Over the past week or so, I've noticed a number of articles and posts about the Arctic. There seems to be some kind of ongoing flap about some climate change deniers denying that the extreme north is warming. I have (mostly) avoided reading those original posts because they can't be a good use of time (one example will essentially prove my point). Following each denier rant seems to be a barrage of posts refuting their claims. The good things about these posts are that they more carefully present evidence to support themselves and the reader can actually learn something from them (here's a good example from Tamino). Unfortunately, I don't think these posts help to convince the public of the state of the science, since the public doesn't read them (sorry, but they don't). If a person is willing to dig into the climate change issues enough to read these posts, I think they have already decided what they believe before they get involved (even passively) in these "debates." (They are, of course, not debates at all.)
Another article from the NYTimes.com helps explain why the warming Arctic is an important issue, not just for climate research, but for geopolitical and economic reasons. A commercial ship is about to finish traversing the Northeast Passage from South Korea to the Netherlands. This cuts thousands of miles off the usual trip. If more ships start going this way during the summer, Russia stands to profit because the ships will sail through Russian waters. The path has historically been blocked by ice even in the summer, but as the Arctic has warmed, summer ice has become reduced in area and thickness, and over the past few years the Northeast Passage has been open for a few weeks each year. Similarly the Northwest Passage through Canada's many islands has been open, but so far commercial ships haven't used it yet (they will soon, I would wager). These are impacts of climate change, and unlike most other impacts, these ones could be interpreted as positive for some of the involved parties. Of course, along with these routes opening, the open waters spell doom for the polar bears who have become unwitting symbols of the ecological impacts of a warming world.
On the research side of things, the warming Arctic has long been considered the proverbial canary in the coal mine. Because of strong positive feedbacks associated with snow and ice retreat and atmospheric water vapor, there has emerged a general understanding of the polar regions (especially in the north) as being particularly sensitive. The poles are expected to warm most rapidly, an effect usually called "polar amplification." There is some scientific uncertainty about whether the amplification is observed yet (e.g., this RealClimate post from C. Bitz), but there is strong consensus among researchers that it will emerge from the noise. This view is supported by climate modeling experiments, in which all the reliable models predict an amplified response in the Arctic. From my reading, which is incomplete, this extends to the Antarctic, but only on slightly longer timescales because of the heat transfer into the Souther Ocean.
Showing posts with label Arctic. Show all posts
Showing posts with label Arctic. Show all posts
2009-09-11
2007-09-11
The Arctic and its role in the climate change discourse
I spend most of my time thinking about clouds in the tropics and subtropics, but lately there's been a lot of mainstream coverage of the Arctic and how it relates to climate chage. I've posted about Arctic issues before, of course, but today I not only want to highlight a little of the coverage that I've noticed lately, but also warn you, gentle reader, that this is really just going to be one of myriad posts, articles, stories, and sundry coverage of the Arctic over the coming 2-3 years (and probably beyond). Why? Because of the "International Polar Year," which is a big enough deal to have its own domain: ipy.org. It is, as the name implies, an international effort to better understand the Earth system near the poles, from their web site:
Don't fool yourself either, this is not a group of environmental activists who are out trying prove something; this is a concentrated period of study of the Arctic and Antarctic by the people who do that work anyway. It should lead to some great collaborations and synthesis of datasets that haven't been able to be compared or incorporated in meaningful ways before.
So that is the future, what is going on now?
Well, just over the past few days I've read a few interesting tidbits about the Arctic, which people seem to enjoy discussing more than the Antarctic (but more on that later). One of the poster children for climate change awareness is the polar bear, which relies on big pieces of sea-ice floating around near other pieces of sea-ice. The bears hang out on the ice, get hungry, dive in after fish or seals, and come up onto more ice. Apparently they aren't so well adapted to feeding on land, plus there isn't as much food available on land for them. Anyway, a quick article from the BBC, which came to be via ClimateArk, reports on a study that suggests two-thirds (2/3) of the polar bear population will be gone by the middle of the century [LINK]. That's 30-50 years from now, if you're keeping score at home. Why are the bears going to disappear? Because the ice is going away. So what does that mean for a species that relies on ice rafts as hunting platforms? It means that the bears are going to starve and drown. That is a fact. There is already evidence that some populations of polar bears are losing weight, and it probably isn't in preparation for beach season (Regehr et al 2006, also Roberson 2005 (news), Obbard et al. 2006).
This leads directly into our topic number two: sea-ice. This is one of the reasons it's more interesting to talk about the Arctic than the Antarctic, actually. Think about the globe, and picture the poles; the south pole is covered by a landmass (Antarctica) which is actually pretty large, extending far from the pole before giving way to the Southern Ocean. The fact that it is land, combined with the fact that it is surrounded by a continuous ring of ocean, makes climate change near the pole more difficult to understand: the ice in the middle of Antarctica isn't melting. And the sea-ice is much more seasonal (for the most part, though don't forget the Larson B ice shelf!) than in the Arctic (we're painting with a broad brush here). The Arctic is just an ocean, really, which provides easy passage among North America, Europe, and Asia, you remember the Northwest Passage [news], except that it has historically been blocked up by sea-ice. Lately this isn't so true [news, Randy Boswell].
The opening of the Northwest Passage is due to summertime melting of sea-ice, as discussed in Randy Boswell's very nice piece above. There has always been a lot of seasonal sea-ice around the Arctic. During the winter there is little to no sunshine available to deliver energy to warm the surface or melt ice, so as temperatures drop, ice forms, and it stays there until summer when the sun comes out. So that happens every year, and is perfectly normal and expected. However, what has happened over the past few years is a tremendous summertime melting, and just about every year now we hear about how sea-ice extent and sea-ice area are reaching record lows. One of the problems with this is that there is a potential feedback, since the "permanent" sea-ice (that ice that does not melt during the summer) is being reduced each year, so during the winter the ice that grows is thin, leading to quick melting in the summer, which exposes more permanent sea-ice to warm water and sunshine, leading to more loss and a diminished base amount of ice going into the winter. This most recent report suggests that the speed of this cycle might have been underestimated, and now some experts (yes, they are experts in Arctic sea-ice) say that an ice-free Arctic (in the late summer) could exist by 2030 (Serreze et al 2007a,b), which is right around the corner. This bodes ill for the polar bears.
Finally on this subject, it is interesting to note the relationship between the absurd observed sea-ice melt in the last few years compared with our best comprehensive climate models (Serreze et al. 2007b, Overland & Wang 2007). Some of the current-generation models do sort of okay, while basically all of them show a strong trend in the Arctic, but none of the models accurately predict the magnitude of the observed trend. Let me reiterate that these models don't know anything about the observations; they are physical models of climate system forced by atmospheric composition (carbon dioxide) and sunshine, so this isn't a matter of poor data assimilation or statistical techniques or a poor model (in the sense of statistical modeling). This is a dramatic underestimation of the impact of climate change on a region of the world known to be prone to positive feedbacks. What this means is that our "uncertainty" about the future of climate change goes in both directions. Climate change deniers like to point out problems with the models that they think lead to unlikely warming, but here we have a beautiful example of the models underestimating what is actually happening. Perhaps the models are too conservative? Not really, I just wanted to be provocative for a moment. My interpretation is that we need to improve the physics in the models, and probably spend more effort in doing atmosphere-ocean-ice interactions much better than this round of climate models. That is a rant I'll save for later though, as this post is stretching the average blog reader's patience.
Some references:
Regehr, E.V., Amstrup, S.C., and Stirling, Ian, 2006, Polar bear population status in the southern Beaufort Sea: U.S.
Geological Survey Open-File Report 2006-1337, 20 p. [PDF]
Obbard, Martyn E., Marc R.L. Cattet, Tim Moody, Lyle R. Walton, Derek Potter, Jeremy Inglis, and Christopher Chenier, 2006, Temporal Trends in the Body Condition of
Southern Hudson Bay Polar Bears. Climate Change Research Information Note, Issue 3. Ministry of Natural Resources, Ontario, Canada, 8 p. [PDF, see also MNR SIT]
Serreze, M. C., M. M. Holland, and J. Stroeve. 2007. Perspectives on the Arctic's shrinking sea-ice cover. Science 315(5818): 1533-1536, doi:10.1126/science.1139426. [pdf]
Stroeve, J., M. M. Holland, W. Meier, T. Scambos, and M. Serreze. 2007. Arctic sea ice decline: Faster than forecast. Geophysical Research Letters 34, L09501, doi:10.1029/2007GL029703.
Overland, J. E., and M. Wang (2007), Future regional Arctic sea ice declines, Geophys. Res. Lett., 34, L17705, doi:10.1029/2007GL030808. [pdf]
IPY, organized through the International Council for Science (ICSU) and the World Meteorological Organization (WMO), is actually the fourth polar year, following those in 1882-3, 1932-3, and 1957-8. In order to have full and equal coverage of both the Arctic and the Antarctic, IPY 2007-8 covers two full annual cycles from March 2007 to March 2009 and will involve over 200 projects, with thousands of scientists from over 60 nations examining a wide range of physical, biological and social research topics. It is also an unprecedented opportunity to demonstrate, follow, and get involved with, cutting edge science in real-time.
Don't fool yourself either, this is not a group of environmental activists who are out trying prove something; this is a concentrated period of study of the Arctic and Antarctic by the people who do that work anyway. It should lead to some great collaborations and synthesis of datasets that haven't been able to be compared or incorporated in meaningful ways before.
So that is the future, what is going on now?
Well, just over the past few days I've read a few interesting tidbits about the Arctic, which people seem to enjoy discussing more than the Antarctic (but more on that later). One of the poster children for climate change awareness is the polar bear, which relies on big pieces of sea-ice floating around near other pieces of sea-ice. The bears hang out on the ice, get hungry, dive in after fish or seals, and come up onto more ice. Apparently they aren't so well adapted to feeding on land, plus there isn't as much food available on land for them. Anyway, a quick article from the BBC, which came to be via ClimateArk, reports on a study that suggests two-thirds (2/3) of the polar bear population will be gone by the middle of the century [LINK]. That's 30-50 years from now, if you're keeping score at home. Why are the bears going to disappear? Because the ice is going away. So what does that mean for a species that relies on ice rafts as hunting platforms? It means that the bears are going to starve and drown. That is a fact. There is already evidence that some populations of polar bears are losing weight, and it probably isn't in preparation for beach season (Regehr et al 2006, also Roberson 2005 (news), Obbard et al. 2006).
This leads directly into our topic number two: sea-ice. This is one of the reasons it's more interesting to talk about the Arctic than the Antarctic, actually. Think about the globe, and picture the poles; the south pole is covered by a landmass (Antarctica) which is actually pretty large, extending far from the pole before giving way to the Southern Ocean. The fact that it is land, combined with the fact that it is surrounded by a continuous ring of ocean, makes climate change near the pole more difficult to understand: the ice in the middle of Antarctica isn't melting. And the sea-ice is much more seasonal (for the most part, though don't forget the Larson B ice shelf!) than in the Arctic (we're painting with a broad brush here). The Arctic is just an ocean, really, which provides easy passage among North America, Europe, and Asia, you remember the Northwest Passage [news], except that it has historically been blocked up by sea-ice. Lately this isn't so true [news, Randy Boswell].
The opening of the Northwest Passage is due to summertime melting of sea-ice, as discussed in Randy Boswell's very nice piece above. There has always been a lot of seasonal sea-ice around the Arctic. During the winter there is little to no sunshine available to deliver energy to warm the surface or melt ice, so as temperatures drop, ice forms, and it stays there until summer when the sun comes out. So that happens every year, and is perfectly normal and expected. However, what has happened over the past few years is a tremendous summertime melting, and just about every year now we hear about how sea-ice extent and sea-ice area are reaching record lows. One of the problems with this is that there is a potential feedback, since the "permanent" sea-ice (that ice that does not melt during the summer) is being reduced each year, so during the winter the ice that grows is thin, leading to quick melting in the summer, which exposes more permanent sea-ice to warm water and sunshine, leading to more loss and a diminished base amount of ice going into the winter. This most recent report suggests that the speed of this cycle might have been underestimated, and now some experts (yes, they are experts in Arctic sea-ice) say that an ice-free Arctic (in the late summer) could exist by 2030 (Serreze et al 2007a,b), which is right around the corner. This bodes ill for the polar bears.
Finally on this subject, it is interesting to note the relationship between the absurd observed sea-ice melt in the last few years compared with our best comprehensive climate models (Serreze et al. 2007b, Overland & Wang 2007). Some of the current-generation models do sort of okay, while basically all of them show a strong trend in the Arctic, but none of the models accurately predict the magnitude of the observed trend. Let me reiterate that these models don't know anything about the observations; they are physical models of climate system forced by atmospheric composition (carbon dioxide) and sunshine, so this isn't a matter of poor data assimilation or statistical techniques or a poor model (in the sense of statistical modeling). This is a dramatic underestimation of the impact of climate change on a region of the world known to be prone to positive feedbacks. What this means is that our "uncertainty" about the future of climate change goes in both directions. Climate change deniers like to point out problems with the models that they think lead to unlikely warming, but here we have a beautiful example of the models underestimating what is actually happening. Perhaps the models are too conservative? Not really, I just wanted to be provocative for a moment. My interpretation is that we need to improve the physics in the models, and probably spend more effort in doing atmosphere-ocean-ice interactions much better than this round of climate models. That is a rant I'll save for later though, as this post is stretching the average blog reader's patience.
Some references:
Regehr, E.V., Amstrup, S.C., and Stirling, Ian, 2006, Polar bear population status in the southern Beaufort Sea: U.S.
Geological Survey Open-File Report 2006-1337, 20 p. [PDF]
Obbard, Martyn E., Marc R.L. Cattet, Tim Moody, Lyle R. Walton, Derek Potter, Jeremy Inglis, and Christopher Chenier, 2006, Temporal Trends in the Body Condition of
Southern Hudson Bay Polar Bears. Climate Change Research Information Note, Issue 3. Ministry of Natural Resources, Ontario, Canada, 8 p. [PDF, see also MNR SIT]
Serreze, M. C., M. M. Holland, and J. Stroeve. 2007. Perspectives on the Arctic's shrinking sea-ice cover. Science 315(5818): 1533-1536, doi:10.1126/science.1139426. [pdf]
Stroeve, J., M. M. Holland, W. Meier, T. Scambos, and M. Serreze. 2007. Arctic sea ice decline: Faster than forecast. Geophysical Research Letters 34, L09501, doi:10.1029/2007GL029703.
Overland, J. E., and M. Wang (2007), Future regional Arctic sea ice declines, Geophys. Res. Lett., 34, L17705, doi:10.1029/2007GL030808. [pdf]
2006-12-12
meltdown
I don't have time to really think too hard about this story, but it is making the rounds, so I'll at least acknowledge it. Some NCAR simulations now predict essentially no late-summer ice in the Arctic by 2040. See the story at BBC [LINK] or at Nature [LINK]. The actual paper is in Geophysical Research Letters [doi:10.1029/2006GL028024].
What does this mean? Well, I haven't had a chance to look closely at the paper, but I have some first impressions. I did get a sneak-peek of these results this summer, and at the same time was introduced to some of the details of the sea-ice model used in CCSM (NCAR's climate model), so maybe I'll be able to say something halfway meaningful. The paper itself does not predict an ice-free Arctic in 2040, so let's just get that out of the way. This paper is really about the possibility of abrupt decreases in sea-ice in a changing climate, and the current generation of climate models suggest a real possibility of large reductions in perennial ice coverage in the first half of the 21st century. The main focus is a set of CCSM simulations using one of the emissions scenarios from IPCC. They also take a look at some of the results from other IPCC models. The CCSM always has what the authors call "abrupt reductions" in Arctic ice, and several of the other models also show large reductions.
I am willing to accept these results, but I think some skepticism has to be exercised still. First off, this is a GRL paper, which is a journal of short, usually preliminary, work focusing on "sexy" results. The peer-review process for GRL is sometimes thought to be a little lax, and sometimes the quality of the work is questionable. That does not seem to be an issue for this paper; the CCSM is a respected climate model, the authors are top-notch climate scientists, and this work is presented well. That said, this is not the last word on this project; I'm sure that the authors are doing more detailed work and are planning a longer, more careful analysis for another journal (e.g., Journal of Climate, Climate Dynamics). The best thing that could do would be to better quantify what "abrupt changes" really are, and the physical processes that trigger them, which is a big open question in this paper. They say the abrupt changes are driven by thermodynamics, but don't really present evidence of this; I assume they mean that wind patterns/ocean currents are changing to just move ice out of the Arctic, but it is not explained. The other thing to keep in mind is that even in the current generation climate models, the sea-ice models are fairly crude. I don't mean that in a bad way, the people working on these models are doing the best they can. Ice processes are quite complicated, and to properly model sea-ice, much like "properly" modeling clouds, the simulations need to be run in much higher resolutions. That kind of resolution is too expensive right now, and even if the resources were there, it would be a tough sell to dedicate it to the sea-ice component rather than better atmospheric and oceanic components. This particular climate model is known to be fairly sensitive, and when it gets knocked out of equilibrium, the sea-ice is one of the things known to respond fairly erradically. So while I think the CCSM, and several other high-end climate models, can get a lot of important changes correct, we still can't trust the details of these fully coupled simulations. My interpretation is then something like this: in the near future (50 years), it is likely that rapid reductions in perennial Arctic sea-ice will be observed, associated with (but not well-correlated with) increasing atmospheric greenhouse gases.
What does this mean? Well, I haven't had a chance to look closely at the paper, but I have some first impressions. I did get a sneak-peek of these results this summer, and at the same time was introduced to some of the details of the sea-ice model used in CCSM (NCAR's climate model), so maybe I'll be able to say something halfway meaningful. The paper itself does not predict an ice-free Arctic in 2040, so let's just get that out of the way. This paper is really about the possibility of abrupt decreases in sea-ice in a changing climate, and the current generation of climate models suggest a real possibility of large reductions in perennial ice coverage in the first half of the 21st century. The main focus is a set of CCSM simulations using one of the emissions scenarios from IPCC. They also take a look at some of the results from other IPCC models. The CCSM always has what the authors call "abrupt reductions" in Arctic ice, and several of the other models also show large reductions.
I am willing to accept these results, but I think some skepticism has to be exercised still. First off, this is a GRL paper, which is a journal of short, usually preliminary, work focusing on "sexy" results. The peer-review process for GRL is sometimes thought to be a little lax, and sometimes the quality of the work is questionable. That does not seem to be an issue for this paper; the CCSM is a respected climate model, the authors are top-notch climate scientists, and this work is presented well. That said, this is not the last word on this project; I'm sure that the authors are doing more detailed work and are planning a longer, more careful analysis for another journal (e.g., Journal of Climate, Climate Dynamics). The best thing that could do would be to better quantify what "abrupt changes" really are, and the physical processes that trigger them, which is a big open question in this paper. They say the abrupt changes are driven by thermodynamics, but don't really present evidence of this; I assume they mean that wind patterns/ocean currents are changing to just move ice out of the Arctic, but it is not explained. The other thing to keep in mind is that even in the current generation climate models, the sea-ice models are fairly crude. I don't mean that in a bad way, the people working on these models are doing the best they can. Ice processes are quite complicated, and to properly model sea-ice, much like "properly" modeling clouds, the simulations need to be run in much higher resolutions. That kind of resolution is too expensive right now, and even if the resources were there, it would be a tough sell to dedicate it to the sea-ice component rather than better atmospheric and oceanic components. This particular climate model is known to be fairly sensitive, and when it gets knocked out of equilibrium, the sea-ice is one of the things known to respond fairly erradically. So while I think the CCSM, and several other high-end climate models, can get a lot of important changes correct, we still can't trust the details of these fully coupled simulations. My interpretation is then something like this: in the near future (50 years), it is likely that rapid reductions in perennial Arctic sea-ice will be observed, associated with (but not well-correlated with) increasing atmospheric greenhouse gases.
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