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Member (Idle past 5849 days) Posts: 7405 From: satellite of love Joined: |
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Author | Topic: Global Warming... fact, fiction, or a little of both? | |||||||||||||||||||
gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: I wouldn't say that it's "absurd". Pretty much the only time you have a polar continent that's covered in an icecap is during an Ice Age, or in our case, an interglacial. Because you need a conveniently positioned continent as well as a favorable climate to accomplish this, ice ages are fairly rare in Earth's history, and by definition this is when you have a have a continental ice cap. In fact, I wouldn't say that we aren't in an Ice Age now, just not in a glaciation.
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: The part about our changing our behavior is an inherently political question. The science itself is independant of whether or not we can, will, or should sign treaties to reduce emissions. That kind of question is primarily for diplomats, economists, and partisan politicians to calculate.
quote: Well, we know that we're releasing CO2 and a half dozen or so other greenhouse gases into the atmosphere. We know that the ground reradiates heat as thermal infrared, and we know that GHGs absorb and reradiate that. Some component of that reradiated energy must be directed back at the ground unless there are some very bizarre physics going on up there that nobody has yet to discover. Not suprisingly, we know that the average global temperature is rising (BTW, Crichton apparently misunderstood the meaning of 'average global temperature' in his book, since his characters apparently travel to a station that shows a local trend of cooling.) So we can arrive at a hypothesis that our GHGs are causing a warming, and we can construct models that generate testable results. For a long time, it was pretty easy to doubt global warming because soundings and satellite temperature measurements contradicted the ground data. But in the last year or so, it was discovered that the satellite data was being cluttered by gradual orbit decay and that some of the diurnal signal they were getting was actually from nightime surfaces. For example, see Vinnikov and Grody, Global Warming Trend of Mean Tropospheric Temperature Observed by Satellites, Science, Vol 302, Issue 5643, 269-272, 10 October 2003 and a few similar papers in the same journal in recent years. Here's a good article posted on the 'net by one of the scientists involved: RealClimate: Et Tu LT? Further, there's a warming trend in the global ocean from 1948-1998 as measured at a depth of 3000 meters. Since the ocean has a lot of thermal inertia, this is pretty clear evidence that this is a true, global trend and not noise in the data. (Levitus et. al., Warming of the World Ocean, Science, Vol 287, Issue 5461, 2225-2229 , 24 March 2000) And the discrepancy in balloon-borne measurements just bit the dust as well: Sherwood, Lanzante, Meyer. Radiosonde Daytime Biases and Late-20th Century Warming, Science, Vol 309, Issue 5740, 1556-1559, 2 September 2005. From the abstract:
quote: Now we have arrived at a point where the surface observations, ocean temperatures, radiosonde data, and satellite measurements are consistent with model predictions. That doesn't "prove" global warming and further testing and refinement of these models will continue as understanding of the climate and additional measurements accumulate. However, as of now the theory of anthropogenic global warming is perfectly good science. I know that bald links are discouraged, but I think these can add additional information for this debate to anyone interested. I think they are tangential to the debate but they cover topics that have been raised. This shows how closely models can approximate climate: RealClimate: Planetary energy imbalance? Here's an article on the myth that was already mentioned in this thread that scientists once believed humans would cause an ice age and that it somehow has a bearing on GW today: RealClimate: The global cooling myth An article entitled "Michael Crichton's 'State of Confusion'" RealClimate: Michael Crichton’s State of Confusion Another installment from RealClimate, "Michael Crichton’s State of Confusion II: Return of the Science" RealClimate: Michael Crichton’s State of Confusion II: Return of the Science
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: Statistical analyses have shown that hurricane frequency is definately up in recent years. But there are multidecadal cycles in frequency that can also account for this. I'm not ready to pin on it global warming yet, but some papers have come out recently that now say that a warming could cause more, and more intense, hurricanes. They've also found a more convenient way to measure hurricane incidence and intensity by calculating the average heat dissipated by hurricanes instead of merely intensity or numbers. (If this trend of linking GW to hurricanes continues, it is a new development. Dr. Christopher Landsea resigned from the IPCC not too long ago because he thought that his superior was playing up last year's season as a result of global warming when the consensus at the time was that GW would not significantly increase hurricane incidence or intensity through 2070).
quote: That is exceedingly unusual, but I don't know that a direct warming of the atmosphere would cause it. I understand that the reason the tropics don't get hail is because the freezing line is so high up that it's hard to make hail in the first place and most of it melts or sublimates on the way down. If you are getting hail now, my first guess would be that the freezing line might have come down a bit, which would mean it was a little cooler aloft. Of course, climate is complex and predicting the consequences of warming for a particular place is very difficult to do. And it's also hard to try to construct a global trend from anomalous weather in a single locality.
quote: Please do that if you can. That would be a thing to see... While we're talking about weather oddities, Brazil got hit by its first recorded hurricane this season. This message has been edited by gene90, 09-14-2005 06:05 PM
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: That would be a self-regulating system, not the onset of a cooling trend. It would stay around an equilibrium.
quote: Here's an interesting summary of a Perspectives column written in Science:
quote: Science, Vol 304, Issue 5669, 400-402 , 16 April 2004 This message has been edited by gene90, 09-15-2005 10:00 AM
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: Well, as I understand it ice has been historically rare on Earth outside of Ice Ages. Even now when we have midlatitude glaciers (for the moment) climate is still a bit colder than normal. There *might* have been some glacioeustacy in the Cretaceous, a paper like that was presented at GSA, I think last year. And that was definately a greenhouse climate. But as more of a general rule of thumb than an absolute statement of fact, and assuming we are talking about ice that persists yearlong, I would agree with jar. This message has been edited by gene90, 09-15-2005 10:05 AM
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: I tend to agree with that.
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: Then maybe you will find this statement better: as a general rule of thumb across Earth history, the odds are against you finding permanent land ice unless you are in an Ice Age. That is because: (a) Today's climate is unusually cool. (b) It is unusual for there to be land masses near the poles. I do not mean that if I open my freezer and find ice there, I am in an Ice Age, although it could be argued that in that case it would technically be true. You might be find be able to find permanent land ice on Earth during non-Ice Ages if you scoured the planet. However, because the key definition seems to be "wherever jar happens to be at the time", and if jar has a random geographical occurence, then yes, the rule of thumb will usually hold true.
quote: Hence the need to divide the rather colloquial term "Ice Age" into glacials and interglacials. Human civilization is an artifact of our current interglacial. Alpine glaciers have occasionally devoured European villages but there aren't continental glaciers on North America or Europe like there were during previous glacials.
quote: Obviously the quantity definition is superior. About the only reason I have sought to defend the existance of ice definition is because I think it has some validity, in that land ice (notice I'm further qualifying it) is usually rare. Of course, this is now a non-issue because you have acknowledged this already.
quote: No, I'm thinking of it as a 'rule of thumb'. As a definition, in the context you seek to use it, it is clearly inferior.
quote: Technically that's true, but we're arguing semantics. There is a significant practical distinction to be made between the interglacial we live in and when glaciers eat Manhattan. This message has been edited by gene90, 09-15-2005 11:02 AM
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: It would probably take much longer than 100 years to produce significant continental glaciers even if it started tomorrow. Also, the idea of GW ever causing an Ice Age doesn't seem to be a consensus view, since Science seems to have recently ran a refutation of it in their "Perspectives" column. I posted the summary in this thread. It'll be a little while longer till we all get free online access to the compete article. This message has been edited by gene90, 09-15-2005 11:31 AM
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: Naturally it's increasing faster than anything that could compensate for it, that's why the CO2 concentration has a positive slope. Though there's some science now that does imply a 'lag' in the warming of the oceans.
quote: A little, but more to the point heat has to increase, be it sensible (like you can measure with a thermometer) or latent. As has been said, really "climate change" is a better term than "global warming" for weasal purposes--because it is less specific...and if negative feedback loops conspire to not allow such a great increase in average temperature, climate still has to change to keep that temperature in check . This message has been edited by gene90, 09-15-2005 12:41 PM
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: I haven't read it, and should have said so explicitly.
quote: Looking at: Global Warming Trend of Mean Tropospheric Temperature Observed by Satellites by Vinikov and Grody, Science, Vol 302, Issue 5643, 269-272, 10 October 2003. In the abstract they say:
quote: So they are using the entire dataset accumulated by a number of satellites over many years. There are other groups working on the contradictions between models and even between satellite datasets. For example: Santer et. al., Influence of Satellite Data Uncertainties on the Detection of Externally Forced Climate Change. Abstract:
quote: I think this segment from the body of the paper should do a fair job of showing the problem:
quote: So the situation is really more complicated than merely saying that satellite data either consistent or inconsistent with a global warming. It looks like the first group to reduce the data found no warming, but others using different instruments found a warming consistent with the models and with the observed surface trend. I'm not a climatologist, statistician, or physicist so I can't claim to really understand everything in that paper. But the parts I do understand seem pretty clear, that reducing data in different ways generates different results. I suspect some circularity in there since they "simulated" MSU temperatures with a model and then compared it data from channels T2 and T4, but you still have the old fashioned thermometers on the surface that, simply put, agree with one dataset and contradict another. I tend to side with the RSS based on this.
quote: I don't know the answer offhand, but it seems likely that there are many other effects influencing climate. For example, the little cold spell around 1991--probably causd by the eruption of Mt. Pinatubo. Superimposed on that and the anthropogenic GHG component you have reductions in sulfate emission which could contribute to warming as well as other air pollution controls and you have a run up to around 2000 where Sun becomes more active (I have not checked to see if this cycle caused appreciable changes the radiation budget, but it is my understanding that increased sunspots are associated with slight increases in the solar constant). But I would count on there being other natural factors that for a few decades will enhance or detract from the warming attributed to GHGs. The real strength seems to not be that GHGs are the strongest climate driver, but the most persistant. Volcanic aerosols can cause a cooling but they don't seem to last very long. Actually separating out these factors is probably something that can only be done in the models. The good news is that you can measure temperature and aerosols and GHG concentrations, and testable predictions from the models. I am optimistic that while Earth sciences aren't quite as easy to reduce to the laboratory as chemistry or some of the other, 'harder' fields, it's good science and climate models aren't an exception.
quote: This is a very important point to make. Correlation is not proof of causality. GHGs may cause climate change but climate change probably affects the atmospheric concentration of GHGs. For example, imagine solar output goes up and warms the climate. That could thaw millions of square kilometers of permafrost and that would create a significant increase in atmospheric CO2. So, yes, that's a piece that may never quite fall into place simply from graphing the two, even though physics does strongly imply that GHGs "should" be absorbing and reradiating outgoing heat back to Earth.
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: That's technically true, but in meteorology sensible heat is thermal, the term "latent heat" means the energy in a body of air, ie, the heat you could release through condensation. But yeah, you're right about the part that it's an energy increase, and my wording could offend people that know a lot more about thermodynamics.
quote: All emphasis is original. Can't get much more explicit than that. That's from a freshman Introduction to Meteorology textbook, Meteorology Today, Fifth Edition, by C. Donald Ahrens, West Publishing Company, page 33.
quote: Your jargon is different from mine. I should have specified "latent heat" rather than "heat" in that sentence but we're on the same page regarding the actual process. This message has been edited by gene90, 09-15-2005 10:49 PM
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: I don't see a lot of relevance to what I said and the actual point is eluding me but you might be interested in my previous reference in this thread to the warming of the oceans and also a Hansen paper in the June 2005 about a 'lag' in the warming of the system.
quote: This message has been edited by gene90, 09-16-2005 06:37 PM
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: I have no interest in discussing what I said when the meaning is clear. This message has been edited by gene90, 09-16-2005 07:36 PM
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
I noticed that Holmes quoted Dr. Landsea (an easily remembered name) on hurricanes, global warming, and that political debate that's ever present in the background. Landsea quit the IPCC last January because of what he viewed as distortion of his specialty (hurricanes and global warming) for political purposes.
Letter of explanation:’ Quote:Intergovernmental Panel on Climate Change - Wikipedia Yeah, I understand that now there are two recent papers that could turn the climate community around, we'll wait and see. But even if it does, I think this is interesting from a political standpoint.
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gene90 Member (Idle past 3852 days) Posts: 1610 Joined: |
quote: I don't that's considered a very credible position.
quote:
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