An interview with Michael Mann on metastable shifts in climate:
Published on Sep 24, 2013
In recognition of climate week, Thom talks with renowned climate scientist Dr. Michael Mann about the dangers of global warming. Dr. Mann in concerned we may be running out of time to rein in global temperatures.
Most of the current models of glacial ice melting (and contribution to sea level rise) focus on ice melting and less than they need to on the process of glaciers falling apart in larger chunks such as ice bergs. Also, current understanding of glacial ice melting due to global warming indicates that the Western Antarctic Ice Sheet (WAIS) is more vulnerable to melting over coming decades or centuries than is the Eastern Antarctic Ice Sheet (EAIS). New research from two different teams seems to provide a major corrective to these assumptions.
First, about how glaciers turn into ocean water.
Consider this experiment. Take a large open-top drum of water and poke a hole near the bottom. Measure the rate at which water comes out of the hole. As the amount of water in the drum goes down, the rate of flow out of the hole will normally decrease because the amount of water pressure behind the hole decreases. Now, have a look at a traditional hourglass, where sand runs from an upper chamber which slowly empties into a lower chamber which slowly fills. If you measure the rate of sand flow through the connecting hole, does it decrease in flow rate because there is, over time, less sand in the upper chamber? I’ll save you the trouble of carrying out the experiment. No, it does not. This is because the movement of sand from the upper to lower parts of an hourglass is an entirely different kind of phenomenon than the flow of water out of the drum. The former is a matter of granular material dynamics, the latter of fluid dynamics.
Jeremy Bassis and Suzanne Jacobs have recently published a study that looks at glacial ice as a granular material, modeling the ice as clumped together ice boulders that interact with each other either by sticking together or, over time, coming apart at fracture lines. This is important because, according to Bassis, about half of the water that continental glaciers provide to the ocean comes in the form of ice melting (with the water running off) but the other half consists of large chunks (icebergs) that come off in a manner that has been very hard to model. By treating the ice as a granular substance, Bassis and Jacobs have been able to look at the relationship between the large scale geometry of glacial ice and the smaller scale process of ice berg calving.
From the abstract of their paper:
…calving is a complex process and previous models of the phenomenon have not reproduced the diverse patterns of iceberg calving observed in nature… Our model treats glacier ice as a granular material made of interacting boulders of ice that are bonded together. Simulations suggest that different calving regimes are controlled by glacier geometry, which controls the stress state within the glacier. We also find that calving is a two- stage process that requires both ice fracture and transport of detached icebergs away from the calving front. … as a result, rapid iceberg discharge is possible in regions where highly crevassed glaciers are grounded deep beneath sea level, indicating portions of Greenland and Antarctica that may be vulnerable to rapid ice loss through catastrophic disintegration.
This is interesting in light of a second recent paper, by Carys Cook and a cast of dozens, which looks at Antarctica during the Pliocene. Green house gas levels were about the same during much of the Pliocene as the current elevated levels, and sea levels may have been many meters higher at various points in time as well. From the abstract of that paper:
Warm intervals within the Pliocene epoch (5.33–2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century and atmospheric CO2 concentrations similar to today. Estimates for global sea level highstands during these times imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica… Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The [geochemistry]… suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene.
This is, to me, one of the most disturbing facts about climate change that we learn from the paleo record. It may be reasonable to say that our near doubling of greenhouse gasses have brought us to a situation in which it is normal to have perhaps something like 20 meters more sea level than we have today, and that the only thing keeping that from happening is … well, nothing, really, other than time. Glaciers tend to behave glacially, after all. Cook et al. look at sediments offshore from Antarctica deposited during the Pliocene periods. Using fingerprinting with specific stable isotopes they were able to determine that at certain times during the Pliocene sediments were being deposited in the ocean from an eroding landscape that is currently deeply and firmly buried under the EAIS. This seems to suggest that under conditions not necessarily very different from today, large areas of Eastern Antarctic, thought to be iced over long term, can be ice-free. If those vast areas were ice free, than the ocean would have been much higher, and it seems that the ocean was, in fact, higher at that time.
I asked Jeremy Bassis, lead author of the ice-as-granular-material paper, if he could translate the modeling work done by him and Jacobs into an estimate of how fast glaciers could disintegrate. He told me that it was hard to say. Their models help them “… understand the different patterns of calving that occur and based on that, it looks like some regions of Antarctica and Greenland might be vulnerable to disintegration. However, the simulations we did took place over a few hours so to translate that into an actual sea level rise estimate we would need to run the models for much longer. The best I can say for sure is that based on our model, important processes are not included in current estimates of sea level rise.” He also noted that most models that don’t use paleo data assume iceberg calving at present rates from their current position at the sea. Their paper, however, suggests that these may not be good assumptions.
Sadly, none of this work will be included in the upcoming IPCC reports. The time cycle for IPCC is rather ponderous, which may be good in some ways, but also has disadvantages. These two papers exemplify an effort to address one of the biggest unknowns in climate change, the nature and character of meltdown of the polar ice caps. We need to put more resources into this sort of study.
Meanwhile, don’t throw away your knickers.
Bassis, J. N., & Jacobs, S. (2013). Diverse calving patterns linked to glacier geometry Nature Geoscience DOI: 10.1038/ngeo1887
Cook, Carys, Flierdt, Tina van de, Williams, Trevor, & et al (2013). Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth Nature Geoscience DOI: 10.1038/ngeo1889
The National Academies Press of the United States has recently released a report that will be of interest to those of you concerned with climate change (which better be every one of you dammit!). The report talks about increasing floods due to weather whiplash and sea level rise due to glacial melting (and subsidence), mainly in relation to the levees program and insurance, but also more generally. Here’s a small excerpt to give you a flavor:
Community flood risk scenarios will continue to evolve as change occurs. Climate change will have a variety of regional impacts, and the geographic location of a community will affect how changing conditions affect risk. Some areas will have more droughts, some will have more frequent floods, and others will have more intense floods. Research to understand these hydrologic changes is ongoing (NRC, 2011, 2012a). A recent special report of the Intergovernmental Panel on Climate Change (IPCC, 2012) indicates a likely increase in many regions of the frequency of heavy precipitation events, and when coupled with increasing vulnerability presents a myriad of challenges for coping with climate-related disastersIPCC. Galloway (2009) cites 11 major international studies conducted from 1987 to 2002 that all predict significant climate change–induced hazards, including increased flooding, higher mean atmospheric temperatures, higher global mean sea levels, increased precipitation, increased strength of storms, more energetic waves, storm surges that reach further inland, undercapacity of urban sewer- age and drainage systems, increased vulnerability of port cities, and disproportionate impacts on disadvantaged population segments (Galloway, 2009). The rise in sea level and the increase in storm surge due to climate change puts many coastal areas at risk from intensified flooding (NRC, 2010).
Hirsch and Ryberg (2012), in examining trends in annual floods at 200 stream-gauge sites in the United States, found that , while there appeared to be no strong statistical evidence for flood magnitudes increasing with increasing global mean carbon dioxide concentration, there were differences in flood magnitudes among the four quadrants of the conterminous United States (Figure 6-8). They indicate that the attention should be paid to the effects of changes in the relative “importance of the role of snowpack and rain on snow events.” Raff (2013) suggests that the increase in magnitude of floods in the northeastern and midwestern United States (Figure 6-9, Upper Right), may have consequences in the Upper Mississippi, Ohio, and Missouri watersheds (Hirsch and Ryberg, 2012; Raff, 2013).
The Draft National Climate Assessment, issued in January 2013 by the National Climate Assessment Develop- ment Advisory Committee, begins with the statement:
Climate change is already affecting the American people. Certain types of weather events have become more frequent and/or intense, including heat waves, heavy downpours, and, in some regions, floods and droughts. . . . The largest increases have occurred in the Northeast, Midwest, and Great Plains, where heavy downpours have exceeded the capacity of infrastructure such as storm drains, and have led to flooding events and accelerated erosion.
The report goes on to point out the increasing vulnerability to flooding of those in floodplains and coastal areas
You can buy the report for a mere $53, or download it for free. (Downloading from the NAP involves signing in and stuff, but it is pretty easy, though at the moment their server is running a bit slow since they just publicized the report and everybody wants a copy of it.)
Go HERE to get the report.
NOTE: I’ve rewritten this post and redone the graphic. The original map on which I based the reconstruction, provided by the USGS, is distinctly different than the one the USGS provides today. The difference is, in fact, rather dramatic. In comparing the older and newer versions of the maps, I have decided to assume the later, more recent, version is more correct. I admit to being a little annoyed at the USGS providing a truly bogus map on their web site, but that is water under the bridge, as it were. So, the following post is edited a bit and a new graphic is provided. Thanks to wehappyfew for pointing out the likely error on the map.
There have been times in the past when there was very little ice trapped in glaciers. During this time, sea levels were higher because that water was in the ocean (most of it, anyway). It has been a long time since then. However, with global warming, more and more glacial ice is returning to the sea and this contributes to sea level rise.
The amount of fossil carbon that needs to be released into the atmosphere to cause most of the glacial ice to melt is not known. We can’t directly use ancient time periods to assess modern sea level rise by measuring the sea levels from those periods because there has been too much other stuff going on in ocean basins and along current coast lines. But, we can estimate that there was very little glacial ice during, for example, the early Eocene, and the transition of Carbon in the atmosphere to the formation of glaciers might be under 800 ppm. So, if we double the current amount of CO2 in the atmosphere, maybe that would melt all the glaciers. There was more methane in the air at that time as well, but we are releasing plenty of methane as we also release Carbon, so that’s not much of a problem. The biggest factor is probably this: The configuration of continents have changed since that time to increase the likelihood of glacial formation at the poles, so returning to some Eocene (or other) atmospheric CO2 value may result in much less melting. But that’s OK, because we can certainly increase the amount of carbon to more than around 800 ppm!
If we release CO2 at approximately modern rates (baed on population size), and have population increase up to a point, thus increasing CO2 release (in other words, do nothing significant to mitigate Carbon release, increase the number of people actively releasing it, and population goes up towards 8 or so billion) we can reach over 1000 ppm by 2300 AD, or sooner. That’s surely enough to melt most of the glaciers except bits and pieces in the coldest regions of Antarctica.
It is estimated (see this web page.) that there is about 80 meters of ocean trapped in glacial ice. There are plenty of web sites out there that allow you to add ocean height to see how coastal regions would change, but the ones I know about don’t go to 80 meters. So, to find out what North America would look like, I found a map that has pixels to indicate altitude, with different colors representing topography, at a fine enough level to work with.
The USGS has a map with color coded topography. There is a color break at 60 meters, which is much less than the maximum possible sea level rise. The next break is at 114 meters. That is higher than sea levels will rise. However, if sea level rises to about 80 meters, it will do so unevenly (it may, for example, be much higher in the Carolinas). Then, as sea level rises, the land will be pushed down various amounts by the weight of the water, so 80 meters might be considered a minimum estimate of rise in some areas. Even more important, I suspect, erosion would cause important changes. If you look at, say, a 60 meter topo line in a region made of something other than hard rock, you have to assume that transgression of the sea including the effects of erosion would move way inland in some cases, beyond that topo line.
So, since we are at present looking for an 80 meter contour line easily located on the right scale map, and we only have 60 and 114, but the real contour line we are probably looking for is higher than 80, we could round UP to 114. But that would almost certainly depict inundation of areas that won’t actually be inundated. So, what I’ve decided to do is to put the ocean at 60 meters, then make a grey area (to reflect, well, this being a grey area!) between 60 meters and 114 meters. With ALL of the ice melted, the shoreline will likely be somewhere in this grey area, probably covering all of it (and more?) along the south coast and probably much less in Maine. Either way, Florida is toast. Wet soggy toast.
Also, I decided to focus in on this map a bit and depict the US east of the Rockies. At this scale, the west coast is fairly uninteresting using this method (the continental margin is right at the coast, so it is very steep). And, the transgression effect, the sea moving laterally across the land after a rise, is probably very locally variable and unpredictable there anyway.
One of the interesting things I discovered is that when defining the zone between 60 and 114 meters, that turns out to be a fairly narrow strip along much of the coast. This is what one would expect if somewhere in that zone is the original high strandline from the last time sea levels were that high (a few million years ago or so). So that’s cool.
This is a VERY ROUGH approximation. Just for fun.
A paper came out in today’s Nature about glacial melting and its contribution to sea level rise. This paper does not present new research, but rather summarizes and evaluates the last several years of research on modeling and measuring contiental glaciers and their dynamics.
From the Abstract:
Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain
There are many difficulties with measuring and understanding the dynamics of melting of large continental glaciers, the large ice sheets that cover Antarctica and Greenland. As ice melts from these glaciers, they grow lighter and this allows the underlying bedrock to rise up, and conversely, if snow is added to the surface this increases the amount of depression of the underlying bedrock. For this reason you can’t just measure the surface of the ice to estimate how much has been added or removed. When ice melts on the surface, some of it travels down into the glacier and some comes right off the surface. The ice that goes into the glacier may cause deeper ice to melt, or it may provide lubrication to the base of moving streams of ice. As a glacier loses mass at the edge through calving of ice bergs, and the margin retreats away from the sea, the degree of calving, which is an ice-ocean interaction effect probably decreases. Large masses of ice are “grounded” at the outer margin on a “grounding line” beyond which is floating glacier (not sea ice, but large masses of ice undercut by the sea). The grounding line can move towards the sea or away from it, and the dynamics of this movement are complex and difficult to model or measure. Many of the Antarctic grounding lines occur on surfaces that slope downwards in the inland direction, which makes the dynamic a bit more complicated to measure.
Major changes that have improved estimates include adding dimensions to some of the models, such as considering both vertical and horizontal forces along grounding lines. Also, newer models use a finer resolution. However, the increase in resolution is thought to be insufficient; current models are not calculated at fine enough resolution to include numerous smaller ice streams that are narrower than the sampling density of the models.
It appears that the range of uncertainty of ice-melting models has improved significantly over the years so greater confidence in their predictions may be warranted. The best estimates of future contribution to sea level rise of melting glaciers is still highly variable, however.
The current estimates of contributions to sea level rise in mm per year from various studies are between 0.59 and 0.82 from the major ice sheets, between 0.71 and 1.4 for ice caps and glaciers, about 1.1 for thermal expansion, and a negligible but positive amount from changes in terrestrial water storage. These modeled amounts sum to 1.66 mm per year or 3.11 mm per year depending on the set of sources that are used. The observed change in sea level rise over the period from 1993=2008 is 3.22, so there is good agreement though the models are a bit light.
These numbers are small, but they are larger than previous estimates and observations. Still, compared to the potential sea level rise when one considers that the ice in the continental glaciers equals several meters of ocean water, near future sea level rise may be expected to be relatively low if these models are correct and account for everything. Over a century of time, this amounts to about 300 mm, or one foot, of sea level rise. If, however, oceans are warming more than the air at present and a few more episodes of that occur over the next century, this may be considered a minimal estimate. One foot does not sound like a lot of sea level rise, but it is enough to remove extant barrier beaches. Also, flood tides would not be increased by one foot, but rather, more exponentially. This is how a sea level rise of about this order of magnitude over the last century managed to contribute to the flooding of the lower Manhattan subway tunnels when the region was struck by Hurricane Sandy last year.
But there is a problem. Several areas of uncertainty exist in the models that are currently in use, and my impression is that these areas of uncertainty could be associated with dramatic errors in sea level rise estimate. The dynamics of grounding line changes, the role of lubrication at the base of glaciers (which can cause ice streams to speed up on their way to the sea) and the effects of warm currents shifting their position in Antarctic to cause more melt at the boundaries are among those factors that are least known and that have the highest uncertainty. Also, the seaward edge of continental glaciers are not only held in place by their grounding line on the continent, but also by more distal parts of the floating segment of the glaciers being pinned on prominence. As far as I know the effects of pinning being disrupted or lost are not included in any of the models. Also, I’m pretty sure that the effects of sea level rise on grounding and pinning have not been adequately addressed.
That these issues may be a problem is empirically suggested. The paleo-record shows that continental ice melting and associated sea level rise may occur in fits and starts, with steady melting punctuated by brief periods of extreme melting. The current models don’t seem to predict this sort of event, though these events probably happen.
Hanna, E., Navarro, F., Pattyn, F., Domingues, C., Fettweis, X., Ivins, E., Nicholls, R., Ritz, C., Smith, B., Tulaczyk, S., Whitehouse, P., & Zwally, H. (2013). Ice-sheet mass balance and climate change Nature, 498 (7452), 51–59 DOI: 10.1038/nature12238
Photo Credit: christine zenino via Compfight cc
You’ve all heard about the horrible tragedy in Bangladesh, still unfolding. Not to distract from that event, or diminish its importance, I thought it would be interesting to have a look at that low lying country in relation to long term sea level rise caused by climate change. I am making no claim here about the maximum rate of sea level rise or about the timing of sea level rise. But the truth is, there have been times in the past when there was virtually no year round ice (glaciers) anywhere on this planet, and sea levels were much higher than they are now. During a time period not too different from the present (probably not as warm, or just about the same) sea levels were several meters (maybe about 6 meters) higher than they are now, suggesting that even under current conditions a lot of the ice in Greenland and Antarctica could melt. In other words, there is an argument that even if we curtail global warming now and keep things at their current somewhat warmed up level ice may continue to melt enough to raise the sea by meters. If we continue to warm the atmosphere and the oceans, the total sea level rise could be much, much higher.
Using the interactive map here, let’s look at Dhaka, the site of the recent and ongoing tragedy in Bangladesh. This is appropriate because it is the first world thirst for goods and luxury that produces both sweat shops like the one that just collapsed, killing hundreds of workers, and that produces global warming that will also produce catastrophic sea level rise.
Here’s a map of the area now, showing the local terrain:
If the entire Greenland Ice Sheet melted (but nothing else), or if a bunch of Greenland and a bunch of Antarctica melted, to produce about 7 meters of sea level rise, this is what the map would look like:
This is not what the region would look like, actually. The sediment here is all soft delta material what would be eroded away horizontally in no time. Another way to think about this is that if the sea went up just a meter or two, this entire region would probably be eaten away by horizontal erosion very quickly. Anyway, let’s add some more water and see what this first approximation would look like. Imagine if the West Antarctic and Greenland ice sheets both contributed maximally to sea level rise. This would be the minimal result:
If all the glacial ice in the world melted, and sea levels rose to the maximum height they’ve ever been, our closeup look of the region would look like this:
As you probably know, Bangladesh is one of the lowest elevation larger countries in the world. In fact, it seems like Bangladesh is defined almost entirely by its topography; Bangladesh is the delta. If we take the same maximal sea level rise as in the last graph, and step back a ways to see the effect at large scale, this is what we get:
By the way, there’s a cool book coming out on the topic, Rising Seas: Past, Present, Future
Photo Credit: joiseyshowaa via Compfight cc
According to some estimates, if sea levels rose one meter, Boston would lose 3% of it’s land surface, Washington DC a mere 1%. Tampa and Miami would lose 18% and 15% respectively. New Orleans would lose 91%.
A six meter rise would result in much larger losses. Norfolk, Virginia and Miami Florida would be essentially gone.
These estimates use the assumption that the sea level rises in those areas vertically, and the corresponding topographical level in the coastal city becomes the shoreline. They don’t account for the fact that the ocean does not work that way. (see Sea Level Rise…Extreme History, Uncertain Future.)The shore of the ocean normally consists of a relatively flat zone covered by sea (perhaps exposed ~2 times a day at low tide), a steeper zone where the sea intercepts the land (and generally goes up and down a certain amount with the tides) which was carved out by erosion, then inland, whatever topography would have been present prior to the incursion of the sea. The original shorline first contacted by the sea is gone, and the strandline has moved, or transgressed (that’s the term we use), some distance across the landscape. In a place like Miami, the sea may transgress many miles across relatively easily eroded sediment. In a place like Boston, filled land (which makes up a huge amount of that city’s land surface) might be easily eroded away, glacial sediments that make up much of the city’s substrate would erode fairly quickly. Rock conglomerates that make up much of the southern part of the city would erode slowly while weathered argilite underneath Cambridge would be eroded away quickly. The North Shore communities, sitting on hard rhyolite, would make nice islands for a long time. In other words, it would be complicated. Continue reading How much can the sea level go up with global warming and how fast will it happen?
Rising Sea Levels: An Introduction to Cause and Impact
To me, sea level is one of the most interesting and important of climate related issues. Interesting because I’ve done archaeology at the edge of the sea, sometimes beneath it, sometimes racing ahead of it, and often, looking at changes in human settlement caused by its rise since the Last Glacial Maximum. Important because one of the most fundamental variables in human land use patterns is, well, where the land is (and isn’t), and that is defined in large part by where the sea is (and isn’t)!
Janin and Mandia acknowledge that the last few thousand years of human development and history occurred during a period of little or no sea level change, but now, sea level rise is a factor. They address the relationship between climate change, the hydrologic cycle, and sea level rise, discuss storm surges (very relevant to those in the northeastern US on this fine Thursday morning after the Superstorm) and the relationship between sea level and glacial ice (or lack thereof). The book is mostly organized geographically, with major chapters looking at each ocean basin forming the core of the work, flanked by background information, science, theory, and overviews of sea level rise impact and an introduction to who is whom in the field of climate change rise. There is an appendix chock full of cool stuff.
Of New York City, the authors note:
New York City has a watery past and will have a watery future. It is situated at the mouth of the Hudson River in southeastern New York State and has a fine, deep, naturally-sheltered harbor which was the keystone of its prosperity. … The city today is vulnerable to storm surges from winter Nor’Easters … and from summer hurricanes, as well as from the prospect of sea level rise. Much of the metropolitan region is less than 16 feet (4.8 meters) above mean sea level. It is estimated that, by the 2050s, adding as little as 1.5 feet (0.46 meters) of sea level rise to the forecast storm surges from a Category 3 hurricane which follows a worst-case track would cause extensive flooding in many parts of New York City…. areas subject to flooding would include the Rockaways, Coney Island, much of southern Brooklyn and ?Queens, portions of Long Island City, Astoria, Flushing Meadows-Corona Park, lower Manhattan, and eastern Staten Island from Great Kills Harbor north to the Verrazano Bridge.
Which is pretty much what happened on Monday night, without too much sea level rise having happened yet. Obviously, this book is important…
We are becoming aware of two very important changes in the Arctic that you need to know about. These are separate thing but related, and both are almost certainly the outcome of anthropogenic global warming (AGW). They are:
Every summer the large areas of the Arctic Sea’s ice melts away, then it refreezes each winter. The minimum extent of ice is typically reached in about mid September. The extent of ice at this minimum has been getting steadily less over time. Direct and accurate measurements don’t go back far enough to track the effects of AGW over the entire time this has been happening, but we can pretty easily look at the last few decades. Have a look at this graph:
Note that the total amount of sea ice in an average year in the 2000’s decade is about one third less than the total amount of ice in the 1980s, at the minimum period in September. Below the 2000’s line are plotted the three most ice-free years in the dataset; those are the extreme years. The present year, 2012, is tracked through mid-August on this graph.
The present year, 2012, is on track for breaking all records for the Arctic Sea ice minimum.
Here’s an interesting side story. Notice how the red line for 2012 is much straighter in a downward direction than the other lines for the same time period for the last several days of measurement. My understanding is that large storms in the Arctic appeared, covering the sea ice from observation for several days, and when the storms cleared a whole bunch of the ice was gone. This is not that unusual. Storms hasten the disappearance of sea ice. But this was a more dramatic than typical example of this event.
In case you were wondering if it was storminess and not AGW that is causing this year’s ice to be less than the other years, and I’m sure that climate change deniers will make this claim, keep in mind that a) this recent storminess does not explain more than a small amount of the ice reduction compared to overall melting and b) AGW has caused there to be more storminess in the Arctic and more warmth in the Arctic.
Before getting to the really big news from Greenland, I want to first remind you of an interesting event that happened in July, reported by NASA (I mentioned it here). Every summer, some of the ice melts on the surface of Greenland’s massive glacier, then much of that refreezes. However, the melting is usually spotty…here and there and rarely everywhere. The highlands are too cold to melt at all in some years. But July was very warm and there were a few days when virtually the entire surface of greenland melted. There were slushy puddles everywhere. Then, much of it refroze. This happens now and then. We can assume that widespread melting like this is more common in a warmer world, and will be part of the process of glacial wasting as the Greenland Ice Sheet turns over time into seawater. But this particular event was in and of itself not entirely unheard of.
But there is a neat graph that shows why glacial melting is both more important than one might thing and also more complicated than one might think. Have a look:
Just as sea ice extent in the Arctic reduces every summer, the albedo of the Greenland Ice sheet reduces. The white fresh frozen snow that falls over the winter is highly reflective…has a high albedo…and as it melts and gets slushy and mixes with water is has lower albedo. Plain water has very low albedo compared to snow. This is important because high albedo surfaces reflect a lot of sunlight (which provides heat) back into space while low albedo surfaces absorb sunlight, converting it to heat that adds to the local and ultimately global temperature.
There is a feedback mechanism at work here. Imagine that something happens to make for a late Canadian winter with a widespread heavy snow storms much later than usual. This could be caused by a combination of events happening just right in a given year. So, late in the spring there is a lot more snow cover than normal. This snow will reflect a lot of sunlight away so the beginning of the summer is cooler. If this effect lasts into fall, early snows may cause the subsequent winter to be even colder and snow to fall instead of rain, producing more Albedo. Etc. Conversely, something that reduces albedo in a given year may cause more melting of snow and ice, which means less albedo, and thus more melting. You get the picture.
In the days before we understood Orbital Geometry and before we had a very good ida of how air and sea currents really work, this feedback effect with albedo was considered as a candidate for what causes glacial periods to come on and go away. We now know that albedo related forcing and feedback is not the prime mover in climate change, but it is still an effect.
In the graph above, you see the line for the present year. Note that Greenland albedo is lower for the entire year than for any of the other years plotted. Then, in July, that melting event occurs. Then, the water freezes. Albedo is not like sea ice extent (compare to the two graphs). Sea ice extent is a slowly changing ponderous slow moving variable, while Albedo is al wiggly-wobbly and highly variable. A big snow storm, albedo goes up. A big rain storm, albedo goes down. So, the wobbliness of the line does not mean too much, but it is very cool to see the direct relationship between observed widespread melting and albedo. And, this effect will probably play a role as the Greenland Ice Sheet melts away.
The really big new that is coming out today is about greenland. From a press release covering the findings of Mardo Tedesco, professor of Earth and atmospheric sciences at The City College of New York:
Melting over the Greenland ice sheet shattered the seasonal record on August 8 – a full four weeks before the close of the melting season…
This year, cumulative melting in the first week in August had already exceeded the record of 2010, taken over a full season
“With more yet to come in August, this year’s overall melting will fall way above the old records. That’s a goliath year – the greatest melt since satellite recording began in 1979.” …
This spells a change for the face of southern Greenland, he added, with the ice sheet thinning at its edges and lakes on top of glaciers proliferating.
Professor Tedesco noted that these changes jibe with what most of the models predict – the difference is how quickly this seems to be happening.
To quantify the changes, he calculated the duration and extent of melting throughout the season across the whole ice sheet, using data collected by microwave satellite sensors.
This ‘cumulative melting index’ can be seen as a measure of the ‘strength’ of the melting season: the higher the index, the more melting has occurred.
…
This year, Greenland experienced extreme melting in nearly every region – the west, northwest and northeast of the continent – but especially at high elevations. In most years, the ice and snow at high elevations in southern Greenland melt for a few days at most. This year it has already gone on for two months.
Here’s the graph showing the relative amount of ice melt per year in Greenland for the last few decades.
Stay tuned. And buy knickers.
Professor Tedesco’s Web Site is here.
Source Material (other than the press release):
Arctic Sea Ice Monitor
Sea Level Rise and Ice Melt
Satellites see Unprecedented Greenland Ice Sheet Melt
Albedo update for 2012