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Ice mass the size of Greenland overlooked in climate models
- yread 13y ago> The highly accurate dating and long time span of those fossils have allowed scientists to estimate fluctuations in sea level, and thus ice content, by extrapolating from variations in the ratio of oxygen isotopes How do they estimate sea level from the ratio of oxygen isotopes? I've found just this http://en.wikipedia.org/wiki/Δ18O http://en.wikipedia.org/wiki/Δ18O but it talks only about temperature, salinity and amount of evaporation
- ovis 13y agoLighter isotopes preferentially get deposited on and form the ice sheets, so increases in ocean d18O correlate with glaciations.
- kaybe 13y agoThe Rayleigh process describes the continous depletion of a reservoir through a fractionationing process - evaporation. It comes from the fact that heavier isotopes need slightly more energy for a phase change and thus get enriched in the fluid phase. In the case of water, it is mainly the stable O18 (as opposed to the abundant O16). - Lighter isotopes evaporate easier and precipitate down on land. If they don't return to the ocean for a long time due to freezing and glaciation, the ocean has a higher ratio of heavy to light isotopes. More ice means lower ocean level, and since the ratio in the ocean is dependent on the missing water mass, calculations directly give the sea level. Now how do we know what the isotope ratio was in the past? In the oceans, there are those small animals (foraminifera) that build the oxigen from water into their shells. The Wikipedia article you found discusses this. (Another fractionation process, add more calculations here. Additional temperature dependance.) When they die, they float to the ocean floor and, in time, form sediments and eventually lime rock, which can be drilled for probes. Furthermore, different kinds live in different depths, giving us even more information. This can be used for the past 70 million years, since that's the age of the oldest ocean floors. Almost (!) everything older has been subducted again. However, it is not easy to disentangle the temperature effect from the ice volume effect. You can check those out, if you're interested, they explain more thoroughly than the wikipedia article: shorter lecture script: http://www.iup.uni-heidelberg.de/institut/studium/lehre/AquaPhys/docMVEnv3_13/AqSysSkript_part2_chap1.pdf http://www.iup.uni-heidelberg.de/institut/studium/lehre/Aqua... long looooong version (read this and become a hydroscientist long): http://www-naweb.iaea.org/napc/ih/IHS_resources_publication_hydroCycle_en.html http://www-naweb.iaea.org/napc/ih/IHS_resources_publication_...
- yread 13y agoThanks for this comprehensive response (I didn't expect any less from HN ;) I understood the part about O18 ending up less in the glaciers but I couldn't really grasp that if the water is in glaciers it isn't in the sea. I also thought it would be impossible to get rid of influence of the temperature (gradient with depth, latitude, ocean currents, ...) but it's probably not impossible, just difficult. Also for anybody who doesn't click in the "loooooong" version has 6 volumes...
- brittohalloran 13y agoTLDR; Since the historical ice models, driven by fossil based sea level readings in Barbados, failed to account for the way the Earth's crust bends under the weight of a massive ice sheet on top of it, there was actually much more ice than previously thought. The exact implications aren't given, but it is implied that global warming is worse than we thought (has melted more ice).
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- tezza 13y agoNot sure I get the same conclusion you do from the same article. Worse than we thought?: "It allows for the possibility that there is significant melting of the East Antarctic Ice Sheet," Rowley said. "Or it allows for a simple interpretation of no melting." There is a simple interpretation of no melting. Also, previously in the article they show that the models used to predict melting are suspect. The historical link of 'melt' being caused by CO2, may in fact be flattening caused by crust flexing.
- Retric 13y agoThe crust flexes in response to freasing or melting but it don't not significantly buldge without reason.
- philhippus 13y agoWith that sentence you are either a rather prodigious 6 year old or a grammatically challenged adult.
- tome 13y agoOr a non-native English speaker?
- rjknight 13y agoThe big melt was the end of the last ice age. That's far larger than anything that has yet happened due to climate change, so they're not really talking about ice that has been melted by global warming in the sense of post-industrial climate change. However I think your basic assumption is right - this evidence would seem to suggest that, for a given amount of warming, we get more ice melt than we previously assumed.
- LatvjuAvs 13y agoDat global warming, must trow more money at it.
- TausAmmer 13y agoChange happens, all we can do is adopt, for now. Clear coastlines, clean low river banks. If anything, extremes are going to ramp up in count, adopt and build infrastructure around it. Paying gigantic amount of money to members that come together few times a year do not solves anything.
- AutoCorrect 13y agoI already have all the children I can comfortably support, and we plan on ADAPTING ;)
- gizmo686 13y ago>all we can do is adopt, for now. You do realize that we are the first species to be the cause of a mass extinction event. We are also the only species to seriously consider how to terraform another planet [1]. What we need is the environmental movement to stop saying that we are actively destroying the world and the only thing we can do is stop, to one that says we have the ability to control the environment of our own world, and we should do so intelligently. Keep in mind that we are not the first mass extinction event (the Permian–Triassic extinction event killed 96% of all species), but we are the first species to be able to exercise intelligent control over the climate. Also, while the environment will flourish after just like after every other extinction, it won't happen quickly enough for our scientist to be able to study life in the same way that they can with our pre-extintion bio-diversity. [1] http://www.users.globalnet.co.uk/~mfogg/zubrin.htm http://www.users.globalnet.co.uk/~mfogg/zubrin.htm
- zdw 13y agoMost people have a distorted idea of how big Greenland is - it's actually about the size of Saudi Arabia (http://en.wikipedia.org/wiki/List_of_countries_and_dependencies_by_area http://en.wikipedia.org/wiki/List_of_countries_and_dependenc...) and gets distorted by most map projections to outlandish sizes (larger than South America in some).
- lquist 13y agoMost likely a result of the flaws of the Mercator projection (https://en.wikipedia.org/wiki/Mercator_projection#Mathematics_of_the_Mercator_projection https://en.wikipedia.org/wiki/Mercator_projection#Mathematic...).
- yellowbkpk 13y agoSaying it's a result of a flaw in the Mercator projection is like saying zero being undefined is a flaw of the logarithm scale: it's not a flaw, it's a property. If the projection doesn't work for your usecase, don't use it.
- minikites 13y agoOkay, but the Mercator projection is/was used very frequently in schools where there's isn't a choice in the matter. It's such a widespread misconception and most people aren't taught about how map projections work so it's a part of the general public consciousness. https://www.youtube.com/watch?v=n8zBC2dvERM https://www.youtube.com/watch?v=n8zBC2dvERM
- baddox 13y agoNo, I would say that area distortion is a flaw in the Mercator projection. Just because all map projections inevitably have flaws doesn't mean that they're not flaws. If you could have a map projection with no distortions, you would probably use it exclusively.
- b0rsuk 13y agoThe goal of a map is to represent reality and to make it easier to orient yourself. The goal of math is often just math. Eventually, someone finds a way to utilize some esoteric calculations and properties in a field or two. No one is bothered that math is often out of sync with perceivable (in the Common Sense way, at least) world. But Mercator's projection can be misleading. It's not like a metro map - it looks quite natural and people assume it can be taken literally.
- snowwrestler 13y agoI think this headline (which comes from the article) is a bit misleading. The total mass of the overlooked historical ice is about the mass of the Greenland ice sheet, but it was not all in one place like Greenland is. The article says's it's actually about a 10% error in a global historical reconstruction. In addition, when I see the phrase "climate models", I think of the global simulations that scientists use to try to predict the future effect of climate change. This article seems to instead be about an historical reconstruction of a past climate.
- prawks 13y agoI think you're right, this article is concerned with determining how much ice has melted since the last glacial maximum, not how much more will melt.
- lftl 13y agoIn addition, when I see the phrase "climate models", I think of the global simulations that scientists use to try to predict the future effect of climate change. This article seems to instead be about an historical reconstruction of a past climate. But aren't the two extremely tightly coupled? I know nothing of climatology, but it's hard for me to imagine how you would construct a future model that didn't rely massively on our picture of how the Earth reacted historically to different pressures. It would seem to me that adding a rather large chunk of ice, and changing past sea level measurements would have a large effect on the predicted future response of the system.
- snowwrestler 13y agoNot as much as you might think. Models simulate a small range of time centered around the present, and are constructed by combining measurable physical quantities with physics equations. Basically, they attempt to simulate "the truth" starting from first principles. Historical reconstruction is about really advanced ways of observing, estimating, and proxying data. The end product is a story of past climates, not a simulation or prediction. It's sort of like the difference between an evolutionary biologist experimenting on fruit flies, and a paleontologist. You need both to get a complete picture of life, but neither's work depends much on the other. In this case I'd be surprised if there is much impact on near-term climate predictions, because isostatic rebound is really slow at century timescales.
- pmorici 13y agoI don't understand the emphasis on 'global warming' / 'climate change' as a marquee issue to drive action on environmental protection. The science behind it seems complex and because it relies so heavily on modeling leaves significant uncertainty in the mind of any lay person that reads about this stuff. I would think a much better way to promote environmental protection would be from the human health angle. Things like Erin Broncovich, Gas Land, (or whatever the air pollution equivalent is) etc... where there is clear documented proof about how environmental contamination is literally killing people. Seems like those would be more compelling reasons to act than some uncertain doom a century from now.
- eli 13y agoBut they're different issues, right? The actions I would take to ensure my drinking water doesn't give me cancer are often different from those I'd take to prevent rising sea levels.
- pmorici 13y agoSorry those might have been bad examples. It's well documented that air pollution also causes human health issues. I'm saying that might be a better thing to highlight than the fact that that same air pollution might cause the tide to rise some unknown amount at some uncertain date in the future.
- pyre 13y ago- Air pollution causes acid rain. - Nobody likes "smog alert" days in large cities (LA, NYC, Toronto, etc). Everyone agrees that breathing in smog is bad. - Burning coal releases radioactive isotopes into the atmosphere. - Air pollution causes ocean acidification. This has the potential to wipe out entire species / aquatic ecosystems. - Ocean dead zones are bad. Stop producing - Significant amounts of methane come from 'cow farts.' Farming livestock for food makes less sense than farming plants. It takes more farmland to support livestock (e.g. something like 1000 lbs plants to produce 100 lbs of meat). [Not to mention all of the freshwater issues with irrigating all of the extra land used to feed the livestock.] - Deforestation of topic rain forests in Indonesia need to stop because they are destroying Orangutan habitat, causing a possible extinction (except for those in captivity / zoos). - Deforestation of the Amazon to make way for farmland / livestock grazing area needs to stop. It contributes a signification portion of the oxygen that we breath to the atmosphere.
- binderbizingdos 13y agotemperatures of the last 12'000 years: http://en.wikipedia.org/wiki/File:Holocene_Temperature_Variations.png http://en.wikipedia.org/wiki/File:Holocene_Temperature_Varia...
- josephlord 13y agoAt a plain reading this seems worthy science but not that newsworthy. Scientists do more (presumably good) work and adjust estimate of ice last ice-age by 10%, climate models may need minor tweak (direction not stated). Did I miss something?