Guest Post by Willis Eschenbach
There’s a new study in PNAS, entitled “Observational determination of albedo decrease caused by vanishing Arctic sea ice” by Pistone et al. Let me start by registering a huge protest against the title. The sea ice is varying, it isn’t “vanishing”, that’s just alarmist rhetoric that has no place in science.
In any case, here’s their figure 4B, showing the decrease in albedo from the “vanishing” sea ice:
Figure 1. Graph from Pistone2014 showing CERES albedo data (green, solid line) for the ocean areas of the Arctic.
The authors say:
Using the relationship between SSM/I and CERES measurements to extend the albedo record back in time, we find that during 1979–2011 the Arctic darkened sufficiently to cause an increase in solar energy input into the Arctic Ocean region of 6.4 ± 0.9 W/m2, equivalent to an increase of 0.21 ± 0.03 W/m2 averaged over the globe. This implies that the albedo forcing due solely to changes in Arctic sea ice has been 25% as large globally as the direct radiative forcing from increased carbon dioxide concentrations, which is estimated to be 0.8 W/m2 between 1979 and 2011.
The present study shows that the planetary darkening effect of the vanishing sea ice represents a substantial climate forcing that is not offset by cloud albedo feedbacks and other processes. Together, these findings provide direct observational validation of the hypothesis of a positive feedback between sea ice cover, planetary albedo, and global warming.
So … how are they going about making that case?
Let me start by saying that looking at albedo as they are doing is a very roundabout and inaccurate way of handling the data. The CERES dataset doesn’t have an “albedo” dataset. Instead, they have a dataset for downwelling solar, and another dataset for upwelling solar. The problem is that when the numbers get very small, the values of the calculated albedos get more and more inaccurate. Albedo is reflected solar divided by downwelling solar. So when you get down to where there’s almost no sunshine, you can get things like a gridcell that averages 0.2 W/m2 of incoming sunlight over some month, and reflects 0.4 W/m2 … giving us an impossible albedo of 2.0 …
It’s not clear how Pistone et al. have handled this issue. The way I work around the problem is to calculate the average upwelling reflected sunlight for the Arctic ocean area, and divide that by the average downwelling sunlight for the Arctic ocean area. This gives me an overall average albedo. I get slightly different numbers from theirs, and I am unable to replicate their results. However, I do get about the same trend that they get over the period, a decrease in the albedo of about 1.5% per decade. However, I don’t particularly trust those albedo numbers, averages of ratios make me nervous.
For this reason, I use a different and simpler measure, one which Pistone et al. mention and quantify as well. This is the actual amount of sunlight that makes it into the climate system. The authors call this the “total solar energy input”, and I will follow the practice. And qualitatively, my results agree with theirs—the amount of sunlight absorbed by the arctic has indeed increased over the period of the CERES data, 2000-2013. Figure 2 shows both the clear-sky and the all-sky arctic total energy input:
Figure 2. Increase in solar energy input to the Arctic ocean areas, 2000-2012. Clear sky in black, all sky in red. Units are area-weighted watts/m2.
In addition to the overall trend in all sky solar input (green line), you can see the peak in energy input in 2007, with the high solar input corresponding to very low ice areas. Overall, Figure 2 shows an even greater increase in energy input than Pistone2014 have estimated over the entire period. They report an increase in Arctic solar energy input over the ocean of 0.21 W/m2 over 32 years … and the CERES data shows an increase of 0.3 W/m2 per decade.
So we’ve established that their first claim, of increasing solar energy input to the Arctic ocean area 2000-2012, is true, and perhaps even underestimated. And this is quite reasonable, since we know the sea ice has decreased over the period … but what about their second claim? As you may recall, this was (emphasis mine):
The present study shows that the planetary darkening effect of the vanishing sea ice represents a substantial climate forcing that is not offset by cloud albedo feedbacks and other processes. Together, these findings provide direct observational validation of the hypothesis of a positive feedback between sea ice cover, planetary albedo, and global warming.
The CERES data agrees that the increase in solar energy input from reduced ice cover is not counteracted by Arctic clouds … nor would I have expected it to be counteracted by clouds in the Arctic. As I have discussed, well, more than once, the main climate control system is in the tropics. So if this increase in absorbed energy were counteracted by clouds, my hypothesis is that it would happen be in the tropics. I’ll return to this in a moment.
First, however, they’ve claimed that their results establish the existence of “a positive feedback between sea ice cover [and] planetary albedo”. Since the planetary albedo controls the total solar energy input to the globe, let’s take a look at the same data as Figure 2, total solar energy input, but this time for the entire planet …
Figure 3. Available solar energy at the top of atmosphere (red) and total solar energy input to the globe (blue), 2000-2012. Units are area-weighted watts/m2.
So their claim of increased solar energy input to the Arctic from reduced sea ice is true … but their claim that there is “a positive feedback between sea ice cover [and] planetary albedo” is falsified by the CERES data. The total solar energy input (blue line above), and thus the planetary albedo, is amazingly stable over the time period. There is no feedback at all from the changes in the ice.
To illustrate the stability, Figure 4 shows a breakdown of the total solar input data (blue line above). It’s divided into panels that from top to bottom show the data itself, the seasonal pattern, the trend, and the residuals of the global solar energy input:
Figure 4. Decomposition of the solar energy input signal into trend, seasonal, and residual components. Red scale bars on the right indicate the relative scale of the individual panel. Units are area-adjusted W/m2.
I’ve written before about the amazing stability of the climate system. This is another example. In the past people have objected that the system is forced to be stable, because over time, energy out must generally equal energy in.
But the global solar energy input, the amount of the available solar energy that actually makes it into the climate system, is under no such constraint. There is nothing that it must balance to. Solar energy input is a function of the albedo, which is determined by clouds, snow, ice, vegetation, and wind, and all of these are constantly varying in all parts of the planet … and despite that, the swings of the trend are no greater than ±0.3 w/m2 over the period. The maximum monthly deviation from the seasonal average is a mere one W/m2, and the standard deviation of the residuals (data minus seasonal) is half a watt/m2.
So … how does it happen that we have a strong increase in solar energy input in the Arctic, but the global energy input stays the same?
Well … as I mentioned above, the tropics. Over the period 2000-2012, during which the Arctic received increased solar energy input, here’s what’s happened in the tropics:
Figure 5. Total solar energy input, all skies, tropics. Units are area-adjusted W/m2
As I hypothesized, the control is happening in the tropics. Pistone et al. note that the Arctic solar input is going up because of decreased sea ice … but they did not notice that at the same time, the tropical solar input is going down because of increased clouds. And the net sum of all of the changes, of more energy being absorbed in the extra-tropical areas and less energy being absorbed in the tropics, is … well … no change at all for the globe. It all averages out perfectly, with little change in either the monthly, annual or decadal data.
Coincidence? Hardly.
This is about as neat a demonstration as I can imagine in support of my hypothesis that the system is not ruled by the level of the forcings—instead, it is regulated by a system of interlocking emergent climate phenomena. A number of these phenomena operate in the tropics, and they have a curious property—the warmer the planet gets, the more that they cut down on the incoming solar energy.
So at the end of the day, we find that the claim of the authors that increased solar input to the Arctic is connected to the planetary albedo to be true … except that it is true in exactly the opposite of the direction that they claimed. When more energy is absorbed in the Arctic, less energy is absorbed elsewhere.
In closing, I want to highlight what it was that got me interested in climate science to begin with. I wasn’t interested in finding out why the global temperature had changed by something like ± 0.3°C over the 20th century.
Instead, I was interested in finding out why the global temperature had only changed by ± 0.3°C over the 20th century. I was amazed by the stability of the system, not the fact that it had varied slightly. So let me close with a graph showing the total global solar input residuals, what remains after the seasonal cycle in total solar input is removed.
Figure 5. Residual total solar input after the seasonal cycle is removed. Dotted lines show the inter-quartile range. Smooth curve is the loess trend line.
The monthly deviation from the seasonal cycle is tiny. Half the months are within a third of a W/m2 of the seasonal average … a third of a watt, to me that’s simply amazing.
Now, you might disagree with my hypothesis that the planet is thermoregulated by emergent climate phenomena such as thunderstorms, El Nino, and the PDO.
But the stability shown in the above graphs surely argues strongly for the existence of some kind of regulatory system …
My regards, as usual to everyone.
w.
AVISO: If you disagree with what I or anyone says, please quote the exact words you disagree with. It allows everyone to understand exactly what you are objecting to.
DATA AND CODE: You’ll need the CERES data (227 Mb) , the CERES surface data (117 Mb) and two support files (CERES Setup.R and CERES Functions.R) in your R workspace. The code is Arctic Albedo.R, it should be turnkey.
[UPDATE]
Well, y’all will find this funny, I assume … following up on the question of the net effect of the loss of the sea ice that came up below in the comments, I decided to see what was happening with the upwelling longwave. We’ve established that the loss of the ice increases the total solar energy input … but what about the energy loss via longwave? (Yr. humble author slaps forehead for not thinking of this sooner …)
As you can see, the change in solar energy input is more than offset by increased losses … so the net effect of the melting sea ice is a net energy loss of 0.05 W/m2 per decade.
Note again the stability over time. Note also that this part of the system is not constrained by any need for solar input and longwave output to be stable, or to have the configuration they have. The average solar input is 30 W/m2, and the average longwave loss to space is 63 W/m2 … and despite the marked changes in ice cover over the period, they’ve only changed about 1% per decade over the period …
Gotta love the climate, always more surprises …
w.
[UPDATE II]
Some folks have said that there is a problem with my area-weighting, so let me explain exactly what I did.
The data exists in 180 latitude bands. The center of the bands start at -89/5° (south) and end up at 89.5° (north). To area-weight the data, we want to adjust the results for each gridcell by the area.
What we want to do is adjust the results to give what you would get if they had the size of the average gridcell. Now the area is proportional to the cosine of the mid-latitude. So what we do is multiply each gridcell result by
area of the gridcell / area of the average gridcell
This give each gridcell the value it would have if it were of average size. The effect of tiny gridcells is reduced, and the effect of large gridcells is increased.
Now, what is the average cell size? Well, if we integrate Cos(x) from zero to pi/2, we get 1. So the average gridcell size is 1/(pi/2) = 2/pi ≈ 0.637.
As a result, the weighting factor by which we multiply the gridcell value is, as you recall:
area of the gridcell / area of the average gridcell
which is equal to
cosine of the gridcell midlatitude / 0.637
Once you’ve multiplied the data by those weighting factors, you can compare them directly, as they are all adjusted to the average gridcell size.
The way to test if you’ve done this correctly is to see if the plain vanilla average of the newly-weighted dataset is correct. For example, see the average available solar (~340 W/m2) and solar input (~240 W/m2) values in Figure 3. They are simple averages of weighted data.
Note that there are two ways to do the weighting.
The first is to do all calculations (trends, etc) using the unadjusted variables. Then to get an average, you use what is called an “weighted mean”, which weights the data on the basis of gridcell area as it calculates the average.
The other way to do it is the way I described above, which converts all of the data to what an average sized gridcell would show. Once you’ve done that, you no longer need to do an area-weighted average, because the data itself is weighted. This means that you can use a normal average, and compare things like trends directly.
So … what I do to check my work is to compare the normal mean of the area-weighted data, with the weighted mean of the original data. They should be the same, and that is the case in this analysis.
Finally, an area-weighted mean uses different weights, where the sum of all of the weights is 1. This allows you to calculate the weighted mean as the sum of the product of the data and the weights. These weights are different than the weights I used to area-weight the data itself. These weights which do not sum to 1. However, the end result is the same.
GregK says:
February 18, 2014 at 4:34 am
… Occasionally things get out of whack, for instance the snowball [or slush ball] earth around 650Ma, but generally things stay within bounds that favour the survival of critters.
>>>>>>>>>>>>>
Actually you have it backwards the interglacials like the Holocene are brief warming during a snow ball earth default conditions.
Take a close look at the graph I posted of the last four interglacials. Overall the earth has been cooling GRAPH: 65 million years expanded graph for last five million years.
That is why geologists generally laugh at Climastrologists.
Angech says: @ur momisugly February 18, 2014 at 5:06 am
… This heat differential in the Northern to the Southern Hemisphere is rarely talked about and most effects are instead put down to having more land surface in the northern hemisphere when it is really a combination of both….
>>>>>>>>>>>>>>>>>
John Kehr, touch on it in his article – Misunderstanding of the Global Temperature Anomaly.
If the dominant energy supply were solar rather than coal, the religious environmentalists would probably be adopting the theory that man is taking solar energy away from the ecosystem.
MikeN says:
February 18, 2014 at 7:23 am
————————————————
That is too true to be funny.
@David in Cal says:
February 18, 2014 at 2:16 am
“The science here is beyond me. However, what about Antarctic sea ice? I believe that Antarctic sea ice extent has expanded by almost the same amount as Arctic sea ice has shrunk. So, would the planetary impacts of northern and southern albedo changes cancel out?”
I think the Antarctic gain of ice mass may offset the Arctic loss of ice mass. However:
(1) Antarctic gain detracts water from the sea and causes a decrease ub sea level, whereas Arctic loss of (floating) ice does not affect sea level;
(2) net ice accumulation in Antarctica is mostly over land that was already covered by ice, so that it does not have much effect on albedo, whereas ice melting in the Arctic causes the area to turn from white to dark, reducing albedo.
(3) there apparently is some loss of floating ice in West Antarctica, which would also reduce albedo just as a melting Arctic ice would do. However, the Antarctic melting may not be significant in relation to the process occurring in the North.
Once Antarctic sea ice is taken into account there has been essentially no change in GLOBAL sea ice since 2000 (or 1979), yielding no net polar albedo effect. So why would the tropics show a downward trend in total absorbed solar? That would be Willis’ thermostat increasing clouds and albedo in response to the higher level of GHGs. That is the small change in interpretation that I would put on Willis’ CERES findings.
On the original paper’s estimate of the size of the local albedo feedback mechanism, it is important to note that this local feedback effect is asymmetric in the warming and cooling directions. As the planet has warmed the marginal feedback effect from further warming and further polar ice melting has gotten smaller and smaller, as the sea ice has retreated to higher and higher latitudes where surface areas and solar incidence both get smaller and smaller.
In the cooling direction these marginal effects get larger and larger as snow and ice descend to latitudes that cover vastly more surface area and where the sunlight is coming in at progressively steeper angles where it would do much more warming if it weren’t being reflected away. At some point we know that this cooling-direction albedo feedback overwhelms whatever thermostatic processes are at work in the climate system, causing the planet to descend at regular intervals in 100,000 yr long glacial periods.
This asymmetry is a main reason why we need to be more concerned about cooling than about warming: it really can reach a tipping point and we damn well better be prepared to counter it. My suggestion, which I have reiterated a few times here, is to dot the great white north with soot generation plants that can spew all winter, but we had better get them built before glacial expansion gets rolling. If we wait until we know we’ve got a problem it could well be too late. Once snow and ice build-up begin in earnest, the great white north is not going to be a hospitable place for major infrastructure projects.
We don’t have the technology yet to deflect mass-extinction causing asteroids and just have to hope that the next of these 100 million year events is not timed for the next century, but we do have a simple low-tech answer to the not quite so devastating but much-more-likely-to-hit-us-anytime-now next glaciation. We really need to get on it.
Willis,
You state: “Solar energy input is a function of the albedo, which is determined by ….. wind.”
Not sure I follow this.
Please can you explain or provide a link relating to this, to explain how this effect works?
milodonharlani says:@ur momisugly February 18, 2014 at 4:26 am
William Astley says: @ur momisugly February 18, 2014 at 6:00 am…
>>>>>>>>>>>>>>>>>>>>>>>>>
About the decrease in Arctics [sea] ice and greater sea ice extent in the Antarctic, everyone is ignoring the fall 2012 paper Can we predict the duration of an interglacial?
WUWT discusion
From the paper:
This is not a paper to give one the warm fuzzies. This is the reason I have been looking at papers on Drake Passage especially after retired EPA scientist F. H. Haynie said:
A tongue of cold water from the Antarctic Circumpolar Current just before Drake Passage, heads up the coast of South America to Galapagos as the Humbolt Current “i a cold, low-salinity ocean current that flows north along the west coast of South America from the southern tip of Chile to northern Peru.” (WIKI)
The Antarctic Circumpolar Current is wind driven and who knows what effect increasing ice will have on the Humbolt Current.
Willis and Bob Tisdale have done a lot of research on what is going on in the tropics but very little work has been done on what is happening in the Antarctic and how it effects ENSO.
““No sensible person disputes the greenhouse effect (i.e. the GHE).”
We color me an non nonsensical idiot.
So back to an ongoing question that nags me that no one has been able to answer..
Given a concentration of CO2 and radiation field (watts/m^2) what is the rate that CO2 converts one form of radiation to another?
This should be a simple answer, right? I see a lot of articles that describe how GHGs supposedly work. Alas, no one has be able to show me how they work mathematically. Kinda important I think.
We can talk about how strong an electromagnetic field is all day till we turn blue watching the cows come home. Until we theoretically quantify it i.e. x amount of incoming radiation + Black box (CO2) = .15x amount of outgoing radiation or what ever the amount is since it can not be 100% efficient, then we are just blowing smoke up our own well you know where I am going with that.
Much like I know given a fuel, a burn rate and turbine size, I can predict the output of the Brayton Cycle. I should be able to establish a set of equations that does the same for CO2!
CO2 convert one wavelength of electromagnetic radiation to another wavelength (that photon thingie) else it would be transparent to that wavelength.
input (processes) = output.
For direct observations in the Arctic see the following link.
“PSD’s Polar Observations and Processes team and Environment Canada erected a 10.5 m flux tower in Eureka, Nunavat, Canada in 2007. At the top, we installed upwelling/downwelling shortwave and longwave radiation instruments . Downwelling instruments are facing up, measuring solar radiation from the Sun, while upwelling instruments are looking down, measuring radiation from the ground. Kipp and Zonen CM22 radiometers measure shortwave radiation, while Eppley PIR radiometers measure infrared radiation.”
http://www.esrl.noaa.gov/psd/arctic/observatories/eureka/eureka_tower.html
I would argue that for the last 2.6Ma the climate has been demonstrably bistable and not very tightly regulated in between.
It’s important to realize that a feedback represents the derivative of the flux with respect to temperature, not time. The absence of a trend in global shortwave may only reflect an absence of a trend in temperature, leaving the feedback ambiguous.
My own examinations of daily CERES data and daily LT temps indicated a strong global negative feedback from the shortwave.
Sort of, but not quite fully correct.
Albedo of Arctic sea ice changes only based on day-of-year. Albedo starts high at 0.82, stays steady at 0.82 until May, decreases through the summer to a low of 0.46, then rises again to 0.82 until about September, then remains at 0.82 until the end of December. This is from Dr Curry’s measured data.
1. Albedo of sea ice does NOT change with latitude.
2. Albedo of open ocean changes with every HOUR of every day as the solar elevation angle changes each minute. Specifically, open ocean albedo does NOT change explicitly with latitude, but latitude affects the overall SEA change over day-of-year AND latitude and hour-of-day (HRA), These changes are based on the earth’s declination and geometry and is strictly and specifically defined. But, Hour-of-day and day-of-year CANNOT be separated from latitude.
3. Opposite the above, the yearly maximum solar radiation occurs in early January at 1410 watts.m^2. The minimum solar top-of-atmosphere radiation occurs July 3, when the Arctic sea ice is decreasing strongly day-by-day, BUT while Arctic sea ice is between min and max. Roughly, the edge of Arctic sea ice is between 74 and 76 north.
At the point of maximum solar radiation at TOA, the ANTARCTIC sea ice is is a wide “ring” slowly varying from 59.2 south (last October under 1370 watts/m^2) to about 64 south latitude (in January under 1410 watts/m^2) to a minimum sea ice extent at 3 Mkm^2 (in March at 70 south latitude back down to 1360 watts/m^2). So, when the TOA solar radiation is at its maximum, ARCTIC sea ice is dark. When the top-of-atmosphere radiation is at its max, Antarctic sea ice is not at its minimum.
Net effect: As a whole, Antarctic sea ice is MUCH, MUCH closer to the equator every day of the year.
Overall, increased heat losses from open ocean in the Arctic (when Arctic sea ice is at a minimum in late August-September) are much greater than increased heat absorbed into that open water. More sea ice loss in the Arctic => More heat loss from the planet and a net cooler planet.
The opposite happens in the Antarctic: More sea ice around Antarctica means more heat reflected from the planet and a net cooler planet.
It is not really necessary to “combine” or group the other two parts of the Antarctic
Up north, the Arctic Ocean STARTS at 70 north latitude, and this IS the southern limit of the Arctic Ocean. Essentially ALL “Arctic sea ice” then cycles between 70 north latitude (at MAXIMUM extents at 14.0 Mkm^2) and 80 north (if 4.0 Mkm^2). In the future, this minimum could go even closer to the pole: if there were 1.0 Mkm^2, all the arctic sea ice is a little beanie cap from the pole to 85 north latitude.
Cherry picking observations in REGIONS and IMPLICITLY extending to the GLOBAL.
15 yards, and no change in “down”.
Ocean Albedo behaves differently for direct radiation and diffuse radation.
Diffuse radiation: Does not vary with wind speed, water turbidity, algae or plant levels, or solar elevations angles. Usually, open ocean albedo is = 0.065
Direct radiation: Varies strongly (from 0.035 to 0.45) with solar elevation angles.
At any given solar elevation angle, ocean albedo will decrease (more energy can be absorbed) as wind speed increases from 0. Usually, higher wind correspond to increased cloud cover also.
Gail Combs says:
February 18, 2014 at 8:01 am
Truly cause for concern if the Holocene’s days are numbered, instead of being a super-interglacial (in duration, not intensity).
Leif thinks that Bond Cycles are fictitious if not fantastic, but long ago on WUWT, I expressed the fear that our interglacial might have only one & a half such cycles (if such they be) left before another Big Ice Age, ie the rest of our current warm cycle, plus the next Less Little Ice Age Cold Period, followed not by recovery but renewed descent into the frigid depths. The long-term T trend since the Minoan (so-called) Warm Period, if not indeed the Holocene Optimum, has been down.
So the 1970s alarmists were closer to being right than the present CACA crowd.
False.
The Antarctic sea ice is INCREASING at all times of the year.
The Antarctic sea ice cycles between a minimum of of 4.0 Mkm^2 at latitude 70 south, to a maximum of of 19.5 Mkm^2 at latitude 59.2 south.
The Arctic sea ice only varies between 72 north and 82 north.
On EVERY day of the year, Antarctic sea is exposed to 2 to 5 times the radiation that Arctic sea ice receives, and is therefore Antarctic sea ice is 2 to 5 times MORE important to the earth’s heat balance than the Arctic sea ice. (But the tropics are even more important.)
Max Hugoson says:
February 18, 2014 at 8:48 am
The penalty for making up “data” should be forfeiture of the game.
Temperature “records” from the 20th & 21st century must now forever carry asterisks, as do the corrupt home run records of McGwire and Sammy Sosa.
A required cross check would be to look at a validated dataset for global albedo from 1981 to present. GLASS is one of two that exist. The PI for GLASS is pretty good about answering questions if you write to him. It’s validated against FLUXNET ground stations and has both white sky and black sky albedo.
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6351353&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6351353
Why worry about how much sunlight is entering the system, when the backradiation is twice as intense?
Great post, Willis. Some great comments too!
Replying to each of the above:
(1) False. Arctic sea ice floats on the Arctic Ocean. 19.5 Mkm^2 of Antarctic SEA ice also floats AROUND the 14.0 Mkm^2 Antarctic continent AND around the 3.5 Mkm^2 antarctic fixed ice shelves. You are somehow getting the 17.5 Mkm^2 permanent Antarctic continental ice mixed up with the 19.5 Mkm^2 varying Antarctic sea ice. At Antarctic sea maximum, there is a total of 14.0 land ice + 3.5 permanent fixed ice shelves + 19.5 sea ice = 37.0 Mkm^2 of total ice.
(2) False. Dead wrong. The steadily increasing Antarctic sea ice is 2x to 5X MORE important in reflecting solar radiation than what little bit of Arctic sea ice is present at very high latitudes.
(3) False. Totally misleading. That “some remaining” antarctic sea ice at minimum sea ice extents is LARGER than all of Greenland’s ice. (Not more massive, but larger in area). The EXCESS Antarctic sea ice in October last year at latitude 60 south was LARGER than the entire Hudson Bay occupied at 60 north!
Amatør1 says:
February 18, 2014 at 9:05 am
Why worry about how much sunlight is entering the system, when the backradiation is twice as intense?
*******
Bingo!
And how much actually does “work” on the climate?
Nice work Willis.
The one thing that seems missing from both the paper and you re-examination is the change in out-going LW.
How can they possibly discuss “feedback” without assessing the full spectral impact of any changes? They show a +ve feedback in solar input but open water is nearly “black” in terms of LWIR. So if there’s more open water this also means more heat lost to space and that happens when the sun is out as well as well into the long polar night
The other missing factor is direct surface reflection from open water and melt pools. This will mostly get missed by instruments aimed at the surface which are too sensitive to take full face shot of solar and have to shut a protective flap.
When sun is at glazing incidence and a satellite is in a position to measure it , it’s probably in safety mode and not watching.