by it and therefore the more snow that lands on Greenland. The more snow in Greenland, the more sunlight is reflected back into space. Sounds like another one of those negative feedbacks, you know, the ones that we were told would be positive and lead to tipping points and runaway agw.
While sounding reasonable that specific humidity should increase as temperature does, atmospheric data show that atmospheric specific humidity has done so except at very low (near surface) altitudes. In the lower troposphere and stratosphere it has actually decreased since 1948. See https://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl or go to climate4you.com climate + clouds button.
Good. Now please explain the physics of how a warming world that is 70% covered by water can have a decreasing trend in humidity.
Easy. Eschenbach T storm mechanism. AKA Lindzen adaptive iris. More rainout and its sequelae.
Has not done so. Sorry.
“We’re collaborating now with the modelers, providing them with our observed snowlines,” Ryan said. “That gives them some ground truth they should be able to use to adjust their models. Now there’s something to aim for.”
Ground truth? TRUTH? We don’t need no stinkin’ truth!
Where’s the (grant) Money in that?!
So that lets the Chinese ‘soot’ emissions off the hook then? It has only 20% of the impact the models authors claimed for it. So yet another ‘carbon’ emission that was over estimated in its effect.
But that last sentence is curious: “It turned out that position of the snowline had a five-fold stronger influence on energy absorption than the darkening of bare ice itself.”
What about the inverse effect of the darkened surfaces on the snowline? There is a positive feedback occurring here; these exposed surfaces surely accelerate melting, which exposes even more dark surfaces. So it is a two-way relationship.
Snowlines are remarkable examples of “natural thermometers”. Better than treelines because they are “calibrated” by the melting point of water. But some care in the interpretation of this process is required, because the result of this “measurement” process itself has some effect on the temperatures.
But I wouldn’t let the Chinese (and Russians) off the hook, yet.
The fact there was no mention of how the snowline is moving currently tells me they didn’t find that to be a problem. Or that it has been moving opposite to what would be a problem.
If they had found the snowline was retreating substantially you can bet your ass it’d be broadcast across the scientific world like proof of alien life, or a breakthrough in fusion reactor research.
The AGW religion has many true believers, seeing what they’d deem bonafide demonstrable proof of their god would be no different than Christians discovering unambiguous proof of Jesus’ second coming.
Or maybe there was notable retreat but the team studying it are composed of not-hysterical charlatans. If AGW was genuine I’d rather the cool collected proper scientists were in charge of documenting it’s proofs, that’s for sure.
Sum Guy March 7, 2019 at 5:49 am
Their drones had been grounded due to… high winds. So the snow line moved maybe because the snow moved. Powdery snow can be blown away, I have seen in while living in the Northeast. Now can high winds over a few days move snow 30 kilometers?
michael
Yes, that was my understanding as well. Winds blowing from the right direction (basically perpendicular to the glacier edge) blew the snow back from the edge and exposed more ice. Winds from other directions may do the opposite.
If that is the case, then it would be pretty difficult to accurately predict when powerful storms will track past Greenland on a path that causes wind to blow in the right direction. I would think the storm tracks are not predictable. Is it a coincidence that this was 2012 when sea ice extent was likewise said to be lower to to unusual storms?
Models can determine probabilities very well in many cases. They can’t predict what will happen next with high certainty, however. Modelers who try their luck in Vegas get taken to the cleaners.
Wow! They’ve just discovered that snow reflects more radiation than ice. Who’d have thought?
Sounds like they’re having fun with their drones. Maybe they can fly over the spot where those WW2 planes were abandoned and are now covered in 100 meters of ice. Probably not a lot of ice melt in that part of Greenland for the last 70 years. Observational data beats models every day.
Wouldn’t it have been simpler and cheaper to use the data on the snowline that the Danish Meteorological Institute have been collecting for the last 20 years:
http://polarportal.dk/groenland/iskappens-overflade
Click the tab “snegraenser”
And, no, it hasn’t been changing much, and certainly not in a way that is worse-than-we-thought.
In short a prime case of me-too-science.
Just what do these “Scientists” learn in college? Do they have any, even a modicum of practical experience in their field of endeavor? As a teenager, 60 years ago, I noticed that from the right angle snow on the ground looked like a gazillion diamonds sparkling in every color of the rainbow. Reading to find out WHY, I learned that it was from crystal structure of the snowflakes reflecting the rays of sunlight. A few years later, while helping run a pipe from the windmill to the watering trough I asked “Why are we only burying the pipe a foot deep. Won’t it freeze in the winter?” My father told me “very rarely do we get a hard freeze before we have a decent snow cover. The blanket of snow cover will act as an insulator and the warmth of the ground will keep the pipe from freezing.”
Any person that has been out ice skating frequently has noticed that often the ice on a freshly frozen pond is as clear as glass and when looking straight down the ice looks black. Rarely does the ice ever appear as white as snow. Next time you get a good snow fall where the snow builds up on your roof and ice forms on the eves, look at that ice. It is dirty, when you can see the ice it is melting when the sun hits the ice, Many times you can even see water vapor rising like steam from the ice. However, where this ice is covered by bright, shiny, white snow the ice is not melting. Any snow that is melting on the roof (in the area below the snow cover and above the roof tile) melts, runs down the roof meets the ice at the eve and freezes, making the ice dam bigger. Git rid of the snow on the lower edge of the roof and the ice disappears.
Now, if I learned all of this, before high school, 60 years ago, again I ask, what are they learning in college if they do not know this and are researching, ice, snow, freeze lines, etc. and why did they think they just made a significant discovery? – Wasted education. My grandfather knew it 100 years ago.
They didn’t claim to discover that snow albedo is higher than ice albedo. They referenced that it was a well known fact. They stated that the snow line was found by observation to be more variable than expected and that models used to estimate melt rates were not doing a good job of estimating the snow line.
Oh, ok, so the snowline, which varies significantly affects the melting process. So sometimes it’s more, sometimes less. So what? SLR is just one more in the Alarmist’s arsenal of scary bedtime stories they like to tell. You know, to scare people. But it really is no big deal, despite their hyperventilations about it.
So what? For one thing, if melt rate happens to be higher one year than prior years, it might just be random changes in the snow line that are likely to reverse in later years. (Rather than evidence that things are much worse than we thought).
Maybe I give them more credit than they deserve, but I don’t see why there’s so much negativity about this paper that effectively says, it’s not as bad as they thought.
I think there is some confusion as to the mechanisms at work here.
“…provide an illustration of the difference in reflectivity between the two surfaces.”
Well, reflectivity is not the same as albedo. There is a fundamental difference in the way ice and snow absorb radiation. Like the ocean, ice is semi-transparent to it lets in wavelengths that do not leave easily. So ice can be said to be “more absorbent” or “captures a greater fraction” of the insolation. So far so good.
But when it comes to the albedo in the IR range, they are both basically black: emissivity water 0.978 and ice 0.966 (DOI 10.1080/01431169208904088 pp. 2879-2880)
Both cool effectively whether in or out of the sunlight.
Consider next, that the albedo in the visible and the albedo in the IR are different, and that the capture mechanism is also different.
This doesn’t mean the work is flawed, just that the mechanisms at work are not outlined well. I think it is important that they show the bare ground line is not really the point of focus, it is the snowline.
Albedo and reflectivity are often used interchangeably, and inaccurately! A smooth, flat surface of snow will have high albedo and high reflectivity. However, a rough snow surface (sastrugi), with a low sun angle at right angles to the ridges, will have considerable shadow areas. Thus, the albedo will be lower than for smooth snow. On the other hand, the sunlit snow, will have essentially the same reflectivity as the smooth snow. The sunlit fraction will thus absorb the same percentage of sunlight as smooth snow. However, the shadow areas (unlit fraction) will absorb NO direct sunlight! So, reduced albedo, if due to the surface being textured, does not mean increased absorption.
Actually, the situation is a more complex because the snow (and ice) have a bi-directional reflectance distribution function (BRDF) where the amount and direction of scattering is a function of the angle of incidence, which varies with both sun elevation and the angle of the reflecting surface. Also, the BRDF is different for ice (which has a significant specular reflection component) than for snow, and snow varies with compaction and impurities.
I think that the researchers need to learn more about diffuse reflectance before they make grand conclusions.
From the above press release: “In a finding that may help scientists better predict sea-level rise in a warming world, Brown University researchers have found . . .”
Well, one first needs to ask “Is there any need today for a better methodology for predicting sea-level rise?”
The answer to this question appears to be a straightforward “No.” Thirty years of data shows that the slope of a linear equation is an excellent model (and therefore predictor) of global sea-level rise in a warming world. Just refer to
“30 years of NOAA tide gauge data debunk 1988 Senate hearing climate alarmist claims”
https://wattsupwiththat.com/2019/03/05/30-years-of-noaa-tide-gauge-data-debunk-1988-senate-hearing-climate-alarmist-claims/
Of course, if Earth soon enters into a 20-100+ year period of global cooling, as is not-uncommon during interglacial period “short-term” transients, then we would certainly need a different prediction methodology and even the Brown University research would be of little help since, as J.C. Ryan admits, “We found that models don’t reproduce snowlines very well, which adds an uncertainty to future projections.”
Let’s not forget that while the southern edge of Greenland’s ice is melting, overall the ice volume is increasing, as is the overall volume of ice in Antarctica. So how will this study “help scientists better predict sea-level rise”?
So what is the driving factor delineating the snow-ice interface? Is it weather, such as the wind that blew the snow away and prevented the drones from flying, or is it climate? Is a fluctuation in the line a normal thing (weather) or is the line creeping back into the interior over time (climate)? Perhaps the causes of the snow -ice interface movement should be investigated.
So they’re reinventing the wheel. So what? They got money for air fare, lodging, hiking, camping, drones and any number of exciting and interesting activities culminating in academic publishing credits. You can’t get that money without tying your proposal somehow to “climate change”.
Yawn. Greenland ice melt — another boring & uninteresting scare-mongered issue. Is that all they got?
Nowhere in this article is the term “sublimation” used. Are Greenland’s ice and snow so different and if so, how?
Of course the snow and the ice also sublime (go directly from solid to gas phase). To the extent it happens, it all precipitates somewhere. Not all into the ocean I suppose. But the fraction that rains or snows into open ocean will be functionally equivalent to meltwater.
It’s true that solar energy absorption increases on bare ice relative to snow.
However, this can only lead to ice melt when the resulting surface temperature of the ice sheet exceeds 0 deg. C/32 deg F, unless there is substantial salt contamination of the ice surface, which then lowers the freezing point of ice. And whatever melting takes place is limited strictly to the ice/air barrier layer, not distributed throughout the entire ice pack column, all of which, given its extreme depth (measured in thousands of feet) remains at substantially below freezing on a perpetual basis.
More than half of Greenland never sees a temperature above freezing at the coastline/sea level, where influences from seawater temperature are substantial due to sea breezes and elevations are at or near sea level. Maximum daily temperatures (May through October) in the coastal areas range from 10 deg C/50 deg F in the extreme south to 0 deg C/32 deg F in the north coast.
Call it a maximum average daily high of 5 deg C/41 deg F across the entire coastal areas of Greenland.
Most of inland Greenland is at rather high elevation, however, with elevations as much as 10,500 feet. The normal temperature lapse rate is 3.6 deg F or 2.0 deg C. If the average interior surface elevation is the mean elevation of 5,000 ft msl (just my assumption for this analysis), then the standard atmospheric lapse rate suggests an average reduction in temperature with elevation over coastal areas of 10 deg C/18 deg F. Subtracting this temp reduction due to the standard atmospheric lapse rate from the average maximum daily max of just 5 deg C/41 deg F results in, on average, the entire island mass interior remains below 0 deg C/32 deg F even during the six warmest months of the year.
So, with this rather crude analysis, it seems that only an extremely limited surface area of Greenland’s southern coastline, at or very near sea level, can physically result in the melting of glacial ice, and only during the warm half of the year, and not inland where of course the vast majority of the surface area of Greenland exists.
Of course daily and hourly variations result in differences from these “averages”, but it is the average value that determines net ice melt in the jillions of tons of ice per year.
Just how then is Greenland contributing in any substantial way to rising sea levels?
Where is the computer model, based upon existing daily temperatures of monitored stations, and taking into account the effects of standard lapse rates and the very high ground throughout most of Greenland?
The only way that large scale melting of Greenland’s ice sheet can contribute substantially to sea level rise is if the icesheet boundary – and thus its total mass – is visibly retreating inland. Which does not appear to be the case.
Just went through a month of 5 to 10 below zero F temperatures (night) and very rarely above 20 F day time temperatures. Yet every day that the sun was shining I could see water vapor rising from the Ice that had filled the eves trough. The wisps of water vapor could clearly be seen, with the sun in the right position in relation to my line of sight. Over a week you could see the level of ice decrease bu 1/2 to 3/4 of an inch. And again this was with the temperature well below freezing between 10 and 20 degrees F. However, NO sun meant NO water vapor mist rising from the ice.
The same occurred to the ice on the driveway at the same temperatures. To prove to myself that it was the sun melting the ice, and caused by the sun warming the pavement I poured water on the drive and it was frozen solid in less than 5 minutes. Upon which it to started making wisps of water vapor.
You’re describing “sublimation” not melting. Sublimation is direct conversion to gaseous state (water vapor) from solid state, and it can occur at any temperature. Same thing happens with snow. Hence the term “freeze drying”. The rate of ice loss from sublimation is vastly less than from melting.
That’s not correct, Duane. In fact, the temperature cannot increase on the ice surface above 0C until the ice is gone. At the freezing/melting point there can be any proportion of liquid/solid from all solid to all liquid. Any heat added by insolation will go to latent heat until the phase change is complete.
In the summer there are rivers of meltwater. It’s my understanding that the sources can be far from the glacier edge. That’s normal seasonal effect and not a sign of global warming. The question is how much melts in summer vs accumulates in winter.
The surface of the ice must indeed reach the freezing temperature due to a temperature gradient in excess of freezing temp in the air above, at the very interface, in order for surface melting to occur. If the air temperature exceeds 0 deg. C it happens. If it does not exceed 0 deg C, it does not, provided the underlying icepack remains below 0 deg. C.
The temperature of the ice pack itself, as i stated, must at least reach freezing temperature in order to melt, and it does not unless there is an energy source below the surface of the ice pack that provides enough energy to bring a portion or all of the ice pack to freezing temperature … for instance, if there is geothermal activity in the underlying ground.
Then WHAT is causing the ICE to decrease/disappear from the eavestrough, creating a clearly visible steam like vapor, similar to the fog you see above an open pond ona sa sunny day when it is below ZERO? No drips, no drops, just a decrease in volume day after day – that the sun is shining.
sublimation of course. We are divided by a common language, eavestrough = gutter in ‘Murcan.
I’m pretty sure that’s not how much of the melting and sublimation is occurring, Duane. I don’t believe that conduction from the air is a primary cause. Certainly in some cases (not to my knowledge in Greenland though), there could be melting from below, caused by volcanic action below the ice. Most places though, it must be primarily radiative heating by the sun. That supplies latent heat for the phase change at the surface after raising the temperature of the ice in the surface layer to 0C from whatever temperature the bulk of the glacier is at. Nothing prevents there being a large temperature gradient from the 0C surface into the bulk of the ice, just as there is potentially a 20 degree or more gradient in the ocean from its surface through the thermocline to the deep ocean. Or use this thought experiment to prove it to yourself…Sea ice at the north pole may be at -40C at the air interface, but at some point it has an interface with the liquid ocean below. That surface must be at the freezing point of the salt water. That interface is in phase change with the ice either growing or melting away. So there is nothing preventing that 40 degree temperature gradient. (Do you imagine that the entire surface of the sea ice is held somehow at the freezing point of seawater and is therefore radiating heat away at around -2C?)
I think you would be correct to say that some of the meltwater in Antarctica (potentially like this video) is actually being caused by volcanic action, but you’d be wrong to say that the entire glacier has to be raised to 0C before any of it will melt or sublime.
https://youtu.be/dAOBbXQys78
There have been times in winter when I have seen a snowfall totally disappear over a period of a week or so, even though the air temperature remained well below freezing the whole time. It just takes direct sunshine to do the trick, and it seems to be almost all sublimation. Certainly in my back yard, we have no volcanic action that I’ve observed!
Duane
You said, “It’s true that solar energy absorption increases on bare ice relative to snow.” That is true for many by not all angles of incidence.
https://en.wikipedia.org/wiki/Fresnel_equations
Average lapse rate is about 0.7 C per 100 meters, and on average the melting zone on Greenland extends to about 1500 meters (5000 feet) altitude during the melt period (late May/early June to late August).
Very occasionally (like once per century) the melt zone extends to the entire area of the ice-cap. This last happened in 1888 and 2012. It was apparently more frequent during the previous interglacial.
Yes, there are always variability from the mean, both above and below the freezing point. But in order to provide data for a net melt of the Greenland ice cap there must be a net average air temperature at the actual surface elevation that exceeds the freezing point in order for melting to occur on a net basis. In most of Greenland most of the time (“on average”) that is not the case.
Of course, the way to determine the actual net melting of ice would require a large network of thermometers all over the Greenland ice sheet, and collect the data on a continuing basis to determine the net surface area exposed to melting air temperatures integrated over time.
But the climate alarmists don’t do that. They cherry pick certain spots that are known to melt, such as near the coastlines in the southern portion of Greenland, collect data and videos of the melted water running into crevasses, and pretend that that represents the entire Greenland ice sheet, and that this proves that the entire Greenland ice sheet is experiencing net ice loss, when their data and their videos do NOT prove that at all.
Additionally, the climate alarmists point to chunks of glacial ice that calve into the North Atlantic as proof that Greenland is losing its ice … while ignoring that the main driver for ice sheet movement towards the shore is the net ACCUMULATION of ice in the interior, such that gravity drives the ice (which though solid is still a fluid) downward to sea level, meaning of course outwards towards the shoreline. Water, as well as ice, always flows downhill.
Actually it is quite easy to see in satellite images which parts of the Icecap is actively melting at any particular time courtesy NASA:
https://worldview.earthdata.nasa.gov/?p=arctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Reference_Labels(hidden),Reference_Features(hidden),Coastlines&t=2018-08-05-T00%3A00%3A00Z&z=3&v=-1014813.989198516,-2580596.403010687,348130.010801484,-1975412.4030106869
The snow-free zone is much darker and has a network of supraglacial rivers and lakes. And these extend into the zone where the snow is actively melting. No expeditions needed.
Around here “snowline” refers to the elevation that snow turns to rain. It goes up and down with the weather and seasons. It sounds like these guys saw the snow blow away. Snowline is an inappropriate term.
As I understand it, Greenland coastal average temperatures only rise above freezing for about 3 months per year and only by warmer ocean influence. The much larger interior stays below freezing. That is not to say ice won’t melt there on a clear summer day. But the rest of the time when there is cloud cover or the sun is low or below the horizon, ice will not melt. This sounds like a 53% affect on part of a short season that could recommend a tweak on another phony bunch of models. Really, it sounds like a fun way for Brown grad students to fund an all expense paid vacation with free drones.
Well presumably you don’t live on a glacier. The author’s meaning of snowline was not ambiguous. It was clear that it was the line between bare ice and ice covered by snow.
“”””Each day, they flew their drones inland across the bare ice. When they reached the snowline, they recorded the position, turned their drones around and flew back. At one point during the field season, they had to stop flying for a few days because of high winds. When they got back to flying, they found something surprising.
“Suddenly the snowline was just gone,” Ryan said. “In a couple of days it had moved 30 kilometers or so up the ice sheet and was now out of the range of our drones. That was the first moment we thought we should investigate the effects of snowline movement on melt.”””””
From this I took it to mean the snowline was moved by wind. It does not mention the temperature of the wind or that the snow line moved because it melted.
I live between a pair of mountain ranges where the snowline is often clearly visible and different from drifting snow. I’m not trying to pick on the term. I just don’t see how glacial melt rate models are refined by “snowlines” that are moved by winds. More likely it would add chaos to the calculation.
If the author meant that the snowline moved 30 km because the freezing level rose and the snow melted, then the term is good and my reading was in error. But I don’t so.
Co-opting an established term with a new meaning is confusing. Call it a Blowline.
Actually the lower parts of the icecap is regularly above freezing during June, July and most of August.
Claude summed it up perfectly, its all about Grant Money.
So what if there is a bit of melting, it would be more than made up by snow.
As too the models, they will be adjusted to match what the modellers want to see.
As to the world cooling ?, if this should happen, the Warmers lobby will claim the credit for it saying that all their recommendations are finally working, and will demand that we continue to de-carbonise.
I know that I keep saying it, but only when the likes of President TRUMP finally shows that CO2 is a good gas, and that as its the only reason for the whole warming myth, it should be the end of this nonsense.
Everything else is just a excuse for the so called Climate Scientists having fun at the taxpayer expense. , plus the top people of the Green movement still trying to force us to accept Communism mark two.
MJE