Arguments
Greenland's ice mass loss has spread to the northwest
Posted on 30 March 2010 by John Cook
Past studies have found most of Greenland's ice mass loss had occured in the south. However, new research has been published (Khan 2010) examining the pattern of mass loss over the entire Greenland ice sheet (H/T to Riccardo). Satellite gravity data and Global Positioning System (GPS) measurements both find that mass loss has been spreading up along the northwest coast of Greenland, starting in late 2005. This increase in mass loss is shown most dramatically in this animation created by co-author John Wahr:
Ice mass loss from Greenland
GPS data is obtained by placing GPS receivers on bedrock adjacent to the ice sheet. As the massive Greenland ice sheet loses mass, the bedrock undergoes vertical crustal uplift. Bedrock near the Thule Air Base on Greenland's northwest coast rose by about 4 centimeters from October 2005 to August 2009. As accelerating ice mass loss causes accelerated crustal uplift, the observed uplift show strong agreement with the loss of ice mass measured by satellite gravity data. These observations indicate that the accelerated mass loss is dominated by the increasing velocity of outlet glaciers. Large glaciers in the north-west region are sliding downhill faster and dumping more ice in the ocean.
The GPS data provides yet another line of evidence that the Greenland ice sheet has been losing mass at a significant rate. Satellite radar altimetry and airborne laser altimetry have observed thinning near ice sheet margins. Radar interferometric surveys find that glaciers are sliding faster in the ocean. And the overall picture given by the satellite gravity data shows that mass loss of the entire ice sheet is still accelerating (Velicogna 2009).
What will happen to Greenland in the future? Various independent studies predict global sea level rise of around 1 to 2 metres by 2100, with Greenland being a significant contributor (Vermeer 2009, Pfeffer 2008). Models predict that at the rate we're emitting CO2, collapse of the Greenland ice sheet is likely within the next few centuries (). This is backed up by studies of earth's past history which find ice sheets are highly sensitive to warmer temperatures. Global temperatures just 1 to 2°C warmer than now saw sea levels over 6 metres higher than current levels (Kopp 2009).
Science is about piecing together the full body of evidence to improve our understanding. As more data comes in, we're now seeing many lines of evidence painting the same picture. The Greenland ice sheet is highly sensitive to warming temperatures and is likely to contribute sea level rise in the order of metres.
UPDATE 2 Apr 2010: Many thanks to Robert Simmon at NASA who pointed me in the direction of another instructive animation of ice mass loss from Greenland as measured by the GRACE gravity satellites:
Last paragraph typo: pointing painting (delete pointing)
We'll have to wait till 2013 to find out.
Thanks for the typo alert.
You read it here first ;)
And here's another connection from a recent study of caves in the southwestern US.
"Both research teams found that climate in the Southwest oscillated rapidly between wet and dry as the North Atlantic cooled and warmed between 50,000 and 10,000 years ago. Their findings reinforce computer model predictions of similarly abrupt climate change during the coming century, as emissions of greenhouse gases, such as carbon dioxide, heat the atmosphere."
Other questions, what would constitute a collapse of one of the ice sheets? And do you think there is a failing mechanism for an ice sheet that would lead to collapse? If so, what kind of thing are we looking for.
Because of my job in coastal engineering, I'm very interested in sea level rise. Even a one meter rise would lead to a mind boggling amount of problems to current coastal structures. Let alone if we are confronted with a 2 or more meter rise.
I'm wary of statistical extrapolations of the current accelerating trend of ice mass loss. The reason is there are physical constraints on how fast the glaciers can move so one imagines (hopes) eventually the rate of ice mass loss might stabilise. Note - that's the rate of ice mass loss that might level out - I'm not saying mass balance will stabilise. Therefore papers like Pfeffer 2008 are useful in that they look at the physical constraints of Greenland's glaciers, leading to an estimated sea level rise of 1 to 2 metres by 2100.
I will not discredit any paper, simply because I do have not the necessary background to do so in any constructive sense. I do however doubt the overall accuracy of the predicted sea level rise, because in so far I was able to follow it, it has mostly been on the conservative side. Since the current ice loss in in both the Arctic and Antarctic is going faster than almost all of the projections, that would lead to the conclusion that maybe our long term prediction might be off as well.
An other factor is, in so far as I have read and am aware of, is that our current understanding of ice sheet dynamics and glacier flows is not that well know as we would like and problematic in some aspects. Coupling that to the astonishing rate that the glaciers are retreating and that some mayor glaciers might not be so protected or constrained as we thought they were, to me gives enough reason to do a re-evaluation of current projections or at least do a major worst case scenario exercise.
Here are the conclusions from Velicogna (2009):
"We showed that a detailed analysis of the GRACE time series over the time period 2002–2009 unambiguously reveals an increase in mass loss from both ice sheets. The combined contribution of Greenland and Antarctica to global sea level rise is accelerating at a rate of 56 ± 17 Gt/yr2 during April 2002–February 2009, which corresponds to an equivalent acceleration in sea level rise of 0.17 ± 0.05 mm/yr2 during this time. This large acceleration explains a large share of the different GRACE estimates of ice sheet mass loss published in recent years. It also illustrates that the two ice sheets play an important role in the total contribution to sea level at present, and that contribution is continuously and rapidly growing."
Readers might be interested to know that over the last 3 summers, an extensive GPS network has been established all over Greenland, the new GNET GPS network. Quite a few new sites have been built in Antarctica as well. Over the next few years, the change in ice mass will be weighed very effectively by GPS.
However, I do wonder if this (acceleration) will be a continuing trend, or that it has been caused by weather or one of the many oscillations (which I hope, but wouldn't count on it). The measurement time series are still rather short. I find it somewhat surprising that these great ice masses have such a rapid response on climate, because usually such large bodies of ice have considerable inertia (e.g. the Antarctic ice sheet is still responding to the current Holocene (?)). I'm not sure though, and I should maybe talk about this with some of the experts at our research institute (IMAU).
"Response: [...] "an estimated sea level rise of 1 to 2 metres by 2100"
Get real. Current mass of Greenland ice sheet is somewhere around 2.4 × 1018 kg. Average loss between April 2002 and February 2009 is estimated to be 2 × 1014 kg/year. That is 0.0083%.
On the other hand, global ocean surface area is some 3.6 × 1014 m2. A one meter increase by Greenland ice melt would require 3.6 × 1017 kg, which is 15% of the entire ice sheet mass.
If that much ice is supposed to melt in nine decades and acceleration of melting is uniform, in the final year (2100) the annual melt should be 1.2 × 1016 kg, sixty times more than the 2002-2009 average.
The bulk temperature of Greenland ice sheet is around -30 °C. To warm it up to 0 °C and melt requires about 4 × 105 J kg-1. So to melt that much ice in a single year takes 4.8 × 1021 J, that is 1.5 × 1014 W. As the surface area of the ice sheet is 2 × 1012 m2, the average heat flux required is 75 W m-2. That's much. The average annual insolation at TOA (Top of Atmosphere) over Greenland is 193 W m-2, most of it reflected back to space by clouds and the ice surface itself. And even at -30 °C, outgoing heat radiation of ice surface is 198 W m-2 (it is 315 W m-2 at 0 °C).
The source for sea level rise of 1 to 2 metres by 2100 are two peer-reviewed papers, Vermeer 2009 and Pfeffer 2008. These papers use two independent methods to come to the same answer. Pfeffer in particular looks at the physics of glacier discharge and finds accelerating discharge of glaciers into the ocean the main reason why sea level rise is so large.
Accelerating glacier discharge has already been observed by radar interferometric surveys. This is corroborated by GPS observations in Khan 2010.
unfortunately no one still came out with a reliable ice sheet dynamics model. The IPCC AR4 did not include the ice sheet melting contribution to sea level rise because a reliable prediction was not possible.
From then, scientists made a few step forward, but more than this it is the new data that rise concern. Although still not conclusive for accurate projections, the new data show acceleration of melting in Greenland, in West Antarctica and possibly even in East Antarctica. And we know from paleo reconstructions that rates of the order of meters per century are indeed possible.
Although no one can say conclusively that the current acceleration trend will continue, all the signs point in this direction.
As for The Netherlands, already in 2008 your Delta Commitee projected 0.65-1.3 meters by 2100. They included the caveat of the unknown response of Greenland and Antarctica ice sheets and concludes "that this level may be higher than has been assumed up till now.". But, according to the Delta Committee, the impact will vary in different part of the coast. The engineer point of view is not general and needs an expert and specific advice.
Thank you for giving us the correct numbers, and a more realistic view on the Greenland ice, than the ones coming from makers of the usual panic reports!
In Wikipedia (''Greenland ice sheet'') I just read that 'the warmest decades were the 1930s and 1940s'. Not now. Why was nobody alarmed 70 years ago?
Also, (Wikipedia) mean annual temperatures on the ice sheet domes are -31°C (on the north-central part of the north dome), and -20°C (at the crest of the south dome). How is ice going to melt with those kind of temperatures?
John Cook wrote Various independent studies predict global sea level rise of around 1 to 2 metres by 2100, with Greenland being a significant contributor (Vermeer 2009, Pfeffer 2008).
That does not mean that Greenland's contribution alone would be 1-2 m of SLR.
Read the two papers that John linked. Pfeffer et al. 2008 derive total SLR of 0.8 to 2.0 m by 2100, with 0.2 to 0.5 m of that coming from Greenland and the remainder from Antarctica, other glaciers & ice caps, and thermal expansion. Vermeer and Rahmstorf 2009 give a range of 0.8 to 1.8 m by 2100, again including a mix of contributions from all the above sources.
From the Velicogna paper that BP cites, ice mass lost from Greenland in 2007-2009 averaged 286 Gt/yr. The 21st century average would only have to be a factor of about 4-5 greater than this to yield +0.3 m SLR from Greenland and +1 m SLR total. Considering that the rate of loss of mass from Greenland doubled over the 2002-2009 period, this doesn't seem especially farfetched.
Ice melts below the equilibrium line, and ice is discharged into the sea by marine terminating glaciers. Ice in the center of the sheet then flows outward.
If that acceleration dropped to 3% per year tomorrow and continued for the rest of the century, you'd end up with 0.3 to 0.4 m SLR from Greenland, 1.0 m SLR total. Greenland would still have 93% of its ice. The ablation rate in 2100 would be around 4000 GT/year, compared to 286 GT/year in 2009.
That's still a big increase in ablation over the next 90 years, but much more reasonable than Berényi Péter's calculations above.
Tedesco et al., 2008 . Whereas northern Greenland began a series of substantial melt anomalies in 2005, with 2008 being the record.
Box et al. 2009
This has had implications for the Petermann Glacier in northern Greenland which has the longest floating glacier tongue in the Northern Hemisphere.
Petermann Glacier Retreat
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There has been a lot of speculation that a very large glacier [Pine Island glacier] in Antarctica is unstable. If there's much more melting, it may break off and slip into the ocean. It would be enough to produce an immediate sea-level rise of two metres, something huge, and tsunamis.
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Two meters? Is the PIG really that big? This is the first time I've seen someone provide a number for such an event. Even assuming a fairly large fudge factor, 2 meters of "immediate" SLR is an astounding number.
Source for the above quote: http://www.guardian.co.uk/environment/blog/2010/mar/29/james-lovelock
RealClimate post
Articles:
http://www.sciencemag.org/cgi/content/abstract/291/5505/862
http://tintin.colorado.edu/.../MeierPost_FastTidewaterGl_JGR_1987.pdf
For starters, ice can disappear by evaporation and sublimation resulting from wind blowing over its surface. Of course the predictions of massive sea level rises don't factor in this.
John Daly, who has written a number of books arguing against the alarmist view, has posted temperature data that he obtained from GISS and CRU. He subdivided the data into regions, including the Arctic, and has data from a number of stations located in Greenland.
http://www.john-daly.com/stations/stations.htm
What is interesting is the temperature plots from 1930 onwards from stations located on Greenland show consistent temperatures and no rising temperatures - especially the the heights needed to melt glacial ice.
Here are a few examples:
http://www.john-daly.com/stations/dmkshavn.gif
http://www.john-daly.com/stations/egdesmnd.gif
http://www.john-daly.com/stations/ilulissa.gif
http://www.john-daly.com/stations/janmayen.gif
On another note regarding isostatic recovery, it should be noted that the norther part of North America is still rising. Canadian scientists have noted that while sea levels elsewhere in the world have risen marginally, they have found no signs of similar rising in the Canadian artic. They have concluded that this phenomenon is the result of isostatic recovery. What climate scientists need to take into account is the amount of water being displaced by this isostatic recovery - said water of course flowing into the other oceans and contributing to their rise. In other words, not all of the rise in ocean levels can be attributed to glacial melting.
Finally you have to understand that when glaciers move, they are not melting but are growing. Glacial ice disappears from melting AND evaporation and sublimation.
Since historical Greenland temperatures appear to be somewhat static since the 1930's, and keeping in mid that even if they are warmer than in the past, temperatures still remain sub-zero for most of the year, it is unlikely that any melting of Greenland ice is attributed to higher temperatures brought on by increased levels of atmospheric CO2. Scientists should look elsewhere for the cause if they are serious in trying to determine what is happening there.
Notice how the thinning matches up with the GRACE and GPS data from Kahn paper. So that's three independent datasets (four, if you include prior radar altimetry data).
Thanks for pointing this one out, John. Now to get a copy of that paper for my own post at S&R.
http://earthobservatory.nasa.gov/Newsroom/view.php?id=43080
The ice below the melt line does melt in the boreal summer:
http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=20178
http://earthobservatory.nasa.gov/IOTD/view.php?id=7569
The area experience summer melt is also increasing:
(1) gravity data from GRACE, which yields the total mass balance of the ice sheet;
(2) laser and radar altimetry measurements of ice sheet elevations;
(3) interferometric radar measurements of increases in the velocity of outlet glaciers; and
(4) high-precision geodetic GPS measurements of bedrock and ice elevations.
I'm going to ignore the suggestion that Greenland is losing 300 GT/year of mass (and accelerating) due to "sublimation," since I assume that wasn't serious.
Re: temperature, John Daly is not a reliable source, his graphs don't show data for most of the past decade, and Jan Mayen is not in Greenland.
http://earthobservatory.nasa.gov/IOTD/view.php?id=8010
Melt season anomaly in 2006
http://earthobservatory.nasa.gov/IOTD/view.php?id=7563
And the melt anomaly in 2007:
http://earthobservatory.nasa.gov/IOTD/view.php?id=8264
And in 2008:
http://earthobservatory.nasa.gov/IOTD/view.php?id=37215
This is also quite striking, melting ice reveals new island off coast of Greenland:
http://earthobservatory.nasa.gov/IOTD/view.php?id=7738
http://www.sciencedaily.com/releases/2009/12/091215173144.htm
The isostatic uplift doesn't have to be inferred from relative sea level, it has been measured directly. See Sella et al. (2007) in GRL, or free ftp access (according to Google) at the author's ftp site.
As far as accounting for the effect of isostasy in sea level rise, you need to acquaint yourself with the work of Jerry Mitrovica and colleagues, who have done that (and more).
"Based on the differences he saw between his map and his new observations, he concluded that the surrounding ice had retreated at least 10 kilometers (6 miles) in the previous five years."
An average of 2 km/year. Some should instruct these glaciers to stop being so alarmist, it's starting to look bad.
John L. Daly died in 2004 & the charts you reference have not been updated since 2003, most of them end in 1999 or 2000. Daly's site has been maintained by a colleague, but even that is quite outdated:
http://www.john-daly.com/
NewScientist (13 January 2010) has an article on the potential impact on global SL if the PIG were to slide into the ocean-- they reckon that would increase global SL by about 24 cm.
And yes, scientists think PIG exceeded its tipping point in 1996.....
The exact quote from New Scientist:
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The model suggests that within 100 years, PIG's grounding line could have retreated over 200 kilometres. "Before the retreating grounding line comes to a rest at some unknown point on the inner slope, PIG will have lost 50 per cent of its ice, contributing 24 centimetres to global sea levels," says Richard Hindmarsh of the British Antarctic Survey, who did not participate in the study.
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Source: http://www.newscientist.com/article/dn18383-major-antarctic-glacier-is-past-its-tipping-point.html
I wish people would push Lovelock (and everyone else) harder to back up such pronouncements.
GRACE show it will probably be a record-breaking one!
Perhaps we should listen to the local population:
"A Greenlandic supermarket is stocking locally grown cauliflower, broccoli and cabbage this year for the first time. Eight sheep farmers are growing potatoes commercially. Five more are experimenting with vegetables. And Kenneth Hoeg, the region’s chief agriculture adviser, says he does not see why southern Greenland cannot eventually be full of vegetable farms and viable forests."
" ... Cod, which prefer warmer waters, have started appearing off the coast again. Ewes are having fatter lambs, and more of them every season. The growing season, such as it is, now lasts roughly from mid-May through mid-September, about three weeks longer than a decade ago."
-- http://www.nytimes.com/2007/10/28/world/europe/28greenland.html
Again, evidence of warming that isn't dependent on temperature data.
Wonder if there's any beachfront property available in Narsarsuaq.
For anyone who has worked in the far north in the winter, the sublimation of snow cover is quite observable as is the reduction in ice on the lakes.
Geologists Andrew Fountain, Karen Lweis and Peter Doran authored an article in Global Planetary hange (Vol 22 Issues 1-4) from which I took the following quote:
"In polar regions, where melting is typically absent, sublimation is the only significant process by which glaciers lose mass and its rate largely depends on wind speed rather than temperature."
The reduction in glaciers located in high elevations in Chile and Mount Kilimanjaro etc are attributed to sublimation and not melting.
Observations being made about Greenland and interpretations as to the cause of the change in Mass blaance that are posted here simply have no scientific basis attached to them.
Also, you probably did not notice that the paper you cite refers to closed drainages and has no particular relevance to Greenland or other locations where glaciers or ice sheets are connected to outflows. Sublimation or melting is the only available means of attaining mass balance for glaciers in closed drainages. The Greenland ice sheet and associated glaciers are of course not confined to closed drainages.
Simple fact - any loss from any ice sheet winds up in the ocean. Yes, humans have created some extra lakes with dams, and a warming atmosphere will almost certainly retain more water vapor, but the former is a relatively small (though measured!) effect while the latter is obviously something that an AGW denier isn't going to want to talk about.
You are going to have to do better than a blanket claim that all of the observations being made about Greenland have no scientific basis. On what basis do you make that sweeping claim?
Was there a 1930s Meltdown of Greenland Glaciers? by Adam Herrington
True, it is an undergraduate rersearch paper at the Ohio State University, still, it says something. It also provides plenty of literature on the subject.
So melt anomalies were above normal in the northern section of the ice sheet, but not a record.
With regards to GFW - your view assumes a constant level of water vapor in the atmosphere but in face the water content has increased on average at a rate of 1% per year since 1980 - hence the water resulting from the sublimation of ice fields does not all end up in the ocean.
Everyone seems to assume when glaciers reduce in size it is because they are melting. What I am trying to point out is that in the polar regions and higher elevations, a small increase in average global temperatures will not and cannot melt those glaciers by itself. Something else is at work and we need to look at the other driving forces that affect glaciers to determine just that. Also the disappearance of glaciers at their margins is a normal observation - they disappear in the areas of ablation. Also glaciers move as a result of the build-up of ice in their centers which pushes the underlying ice outwards. When glaciers are retreating, you don't see that movement.
Simply posting maps here showing larger areas of ice loss over a given period of time is meaningless. It certainly is no way near being "Quad Erata Demonstratum".
As for Doug, # 34, my point is the ice loss identified by GRACE is not due to melting. There are other factors at work there - similarly to what is going on in the arctic. Those observations reported do NOT support the theory that man-made CO2 is causing warmer temperatures that are resulting in the disappearance of the Greenland ice.
Also the glaciers in South America and in Africa that have disappeared are not closed systems and their disappearance has been attributed to sublimation and not warmer temperatures.
As I mentioned in a previous post, the thermodynamics required to melt that ice simply from a rise in temperature just are not there. For instance, the energy needed to melt a volume of ice is the same temperature needed to raise the temperature of the resulting water to a 140 F level. With a global temp average increase of under 1 degree over 100 years, you do not need a science degree to figure out that polar ice is not disappearing from that marginal increase in temperature.
One last word on the subject, the IPCC identified in one of its reports that glacial melting has been noticeable since 1970. In fact, geological literature identified glacier melting in the 1930's - well before the recorded increase in CO2 levels as measured in Mauna Loa. In addition, the rising temperatures in the arctic oceans were identified in the 1930's so what were are seeing today started well before 1970.
Just as I find it difficult to accept that climate is being affected by only one factor - the rise in atmospheric CO2, (simply because there are multiple factors at play when it comes to climate), I also find it difficult to accept that the polar ice cap and glaciers are reducing simply due to one factor when there are so many others at play.
Sometimes in science we have to step back and ask ourselves "Does it make sense?" In this case it doesn't make sense to me.
This is not my idea -- it is based on direct observations (visual, time-lapse photos), glacier velocity observations, basic glacier physics, and even seismic recordings.
And nobody here is saying that the ice loss is all due to melting in place, except perhaps those who suggest they don't believe any of this because the ice can't be melting in place.
Of course, nobody here or elsewhere (well, the sane, anyway) has said that every last gram of ice seen to vanish in the past few decades is down to a single factor, so you won't find anybody worthwhile to argue that point with you. What we can say (and I imagine you could model this if you cared to take the time) is that sublimation alone cannot account for the entire loss of mass on the Greenland ice sheet.
As to your speculation about the available amount of extra energy required to produce a phase change of a given mass of water from solid to liquid (melt ice), as an exercise take a look at the summer Arctic sea ice anomaly for any of the past few years and then compute for yourself the additional energy being absorbed by the ocean due to the loss of albedo. In case you don't want to do that work, I'll cut to the denouement, plot spoil and say that where energy arrives counts for a lot; using global temperature change to predict the behavior of ice in a given region is a futile approach.
you might be interested in digging a little deeper. Following van den Broeke et al. 2009, they calculated the overall mass balance (surfaces mass balance SMB minus discharge D) and compared it with GRACE results. The former (SMB-D) compares well with the latter (r=0.99, fig. 1 in the paper). Next they show that from somewhere in the '90s SMB has been increasingly negative and D also increased (fig. 2a). The two mechanisms turn out to be comparable in magnitude.
In fig. 2b you'll find the components of SMB, namely precipitation, runoff and sublimation. Sublimation had almost no part in the balance.
Also very interesting is fig.3 where they quote SMB and D separately for various regions of the ice sheet.
The mainstream scientific view of climate change impacts on the mass balance of the Greenland ice sheet is a model of clarity and consistency (both internal consistency and model-observation consistency).
1. We know CO2 and other greenhouse gases are increasing, and physical models suggest that should lead to warming overall and particularly in the northern hemisphere high latitudes (polar amplification). Observed warming from multiple sources matches this.
2. Physical models of glaciers and ice sheets suggest that this warming should lead to a negative mass balance and loss of ice via both melting (primarily in summer below the equilibrium line) and the accelerated discharge from marine terminating outlet glaciers. Remote sensing data specifically confirm (a) an increase in melting, and (b) an increase in glacier velocity.
3. Other techniques (GRACE, high-precision GPS) confirm the overall negative mass balance that would be expected from the mechanisms in (2) above.
That's a very clear, coherent picture. I'm a bit mystified as to why Geo Guy would write Sometimes in science we have to step back and ask ourselves "Does it make sense?" In this case it doesn't make sense to me. Whereas to me, this topic (Greenland ice sheet) seems quite sensible and straightforward, and trying to introduce other explanations for the observed loss of mass raises more problems:
What mechanism would produce a large and rapidly increasing rate of sublimation in Greenland? What evidence is there for this increase in sublimation? Why would all the remote sensing data on melting and velocity be wrong?
Occam's Razor suggests that the straightforward explanation is preferable to the convoluted and mysterious one.
I'm going to pick on something else. Your ludicrous assertion that "water content [of the entire atmosphere] has increased on average at a rate of 1% per year since 1980" Wrong. Water content of the stratosphere may have done that (see Wikipedia), but not the whole atmosphere. Such an increase in the stratosphere would deprive the ocean of ... wait for it ... less than 0.0025 mm/y. That is of course negligible compared to the 3mm/y rise we currently see, and the glacial contribution to same. There probably has been a small increase in tropospheric water vapor too, but on a similar absolute scale (not % scale). And of course that increase in tropospheric water vapor is predicted as a positive feedback in global warming.
Finally, we know CO2 isn't the only factor, so fighting that position is a complete straw man argument. However CO2 is the "biggest control knob".
Carbon black (aka soot) is known to be an important player in reducing ice albedo, thus contributing to the warming/melting of ice. But even if there was some way to eliminate soot emissions without changing our fossil fuel economy, that would only slow down the warming. (And indeed, there are people working very hard to reduce soot emissions.)
This is wrong. Glaciers retreat when the melting/ablation/calving at their terminus causes more mass loss than is made up by flow. But glaciers are always flowing. If more mass flows out of a section of a glacier than is replaced by new accumulated snow->firn-ice and flow from even higher up, the glacier loses mass in that section. Some glaciers flow very slowly, but given gravity and a slope, any large mass of ice flows downhill.
Does anyone have any insight into what the heck is going on with arctic sea ice extent? Is this just a short term weather phenomenon? It's pretty weird to see this kind of growth in late March. As significant as the mass loss from Greenland has been, I don't think freshwater bergs are contributing that much to sea ice.
Easy come, easy go, maybe. For my part I'm going to reserve any judgment about the health of Arctic ice until much later, August or September. Extent is has been dethroned, seems to me, with volume being the real story now.
But again, I'm speculating.