Dr. Jeff Masters' WunderBlog

Greenland's greenhouse

Posted by: Dr. Jeff Masters, 8:23 PM GMT on February 22, 2006

Glaciers in southern Greenland are flowing 30% to 210% faster then they were ten years ago, and the overall amount of ice dumped into the sea from Greenland increased from 90 cubic km in 1996 to 224 cubic km in 2005, up 250%. As a result, Greenland's contribution to average annual sea rise increased from .23 mm/year in 1996 to .57 mm/year in 2005, and now accounts for between 20% and 38% of the observed yearly global sea level rise. Two-thirds of Greenland's contribution (.38 mm/yr) was due to glacier dynamics (chunks of ice breaking off and melting), and one-third (.19 mm/yr) from melting. These were the results of a paper called "Changes in the Velocity Structure of the Greenland Ice Sheet" published last Friday in Science magazine. NASA scientist Eric Rignot and University of Kansas researcher Pannir Kanagaratnam used ten years of satellite radar interferometry data to arrive at their conclusions.

The authors attributed the speedier glacier flow in southeast Greenland to climate warming, and noted that there had been a 3° C rise in temperature in the past 20 years at one station there. Widespread glacier acceleration affected just the southern tip of Greenland south of 66° north between 1996 and 2000, then spread rapidly northwards to 70° north by 2005 to cover the southern half of Greenland. The authors anticipated that as glacier acceleration continued to spread northward, Greenland's contribution to global sea level rise would continue to increase in coming years.

Greenland's increase in glacier speed and a corresponding rise in global sea level are reason for great concern, since Greenland holds enough ice to raise global sea level by over 20 feet (6.5 meters), should the ice cap disintegrate. However, the paper does not discuss many complicating factors, and it is uncertain if the paper's findings mean that Greenland's ice cap is in immediate danger. The most worrying aspect of the paper's findings is that we are told that the computer models used to estimate how long it will take Greenland's ice will melt are significantly in error--and in the wrong direction!

Figure 1. Change in sea level from 1993 to the end of 2004 shows a steady increase of about 3 mm/year. No acceleration of sea level rise due to increased input from Greenland or other causes is apparent. Image credit: University of Colorado.

Is the new Greenland melting evident in global sea level trends?
Sea level is a surprisingly difficult thing to measure. Tide gauges are very noisy, and only show sea level trend for the coastal areas they happen to be installed on. Global sea level trends from these gauges show a rise of between 1.5 and 2.1 mm/yr for the period 1950-2000. Satellite data from the TOPEX/POSEIDON and JASON satellites can give a better global picture, and show a rise of 2.9 mm/yr for the period 1993-2004 (Figure 1). This had increased to 3.4 mm/year for the period 1993-2007. The reason for the disagreement between the tide gauges and satellite data is unknown. There is a lot of variability in the data, due to changes in evaporation and precipitation related to such events as El Niño and La Niña. Indeed, sea level is not rising everywhere. In Scandinavia, the land is still rebounding from the Ice Age, and local sea level is receding. Sea level is also not increasing in the South Pacific's Vanuatu Islands, which Michael Crichton focuses on in his State of Fear book. This lack of sea level rise is not well understood, but may in part due to regional ocean current and precipitation patterns that reduce the amount of sea level rise one might expect. Mitrovica et.al. (2001) argue that as an ice sheet melts, the gravitational pull of the ice sheet on the surrounding ocean decreases, so that a substantial melting of the Greenland ice sheet would result in substantial drop in sea level over the North Atlantic, and a major sea level rise over the South Pacific with the maximum rise near the southern part of South America.

Given how noisy the global sea level data is, it should be no surprise that an increasing trend in sea level due to the increased contribution from Greenland is not apparent in Figure 1. According to Rignot and Kanagaratnam, Greenland's contribution to global sea level rise increased from .23 mm/year in 1996 to .57 mm/year in 2005, an increase of .34 mm/year. This is less than the error bounds of .4 mm/yr in the Figure 1 satellite data. It is also worth noting that while Rignot and Kanagaratnam's estimates to contributions to sea level rise due to glacier flow (.38 mm/yr) are not disputed by other studies, their estimate of the amount of melting Greenland is undergoing (.19 mm/yr) is in dispute. For example, Box et al. (2004) came up with a global sea level rise of 1.5 mm/yr due to Greenland's contributions, and Chylek et. al. (2004) say that the ice sheet may not be adding to sea level rise at all.

Figure 2. Average temperatures for the two stations in Greenland with a century-long record. Top: Godthab. Bottom: Angmagssalik. Image credit: NASA Goddard.

Is Greenland's Ice Cap in danger of disintegrating?
Greenland's ice cap is probably not in immediate danger of disintegrating, if temperatures stay at their current levels. Most of Greenland has been in a cooling trend over much of the last 60 years. It is only during the past ten years that we have seen a sharp upward jump in the temperatures at many (but not all) Greenland locations. However, temperatures as warm as Greenland is seeing now were also observed back in the Medieval Warm Period of 800-1300 A.D., and again in the 1930s. We can see the warm period of the 1930's reflected in the temperature records for two Greenland stations with records extending back over a century (Figure 2). Presumably, Greenland's glaciers at that time accelerated to speeds similar to what we are seeing today, without the ice cap suffering significant disintegration. I haven't looked for records of glacier flow and iceberg calving for that time period to check this hypothesis; I doubt reliable records exist.

Natural Variability
The temperature plot of Figure 2 demonstrates that Greenland is subject to large decades-long changes in its climate due to natural variation. The 2-4° C increase in temperature during the 1920s must have been primarily due to natural causes, since human-emitted greenhouse gases were relatively low then. Research results show that the climate of Greenland is dominated by a regional weather pattern called the North Atlantic Oscillation (NAO). The NAO oscillates unpredictably between a negative phase and a positive phase. If the wintertime NAO is negative, the persistent low-pressure area near Iceland called the Icelandic Low moves towards the southern tip of Greenland, bringing a sharp increase in precipitation and warmer temperatures to the island. During the positive phase of the NAO, the Icelandic Low moves back towards Iceland, allowing colder and drier conditions to prevail over Greenland. The wintertime NAO during 1950-2000 was primarily positive, which led to cooling over virtually all of Greenland--the opposite of the global warming trend of most of the rest of the world (Chylek et al., 2004). This cooling reduced the amount of glacier break-up and melting one would have expected due to global warming. To make things more complicated, increased precipitation during the wintertime negative NAO phase tends to add mass to the ice sheet in the interior, and may partially or totally offset the mass loss due to melting from that phase's increased temperatures (Johannessen, 2005). This is a very complicated system with many unknowns! The question--which was not discussed in Rignot and Kanagaratnam's paper--is, how will the expected rise in global temperatures of 1.5 to 4.5° C this century affect the NAO, and thus Greenland's temperature and precipitation? The current consensus from the computer models is that global warming should act to create a more positive NAO, which would keep Greenland cooler and drier.

When will Greenland's Ice Cap be gone?
The consensus view (Gregory et. al, 2004), using computer models that treat the Greenland ice sheet as a static hunk of ice, has been that the Greenland ice sheet will melt in about a thousand years, if atmospheric CO2 doubles. However, the doubling in glacier flow observed in the past ten years comes as a major shock. The models used to come up with the 1000 year estimate do not account for changes in glacier speed at all! The unexpected increase in glacier flow probably occurred in response to the lubrication effect of melt-water penetrating down to the glacial bed, as well as other poorly-understood processes. The paper concluded: "Current models used to project the contribution to sea level from the Greenland Ice Sheet in a changing climate do not include such physical processes and hence do not account for the effect of glacier dynamics." In other words, the models were wrong. Climate change skeptics are find of criticizing computer models, and cite their inadequacy as grounds for dismissing the threat of climate change. Well, it works both ways. Climate change models can be off in the wrong direction--as we also saw with the Antarctic ozone hole, which was completely missed by the models. These new results imply that if Greenland warms significantly (at least 3° degrees C), Greenland's ice could melt in a few centuries, not 1000 years. With 20 feet of sea level rise locked up in its ice, sea level rises well beyond the capability of humans to handle could occur later this century. The real test of the stability of the Greenland Ice Sheet will come when we reach temperatures not seen since before the last ice age, 125,000 years ago. Warm temperatures then caused the Greenland Ice Sheet to mostly disintegrate, leading to perhaps 14-17 feet (4.5-5 meters) of sea level rise (Cuffey and Marshall, 2000). The likelihood of this scenario is highly uncertain, though, given our lack of understanding of the system, the high amount of natural variability, and the limited amount of historical data we have to look at.

One interesting political note
Rignot works for NASA, which has recently been embroiled in controversy over whether political appointees there had tried to silence NASA climate scientist Jim Hansen from voicing his opinions. According to Time Magazine, when Rignot was asked if anyone at NASA had tried to shut him up, he said he had not been subjected to any such pressure.

The University of Colorado has a nice image showing where Greenland melted in 2005, and which areas melted for the first time.

Jeff Masters

References
Box, J.E., D.H. Bromwich, and L-S Bai, 2004. Greenland ice sheet surface mass balance 1991-2000: Application of Polar MM5 mesoscale model and in situ data. J. Geophys. Res., 109, D16105, doi:10.1029/2003JD004451.

Chylek, P, J.E. Box, and G. Lesins, "Global Warming and the Greenland Ice Sheet", Climatic Change 63:, 201-204, 2004.

Gregory, J.M., Huybrechtsm, P., and Sarah C. B. Raper, "Threatened loss of the Greenland ice-sheet", Nature 428, 616 (8 April 2004) | doi:10.1038/428616.

Johannessen, O.M., et. al, "Recent Ice-Sheet Growth in the Interior of Greenland", Science, 310: 1013-1016, 11 November 2005; published online 20 October 2005 [DOI: 10.1126/science.1115356]

Cuffey, K.M., and S.J. Marshall, "Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet," Nature, 404, 591-594 (2000).

Mitrovica, J.X., Tamislea, M.E., Davis, J.L., and G.A. Milne, "Recent Mass Balance of Polar Ice Sheets Inferred from Patterns of Global Seas-Level Change", Nature 409, 1026-1029, 2001.

Categories: Climate Change Glaciers

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101. HurricaneMyles 5:22 AM GMT on February 24, 2006
DenverMark, No one really knows that answer to those questions you propose. Everyone talks about lower albedo from less ice, but I've seen reports that we are actually increasing albedo and reflecting more energy then before. Strange, huh? Now it could be an outdated report these days, but this was only a few months ago, If I remember correctly. All people can really do is speculate about changes global warming will cause. The warming could end up being a good thing, unlocking millions of acres that were once covered by ice without causing the massive problems some people expect closer to the equator. Or the opposite could happen; It warms to such an extent that we have severe climate change resulting in radically different weather for areas of the world. This change could result in jet streams that are much father north, allowing tropical systems to form year round in the Atlantic and other basins in the world. Drought could plague areas and cause desserts to expand rapidly. Or we could have another scenario; the melting of the ice caps in both the Artic and Antartic, cause a major change in salinity levels in the ocean resulting in the shutting down and reorganizing of the currents worldwide. During the shutdown of currents we would most likely dive head first into an ice age since heat would be locked at the equator and not be brought up to the mid-latitudes. After the currents reorganized anything could happen as far as climate change goes. Or the warming could stop tomorrow. Unlikely, but still possible in every sense. Since we really dont understand completely what is driving global warming(some would say its pure C02, but that it arrogant and irresponsible, IMO, to act like we have a complete understanding of our environment) so we cant rule it out that tomorrow, or next week, or next year, that the climate wont stop warming and start a cooling trend, or even just moderate for a decade or more. We really just dont know because we have dont know all the variables and we dont know how strong the relationships are between the variables and changes in the climate. Member Since: January 12, 2006 Posts: 5 Comments: 827

103. F5 5:41 AM GMT on February 24, 2006
Snowboy, Seeing what goes into the models doesn't make them more accurate. In the programming world, we say GIGO...Garbage in, garbage out. It has been pointed out repeatedly that their assumptions regarding temperature as well as CO2 levels are incorrect. In addition, they use a "fudge factor" as an input based on outputs of various ensemble models, in order to correlate their data. In addition, given the seeming inability to understand the workings of the various factors both stand-alone as well as in concert should make anymore MORE skeptical about pinning the current warming on any particular variable. CO2 is an easy target, but that doesn't mean there is causality. Even if over a 50 year period, they were in agreement, it still wouldn't mean that another factor or factors combined wasn't responsible. And if your model is designed to detect what different levels of CO2 in the atmosphere will do to temperatures, is it any wonder what the response is when they add additional CO2 to the model. Given that CO2 isn't even all that great a GHG, one wonders what all the fuss is about. Methane in the atmosphere is a much higher GHG than CO2, as is wator vapor. Given that they've recently discovered that plants produce a lot more methane than previously known, how is that handled in these "models"? What about albedo, land-use changes, coulds, solar radiation, sunspots, earth distance/angle from sun, cosmic rays, amongst other known variables. Are the models initializing and properly handling the role of all of those components. What about when they act together, do the models handle all that as well? Given that they are not well-understand yet, it would be an unbelievably low percentage likelihood that they are. That is why I discount the minute warming that has occurred, and why I have little faith in models as predictors. As for what we hear in the states, we hear the same thing over and over again. The sky is falling, we are at a tipping point, yada yada yada. You rarely, if ever, hear the opposing side. You have to dig for the information, but it's out there, and trust me, I read as much of it as I can, so I counter-balance to some degree all the gloom and doom that's spread about. You want a real statistic... Since February 16, 2005, the Kyoto Protocol has cost US$ 153,280,606,906 while potentially saving an undetectable 0.001589577 �C by the year 2050. Malaria cost US$ 134,295,730,776 in lost GDP and 2,759,050 lives over the same period. And an article on the subject Denying that there is an issue won't make it go away... High cost of malaria

104. snowboy 6:03 AM GMT on February 24, 2006
F5, those arguments are great if you want to shoot down the models. It's like shooting the messenger. But what if (despite the imperfections of the models) the message is true? I have not seen any serious climatologist putting forward other theories or explanations to explain the warming that has been occurring over the past 120 years (since the start of the Industrial Age). btw, I agree that malaria is a huge problem which should be getting much more attention. But if you're going to get onto the subject of misallocation of resources, there much more being spent on much more dubious things than combatting climate change (eg. military spending comes to mind...). And I'm curious, how is it that the US which hasn't signed onto the Kyoto Protocol has managed to spend $153 billion on it? Member Since: September 21, 2005 Posts: 10 Comments: 2546

105. F5 6:04 AM GMT on February 24, 2006
Sorry, should have been "clouds", not "coulds"

107. F5 6:25 AM GMT on February 24, 2006
Well, if you would go read the link you would understand. It didn't state that the US spent that much, it said that the total spent on Kyoto was that much in US dollars. And if you aren't finding other serious climatologists putting forthe other hypothesis, then you aren't looking very hard. Go read the blogs at Climate Science at CSU. Dr. Roger Pielke Sr. is a serious climatologist and there are links on the blog pages to the latest studies. The information is there "if you really want to find it." Here's a link to issues with the climate models.. Climate Models Read away...

108. F5 6:28 AM GMT on February 24, 2006
MichaelSTL, It wouldn't take hundreds of billions to prevent HIV/AIDS infections, since as you state, it's mostly a behavioral issue. To combat malaria though, you need to control mosquitos, which pretty much requires DDT. Unfortunately, the western world has basically told Africa and other areas where malaria thrives they can go pound sand. Use DDT and we cut off aid money. This despite the fact that the dangers surrounding DDT were vastly overstated. But we are willing to condemn millions of people to die for it.

110. DenverMark 1:52 PM GMT on February 24, 2006
Good morning,everyone - A good discussion here. I value everyone's view on global warming. My view has always been that since we don't know how much of the warming trend is due to human activities, we should be taking prudent steps to reduce fossil fuel use and develop alternative energy without taking extreme measures that would damage the world economy. I still hold to the view that oil prices will rise so much in the next 10-15 years, that action will be taken. Snowboy - I think Canadians do have some valid complaints with the U.S.,especially with pollution from the Midwestern states going up to Ontario and Quebec. Also with the U.S expecting Canada to tear up large areas in Alberta with the oil sands so we can have more oil. Many Americans do care about the GW issue and get frustrated with the politics,etc. F5 - I appreciate your countering views to the usual wisdom that it's all or mostly CO2 emissions that are causing the warming. That's why we shouldn't take drastic measures that we may regret later. Also, global warming hasn't killed very many people yet. Bad as the death toll has been from some of the 'canes in the last few years, it doesn't begin to compare with malaria or HIV/AIDS. We must consider what is the most serious issue facing us. Hurricane Myles - That's what's so important, we don't really know what will happen. That's why I don't like the doomsday scenarios and hype that some people go for. Few seem to consider that GW may be more beneficial than harmful. Have a great day everyone! Member Since: February 11, 2006 Posts: 125 Comments: 6988

111. Cregnebaa 3:01 PM GMT on February 24, 2006
I agree lots of other issues are more pressing and do not get the full attention they need like Aids/ Malaria, but also genocide and famine, which could be prevented. Look at the close to 1 million people killed in Rwanda when the world turned the other way. Namibia has 21% of it�s population having AIDS. Botswana a staggering 37.3%. The sad fact is these tragedies are occurring to poorer nations, and the richer developed nations will always focus on it�s own problems, that is human nature, look after your own. That is why Global warming gets so much attention and rising sea levels will affect us. Namibia has 21% of it�s population having AIDS. Botswana a staggering 37.3%. Member Since: October 19, 2005 Posts: 6 Comments: 322

112. Inyo 5:56 PM GMT on February 24, 2006
DDT does indeed cause huge impacts, killing off huge chunks of the fish and bird populations. Now you can argue that 'humans are more important' than fish or birds but nevertheless, the impact is great. I have a REALLY hard time believing that the ONLY way to control mosquitos is DDT. If we really cared about other countries, i agree that rather than just banning DDT we should help them combat the problem using other solutions. But saying 'you HAVE To massively dump this toxin everywhere or you will die of malaria' is a silly scare tactic imho (been reading too much Crichton?) and there are sure to be much better solutions. Also as people are dying in the third world country mainly due to sanitation problems, poverty, and overpopulation, even curing malaria tomorrow wouldnt fix these problems. The solutions are much more complex than just dumping DDT everywhere.. I don't claim to know all the answers, but i know a mistake when i see one. and i reject the 'we can EITHER stop global warming or malarua' argument... this is from the same train of thought of politicials who take a million or two dollars from the Park Service to pay for schools (or visa versa) and then pull the whole 'but think of the CHILDREN' bull poop.... while meanwhile they are spending billions and billions of dollars on other causes which seem much less worthy. back to weather.. to the person who said warming would shift the jet stream north: what is the logic behind this? The circulation patterns that feed the jet stream are driven by temperature differences not by pure temperatures. also, -most models predict wetter conditions in southern California after warming, which is inconsistent with a further north jet stream -El Nino, which results in net warming, actually brings the jet stream south or strengthens the southern jet stream. La Nina, associated with colder than average temperatures, forces it north. I know that El Nino only occurs on one part fo the ocean, but it is linked to warmer worldwide temperatuers (when El Nino occurs, the world average goes up a bit) Member Since: September 3, 2002 Posts: 42 Comments: 765

113. Snowfire 6:04 PM GMT on February 24, 2006
Those who think that rapid climate change is only a US problem or a First World problem are sadly mistaken. Think of the several hundred thousand destitute individuals living in the Ganges Delta of Bangladesh, only a foot or two above sea level. What happens when their land simply disappears beneath the waves? Think about the subsistence farmers and pastoralists of Sahelian Africa. What happens to them when the Sahara expands southward, swallowing up their fields and pastures? I could go on and on. These hapless individuals do not even have solvent or competent governments to look after their needs. Yes, they have other terrible burdens to bear already; but this is all the more reason not to take their vulnerability to climate change lightly. Member Since: June 29, 2005 Posts: 24 Comments: 301

115. HurricaneMyles 6:09 PM GMT on February 24, 2006
Inyo, I was simply stating scenarios. Look at my post again. I never said any of that would actually happen, just that any of those scenarios are plausible because we dont understand the Earth's climate well enough to rule them out. In fact, what I was doing the most was stating the extreme scenarios that lots of people predict. Ala, no real problems, just less ice; servere warming with lots of hurricanes; ice age; and its natural and will stop. Any of that could happen because we really dont know whats going on. Member Since: January 12, 2006 Posts: 5 Comments: 827

116. F5 6:54 PM GMT on February 24, 2006
Inyo, I suggest you read the following links before you trash DDT. DDT FAQ Study Malaria clock And so on...studies have shown that DDT does NOT have deleterious effects on fish and wildlife. It's very similar to the ALAR scare from the 70's or 80's. Nothing but junk science and politics. The cost is extremely high in terms of dollars and human lives. As for people living in the Ganges river delta or the Saharan subsistence farmers, people will adapt. Crikey, it's not like the oceans will rise 3 foot tomorrow washing away the land, if it happens at all. And yes, at some point, it does become a prioritized issue list. There is only so much money to go around, unless you advocate confiscating additional earnings from people to pay for other's pet projects that may have little real benefit. In the meantime, there are REAL issues that are CURRENT and need to be addressed TODAY. Malaria, HIV/AIDS, poverty, starvation, etc.

117. Cregnebaa 7:08 PM GMT on February 24, 2006
To those who believe in Human induced warming, it is a current problem. Prevention is always better than reaction. Look at the lastest avian flu, and all the media attention it is getting. Yet it has yet to pass from human to human (not looking forward to if it ever does). Governments are stockpiling flu shots in case this does happen. This is prevention. Reducing our impact on the current enviroment is also prevention and so is current. Member Since: October 19, 2005 Posts: 6 Comments: 322

118. jeffB 9:08 PM GMT on February 24, 2006
Um, F5, Inyo, isn't a discussion of DDT's effects (and related controversies) getting a bit off-topic, if not political? :-) Member Since: July 8, 2005 Posts: 0 Comments: 40

119. Inyo 3:48 AM GMT on February 25, 2006
um, i am a biologist and i can guarantee that ddt has been proven to weaken the shells of eggs and inhibit them from surviving. Sure, 'who cares about birds' etc, but if you douse the world with ddt, mosquitos WILL eventually develop immunity, and birds, one of their only natural predators, will crash in population. the links you posted are just to political rants and are not scientifically impartial results. I could point you to many, many papers documenting the effect of DDT on a lot of birds off the coast of California, but since this thread is 2 layers deep now, i won't. But seriously.. look at the links you sent me and tell me they arent horribly biased. The best way, in my opinion, to treat malaria, is to develop better vaccines and treatments for the disease itself. Trying to eliminate mosquitos is a lost cause.. i wish it could be done too! also, on a side note, global warming has been shown to allow malaria-carrying mosquitos to move north in their range. So the issues are not unrelated. Member Since: September 3, 2002 Posts: 42 Comments: 765

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