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Why we should observe an increment on the mean intensity in rainfalls and an increment on mean dry days with global warming?

Emanuele Luzio
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This site by climate scientist Frank Wentz discusses the rainfall possibilities of increased temperatures. Although warmer atmosphere contains more water thereby increasing rainfall, changes in circulation could minimize rainfall.

It's also possible that currently wet areas will get wetter and currently dry areas will get drier.

Michael Luciuk
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    Dear Michael, Wentz only observes what the actual water content is but he doesn't have solid attribution of the changes or justified predictions for the future. After all, this experimenter isn't really qualified to do such things. A higher temperature of course means a higher absolute humidity for the same relative humidity but absolute humidity, and therefore temperature, is irrelevant because rain is sparked when relative humidity reaches 100 percent due to water/pressure/temperature conditions. – Luboš Motl Nov 30 '12 at 15:54
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    All the guesses about changed circulation or increased non-uniformities are pure speculations and/or numerical artifacts of overfitted untested models. None of these claims actually follows from any proper physics analysis of the atmosphere and physics actually implies that the opposite sign is to be expected. Global warming, if any, would reduce all the non-uniformities in precipitation and other things. – Luboš Motl Nov 30 '12 at 15:56
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    Incidentally, the fluctuations are so significant and the record is so short so far that we can't even observationally verify the proposition that the average relative humidity of the atmosphere should be more constant than the absolute humidity - because the former is between 0 and 100 percent while the latter may grow larger because of warming. The 1 deg C warming only represents a few percent change in the ratio of the two humidities but the precision with which the humidity trends may be extracted from the observations has an error that's larger. So no changes like that are obs. seen. – Luboš Motl Nov 30 '12 at 16:29
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    I believe that forecasting climate effects like rainfall is still a work in progress. I'm not inclined to dismiss Dr. Wentz,s views on the subject. – Michael Luciuk Nov 30 '12 at 16:45
  • You may not be inclined but it's still true that you don't have any physical evidence for your claims, e.g. that "it's possible that wet will get wetter" etc. You (and Mr Wentz and dozens of others) just use the uncertainties in order to promote one particular kind of answer that is as unjustified as any other answer (and actually less justifiable than the opposite answer) because you find this answer more convenient, for certain reasons. It's called scientific dishonesty. – Luboš Motl Dec 01 '12 at 11:56
  • It's clear that you feel very strongly that you have the answers to Emanuele's question. I don't think it's "scientific dishonesty" to posit a view by someone like Wentz, who has credentials in the topic. Climate is an area that has too many variables for me personally to have a definitive opinion. – Michael Luciuk Dec 01 '12 at 18:31
  • @LubošMotl: if you look at the historic record (i.e., the difference between today's climate and the ice age), global warming changes climate in radical and unpredictable ways. There is no reason and no evidence that it should reduce the non-uniformities. My prediction: some wet areas will get wetter, some wet areas will get dryer, some dry areas will get wetter, and some dry areas will get dryer. Some of these changes will be very large, and some will be small. Some will improve the lives of the inhabitants, but most will make them worse (on the theory that most change is bad). – Peter Shor Dec 30 '12 at 16:37
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Because the statement isn't true while it is more convenient for the popular idea that there is some climate change to worry about.

In reality, irregularities and extremes in precipitation, temperatures etc. are driven primarily by temperature gradients. Because the cold poles are predicted to warm faster than the warm equatorial areas because of various feedbacks, the pole-equator temperature difference is predicted to drop. If true, this will reduce temperature gradients and make many location-dependent quantities more spatially uniform. A higher temporal uniformity is expected as well.

So if there were (significant) global warming, precipition and other processes would probably get more uniform and less extreme. The frequency of rains that are stronger than a given threshold would drop. However, the relative difference in the intensity of rain etc. would be very small because one or few Celsius degrees is a tiny change of the absolute temperature while the natural noise and fluctuations in quantities describing precipitation are of order 100 percent.

This is a textbook material. I was taught those things mainly by Richard Lindzen but e.g. his textbook on atmospheric physics is recommended:

http://www.amazon.com/Dynamics-Atmospheric-Physics-Richard-Lindzen/dp/0521018218/ref=sr_1_2?ie=UTF8&qid=1354290340&sr=8-2&keywords=Richard+Lindzen

Luboš Motl
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    You should mention that the work by Lindzen is highly controversial. Without such a mention, the claim This is textbook material is misleading, because it implies the exact opposite. For example, tropical cyclones are driven by sea surface temperatures, not by equator-pole gradients. Many models, such as the ones by Trenberth, do show an increase in intensity of precipitation events, and warmer climates do tend to have more intense precipitation. – gerrit Feb 12 '13 at 22:37
  • My statement that it is a "textbook material" means that every competent atmospheric physicist must learn this stuff before he or she may start to do actual serious research. The fact that a bunch of incompetent, corrupt, and ideologically driven pseudoscientists wants to make a fact about physics controversial doesn't change anything about that. What you write is complete nonsense from a physics viewpoint. All motion in the atmosphere and anywhere is always governed by gradients. A higher or lower but constant temperature clearly can't induce any macroscopic circulation. – Luboš Motl Dec 05 '14 at 07:16
  • There will always be a gradient between temperatures at the surface and the upper troposphere. The difference between surface and upper tropospheric temperatures increases if surface temperatures increase. Therefore, said gradients increase. More intense surface heating means more intense convection means more intense (tropical) storms. Your accusations of pretty much the entire field of atmospheric science is unscientific and unconvincing. – gerrit Dec 05 '14 at 16:28
  • No, the gradients don't increase - the vertical gradients are given by the lapse rate. What increases is the height of the tropopause - the thickness of the troposphere. This increase due to "global warming" - CO2 or otherwise - is nearly negligible and the hurricane activity is proportional to a power of the height with a moderate exponent, so any impact of these vertical changes on the hurricane activity is guaranteed to be unobservable. It is you, not me, who is attacking atmospheric physics, starting from its most standard graduate textbooks (and from the 2nd law of thermodynamics). – Luboš Motl Dec 06 '14 at 06:44
  • I mentioned a critical thing here - textbook material of atmospheric physics, namely a commonly used graduate textbook covering all these basic physical processes and written by a famous MIT professor. You attacked it, without a glimpse of rational evidence, and even criticized that I used the word "textbook stuff" for textbook stuff, and you suggested something that every good high school student knows to be impossible - namely the suggestion that the thermal motion of atoms is converted to hurricanes. Energy lost in heat can't be turned into useful motion - 2nd law of thermodynamics! – Luboš Motl Dec 06 '14 at 06:46
  • Sure, the gradient, dT/dy as such, does not increase. But a hotter surface, higher troposphere, larger temperature difference between surface and tropopause, is involved with deeper and more intense convective systems thus higher rainfall intensities. Which one can describe as "more energy in the system". As for the 2nd law of thermodynamics, entropy increases in a closed system. The Earth is not a closed system. – gerrit Dec 09 '14 at 05:05
  • Even if this dependence exists, the surface-to-tropopause temperature difference would change by that 1 °C or 2 °C per century at most – which means from 100 °C to 101 or 102 °C, so by one or two percent. The rainfall intensity or whatever is at most a small-exponent power law, so it would change by a percent or two, too. It is absolutely ludicrous to suggest that this change could be measured in the real world – or that it is even dangerous. – Luboš Motl Dec 09 '14 at 08:42
  • The entropy obviously increases with the temperature but there is nothing wrong about the entropy or absolute temperature higher by a fraction of a percent, and it does not detectably increase the intensity of hurricanes, torrential rains, or anything else. The 2nd law implies that the energy lost in the thermal chaos won't spontaneously be extracted and become useful macroscopic motion such as the wind. All thermal engines etc. require temperature differences, not just high temperatures. If you don't understand this comment, you should immediately return your PhD. – Luboš Motl Dec 09 '14 at 08:44
  • Models do not agree to what degree precipitation patterns will change. It is complicated by possibly changing dynamics in both the oceans and the atmosphere. I don't know how you reached the 1° or 2° per century figure. Even a small shift in the centre of a normal distribution can make events in the tail (i.e. severe storms) a lot more common. I don't claim to know exactly what will happen; my claim is that the dynamics of the atmosphere under (anthropogenic) global warming is not a simple problem at all. Many thousands of good scientists work on it. And they do not need to return their PhDs. – gerrit Dec 09 '14 at 16:43
  • This is a server about physics and this problem is a physics question. It may be answered - in this case approximately - by the usual methods of physics and the answer is what I wrote. What some uncontrolled mindless computer models say or do not say is completely irrelevant. Precipitation doesn't appear in any tails. Precipitation is started when a function of the humidity, pressure, and temperature reaches a critical value that is going almost exactly through the center of the parameter space. So no strong dependence on tiny shifts of parameters is possible here. – Luboš Motl Dec 10 '14 at 07:17
  • And it is certainly not true that there are "thousands" of good scientists doing this global warming stuff - the same kind of twisting of usually elementary physics facts and laws done in order to defend the indefensible and promote risks that can't exist according to the laws of Nature - the same type of rhetorical exercises that you have just shown us. The number of good scientists who are in your discipline today could be counted by fingers on two hands. – Luboš Motl Dec 10 '14 at 07:19
  • The probability distribution of precipitation events is strongly non-linear. It certainly does have a tail. The system overall is highly non-linear and a small shift in climate certainly can have large consequences for extreme precipitation events. – gerrit Dec 10 '14 at 16:18
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    Climate science, such as compiled by the IPCC AR5 WG1 report, is based on many thousands of peer-reviewed publications, including Nature and Science, by established scientists with PhDs in physical sciences, including physics. The consensus is that there is strong evidence for antropogenic global warming. The models are (as all models) obviously incomplete, but the basic greenhouse effect physics is relatively simple. So unless you believe there is a giant conspiracy going on, you should write down why it's all wrong and publish it in a reputable journal. If it passes peer review, that is. – gerrit Dec 10 '14 at 16:21
  • Someone may be "established" but what's more important is whether the papers or claims are right or wrong and what you write is wrong – whether or not you may find a few hundreds other wrong people and call it "consensus". In this discussion, we were not talking about the greenhouse effect per se. You are completely distorting what happened. We were discussing about a particular extra hypothetical consequence of a warming - regardless of the reasons of the warming - and I explained why this effect is tiny enough to be unobservable. The physics is robust and you dislike it for corrupt reasons. – Luboš Motl Dec 11 '14 at 07:18
  • And I explained why I disagree with you. I would appreciate if we stick to the content and if you would not accuse me (and many other scientists) of corruption. – gerrit Dec 11 '14 at 15:57
  • I am totally sticking to the content. It is you who is, instead of discussing the physics involved in this question, trying to bully others by references to some friends of yours who don't have any valid arguments and evidence, just like you don't have, and their non-existent authority and non-existent credibility. This may be how some political or religious organizations decide about answers to scientific questions but it's not how it works in science. In science, questions are being answered by evidence, rational arguments, and calculations, not by intimidation. – Luboš Motl Dec 12 '14 at 08:21
  • You accuse me of disliking your interpretation for corrupt reasons, that I should return my PhD, and that the number of good scientists in my field can be counted on the fingers of two hands. I have indicated scientific arguments, a lot more can be found in the IPCC reports and the peer-reviewed papers those are based on. It is fine to have a different interpretation of the physics (such as Lindzen has), that is what a scientific debate means. It is not needed to make accusations. (So, Lindzen wrote a textbook. Anyone can. Does that make something "textbook material"?) – gerrit Dec 12 '14 at 17:11
  • I have only talked about the sorry state of that field because you have opened this sociological debate, it was not my initiative. You have not presented a glimpse of a problem with my physics arguments - de facto proofs - that all these effects are negligibly small and that's what matters here. ... I agree that something isn't textbook material just because someone wrote it in a book and he calls it a textbook. But these basics of atmospheric physics in Lindzen's book are textbook material. – Luboš Motl Dec 13 '14 at 07:16
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    I'm sure that there's plenty of material in Lindzen's book that is uncontroversial textbook material. However, the statement The frequency of rains that are stronger than a given threshold would drop is controversial and therefore not textbook material. It is true that I am not considering the details of the physics in these comments. I'm a climate remote sensing person, not a modeller. But as for who opened the debate — is the claim that something is textbook material a physical or a sociological claim? – gerrit Jan 07 '15 at 23:39
  • This is a physics questions-and-answer servers where people provide answers based on the accurate enough analysis of the science, not a computer modeling server where people are supposed to uncritically believe features of one computer program or another. By "textbook material", I meant objectively important basic information about a subject that someone should know. When the education system works, this physics-based classification is a sociological claim, too - people learn what's important. When the education system breaks down, the actual textbooks may deviate from the textbook material. – Luboš Motl Jan 08 '15 at 08:18
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    Well, and physically, The frequency of rains that are stronger than a given threshold would drop is an oversimplification. This may be true for some forms of rain, but it is certainly not true under all circumstances. For example, your paragraph on the pole-equator temperature difference would imply intense precipitation is more likely to occur in mid-latitude winter than in mid-latitude summer. Observations say the opposite. All models are wrong, but some are useful. A model that fails to explain simple observations may be too incomplete to be useful. Intense rain is more complicated. – gerrit Jan 08 '15 at 18:29