after 50 days it's back to within 1%. In this case, it is not so much underappreciated as it tends to be twisted around to imply that because water vapor is important in the system that produces climate change, then carbon dioxide is unimportant. the additional water vapour contribution would be for a given rise in Paywalled paper: An observationally based constraint on the water-vapor feedback, Gordon et al., JGR Atmospheres, R Code: CERES Water Vapor (zipped folder 750 mb), CERES Data: CERES TOA (220 Mb) and CERES Surface (115 Mb). "Why isn't water vapour acknowledged as a greenhouse gas? The range most often quoted for the equilibrium global mean surface temperature response to a doubling of CO2 concentrations in the atmosphere is 1.5°C to 4.5°C. models make regarding evaporation of water from the surface and then of If I recall correctly there seems to be a prevalent air/cloud movement from the Indian ocean across to the Atlantic. Except for the emission temperature dependence making the sides different, they would be identical. If this feedback is, in fact, substantially weaker than predicted in current models, sensitivities in the upper half of this range would be much less likely, a conclusion that would clearly have important policy implications. Do water vapour increase because temperature increased or do temperature increase because water vapour increased? There are several different ways of measuring humidity, but most non-specialists are most familiar with relative humidity, expressed in percent, and maybe dew point temperature. Richard says: Only the stratosphere is dry enough and with a long enough residence This simplifies to Water vapor and clouds account for 66 to 85 percent of the greenhouse effect, compared to a range of 9 to 26 percent for CO2. That was one example of a positive feedback, and water vapor feedback is another. Or were they looking at gaps between clouds etc. Positive temperature feedbacks amplify temperature changes. As the concentrations of other greenhouse gases, particularly carbon dioxide, increase because of human activity, it is centrally important to predict how the water vapor distribution will be affected. Here’s the math. Figure 2: Regional differences in the composition of emissions from direct and indirect emissions from agricultural production for the year 2005 in megatonnes of carbon dioxide equivalent. of course water vapor depends positively on temperature in the present state. I don’t know and I’ve never tried to to work it out. decomposition, plant reduction, methane clathrates, albedo, etc.). This combination of “new” moisture/convection mixing with an air mass already containing a relatively high moisture content may be a determining factor for the formation of tropical storms in that region. doesn't change from century to century. This corresponds to a transmittance of 15 percent or absorbance of 85 percent. However, given the Pinatubo results, the models are probably getting the The proportional trick was a good idea. This is the famed So with that out of the way, I looked at the relationship between the percentage of absorption of upwelling LW, and the temperature. Our (99% N2+O2) atmosphere is like the water, and CO2 is like the food coloring, except that the “color” of CO2 is from absorption in the invisible IR range. and Dessler, 2004) (though they still found that the feedback was S = sigma T4 the report to justify that (anyone?). Moreover, the water vapour in the total column and in the upper Thanks Good work Willis. It is a positive feedback. They found that using the observed volcanic aerosols as The overlaps complicate things, but it's clear that water vapour is daily cycling over vegetation (a few ppm), but the (very small) This is how the troposphere works. the combined changes are larger than the changes due to each individual This is because the earth warms and cools in a 24 hour cycle and of course when water vapour cools it condenses forming clouds that subsequently reduce incoming solar radiation. The errors associated with this calculation, associated primarily with the shortness of our observational time series, suggest that the long-term water vapor feedback lies between 1.9 and 2.8 W m-2 K–1. With a colder source, one would be seeing emission spectra from the parcel and with a warmer source behind the parcel, one would be seeing and absorption spectra. (Of course, using one about residence time. The principal emission bands of water vapour are 2.55 to 2.84, 5.6 to 7.6 and 12 to 25 microns when compared with those of CO2 which are 2.64 to 2.84, 4.13 to 4.5 and 13 to 17 microns the potential for absorbing LWIR, judging by its wider third band (the other bands being negligible) is much greater for wv than for CO2 molecules. shouted from the housetops. As Ramanathan saw, there’s only one greenhouse gas (GHG) that shows that kind of spatial variability of absorption, and that’s water vapor. xmlns:xsl='http://www.w3.org/1999/XSL/Transform'">. Why? Arrhenius, Fourier, and IPCC cannot handle this. The energy warming the air comes from the radiation. Funny then, how the real world observational data on climate does not reflect that Mother Nature is actually obeying the IPCC’s positive water vapour feedback mechanism. I thought one was enough; it’s not true. CO2 certainly traps a little LWIR energy, but only in proportion to its concentration, which is negligible on earth. The rule of thumb I've seen is that shorter (near-surface in the tropics). then how does this daily and variable cycling impact the Deserts also have a higher temperature range than rainforest. Then Al Gore ran for POTUS and lost, ….. and was out of a job and no prospects of getting one. In this case, unlike most such graphs, the surprising thing was the linearity. For the March 24, 2014 at 9:23 am This means that I am taking the derivative of This Is Because Higher Temperatures Cause More Evaporation And Humidity In The Atmosphere. What is measured? I first considered using theoretical blackbody calculations. @- “This gives us a value for the change in absorption of 1.8 ± .001 W/m2 per degree C.” demonstrate how quickly water reacts, I did a GCM experiment where I As in Figure 1, showing the distribution of water vapor, but this time shown as the percentage of upwelling surface longwave radiation which is absorbed in clear-sky conditions.” The atmosphere… numbers involved. Mark. emitted from the ground (380 W/m2), you get a 'trapped' portion of about So the global cloud cover has a clear overall cooling effect on the planet, even though the net effect of high and low clouds are opposite” The key word is geographic. rgbatduke says: Humidity is of course a questionable measure in and of itself, as it is usually expressed as relative humidity, water vapor content relative to saturation. Because it is so plentiful, it absorbs most of the radiation at the wavelengths where it has absorption lines, but additional water vapor can still marginally increase absorption of longwave radiation. I’ve long thought that the GHE can be better studied in places like the Namib and the Sahara than anywhere else on Earth, largely because they lack the confounding effect of water vapor. The answer is that it did not start 17 years ago, it has always been like that. The Atacama proper is in Chile. In other words, at 1°C higher temperature we should get more absorption (in W/m2) even if water vapor is fixed, simply because at a higher temperature, more longwave is radiated upward by the surface. Those, in turn, result in additional warming. nightly washed out water vapor trivial? As a result, as you point out the derivative would not be a straight line. The NCAR radiation code says that 40 ppm CO2 would be needed to get 50% of the current CO2-caused warming, rather than 20 ppm, but, either way, the lesson is clear: we’re well past the point of diminishing returns w/r/t the warming effect of CO2. Secondly,the ISCCP data since 1983 seem to disagree with the CERES data. So our emissions (or His name is Ronan Connolly. Positive feedbacks amplify (and, if large enough, destabilize) systems. That is, they work in both directions: they amplify decreases in temperature just as much as they amplify increases in temperature. Your cubic jar of colored water is only about four inches thick. Post was not sent - check your email addresses! And none of those “pie eaters” want you messin with the good deal they got going ….. and will fight you tooth n’ nail iffen you do. Making some allowance (+/-5%) for the March 24, 2014 at 1:26 am However, most scientists believe it will be a net positive feedback. According to their calculations, atmospheric water vapor amplifies warming by 2.2 plus or minus 0.4 watts per square meter per degree Celsius. stratospheric water) and, conceviably, direct deposition of water from And if I accept this as reasonably accurate figures, to wit: Models of the Earth's climate indicate that this is an important positive feedback that increases the sensitivity of surface temperatures to carbon dioxide by nearly a factor of two when considered in isolation from other feedbacks, and possibly by as much as a factor of three or more when interactions with other feedbacks are considered. Its northern extension in Peru is the Sechura Desert. (that would truncate the polar data) CO2 alone makes up between 9 and 26%, while the O3 The TOA datasets are measured. Sorry, your blog cannot share posts by email. Very interesting work http://goo.gl/iBOJkL http://www.burtonsys.com/climate/MODTRAN_etc.html chemengrls says: The constant )” The list of people whose scientific credibility approaches zero is directly related to the degree by which they stand with James Hansen’s inverted “Infrared heating model” his, and his modeler friends claim the earth operates by, So using the reasoning as noted above I would not discount what Willis has done. The boys that played with spectrums over 100 years ago had fun. If you increase water volume, this could cause further chunks of ice to outpour into the oceans.
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