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32584 Climate change

So yes, the climate has changed before humans, and in most cases scientists know why. In all cases we see the same association between CO2 levels and global temperatures. The question is, is the UN (IPCC) jumping on the bandwagon once more, with suggestions and half truths?


That's a very odd notion. Odd in two respects. First the enhanced atmospheric water vapour that follows enhanced greenhouse atmospheric warming has been directly measured  and some of the consequences with respect to surface humidity and precipitation patterns are already identified in the real world . Secondly, because the "gravity" notion raised in the dodgy website you linked to is a nonsense. Water vapour that partitions in the atmosphere does so according to atmospheric pressure and temperature, as the temperature of the atmosphere raises so does the water vapour concentration.


Is this effect countered by gravity, not to any significant degree. Atmospheric water exists in the atmosphere in the form of individual water molecules. The gravitational force acting on these molecules is extremely small and is opposed by the kinetic energy of the water molecules provided by the ambient thermal energy. It's only if the atmosphere cools a bit and the water vapour concentration rises above the saturation point, that gravity takes a significant macroscopic hold. Then water molecules "aggregate", the water vapour condenses, and gravity then has an effect (it rains!).


So not only is the website trying to sell a ludicrous notion, but it's premise is contradicted by real world measurements. The radioactive signature of upper troposphere moistening" Science 310, 841-844. Abstract: "Climate models predict that the concentration of water vapour in the upper troposphere could double by the end of the century as a result of increases in greenhouse gases. Such moistening plays a key role in amplifying the rate at which the climate warms in response to anthropogenic activities, but has been difficult to detect because of deficiencies in conventional observing systems. We use satellite measurements to highlight a distinct radioactive signature of upper troposphere moistening over the period 1982 to 2004. The observed moistening is accurately captured by climate model simulations and lends further credence to model projections of future global warming.


" Santer BD et al (2007) "Identification of human-induced changes in atmospheric moisture content" Proc. Natl. Acad. Sci. USA 104 15248-15253. Abstract: "Data from the satellite-based Special Sensor Microwave Imager (SSM/I) show that the total atmospheric moisture content over oceans has increased by 0.41 kg/m(2) per decade since 1988. Results from current climate models indicate that water vapour increases of this magnitude are not to be explained by climate noise alone. In a formal detection and attribution analysis using the pooled results from 22 different climate models, the simulated "fingerprint" pattern of anthropogenic caused changes in water vapour is identifiable with high statistical confidence in the SSM/I data. Experiments in which forcing factors are varied individually suggest that this fingerprint "match" is primarily due to human caused increases in greenhouse gases and not to solar forcing or recovery from the eruption of Mount Pinatubo. Our findings provide preliminary evidence of an emerging anthropogenic signal in the moisture content of earth's atmosphere.


" Rind D et al (1991) "Positive Water-Vapour Feedback In Climate Models Confirmed By Satellite Data" Nature 349, 500-503. Abstract: "Chief among the mechanisms thought to amplify the global climate response to increased concentrations of trace gases is the atmospheric water vapour feedback. As the oceans and atmosphere warm, there is increased evaporation, and it has been generally thought that the additional moisture then adds to the greenhouse effect by trapping more infrared radiation. Recently, it has been suggested that general circulation models used for evaluating climate change overestimate this response, and that increased convection in a warmer climate would actually dry the middle and upper troposphere by means of associated compensatory subsidence. We use some new satellite-generated water vapour data to investigate this question. From a comparison of summer and winter moisture values in regions of the middle and upper troposphere that have previously been difficult to observe with confidence, we find that, as the hemispheres warm, increased convection leads to increased water vapour above 500 mbar in approximate quantitative agreement with the results from current climate models.


The same conclusion is reached by comparing the tropical western and eastern Pacific regions. Thus, we conclude that the water vapour feedback is not overestimated in models and should amplify the climate response to increased trace-gas concentrations." [**] e.g.: Zhang XB (2007) "Detection of human influence on twentieth-century precipitation trends" Nature 448, 461-465. Abstract: "Human influence on climate has been detected in surface air temperature, sea level pressure, free atmospheric temperature, trope pause height and ocean heat content.  Human-induced changes have not, however, previously been detected in precipitation at the global scale(10-12), partly because changes in precipitation in different regions cancel each other out and thereby reduce the strength of the global average signal.


Models suggest that anthropogenic forcing should have caused a small increase in global mean precipitation and a latitudinal redistribution of precipitation, increasing precipitation at high latitudes, decreasing precipitation at sub-tropical latitudes, and possibly changing the distribution of precipitation within the tropics by shifting the position of the Inter-tropical Convergence Zone. Here we compare observed changes in land precipitation during the twentieth century averaged over latitudinal bands with changes simulated by fourteen climate models. We show that anthropogenic forcing has had a detectable influence on observed changes in average precipitation within latitudinal bands, and that these changes cannot be explained by internal climate variability or natural forcing.


We estimate that anthropogenic forcing contributed significantly to observed increases in precipitation in the Northern Hemisphere mid-latitudes, drying in the Northern Hemisphere subtropics and tropics, and moistening in the Southern Hemisphere subtropics and deep tropics. The observed changes, which are larger than estimated from model simulations, may have already had significant effects on ecosystems, agriculture and human health in regions that are sensitive to changes in precipitation, such as the Sahel. However, observational limitations have hindered a direct evaluation of model- projected changes in extreme precipitation. We used satellite observations and model simulations to examine the response of tropical precipitation events to naturally driven changes in surface temperature and atmospheric moisture content. These observations reveal a distinct link between rainfall extremes and temperature, with heavy rain events increasing during warm periods and decreasing during cold periods


It depends where you are in the atmosphere since the saturation level varies with temperature and pressure. These data are known quite accurately 'though. You can see the variation of saturation of air with water vapour as a function of temperature here. How do we know what's right or wrong?] One can compare Hoyt's assertions with reality. They don't match. Therefore in this instance we know Hoyt is wrong. A problem is that Hoyt hasn't published anything on this. he's just asserting stuff on a web site. Since he may well have written it in 2004, perhaps he thought it was correct then but doesn't realize that real world data now contradicts his assertion; perhaps he just hasn't bothered to update his web site. We'd have to ask him... Hoyt has made the assertion (on his website) that gravity effects will eliminate 90% of the warming-induced enhancement of water vapour concentrations.


It's about the evidence. In this case Hoyt is making assertions that are directly contradicted by the evidence. So in this instance Hoyt is demonstrably wrong. A lot of the efforts in dealing with so-called "sceptical" (!) "arguments" is in pointing out their inherent self-contradictions. Hoyt is also wrong (it seems to me) on straightforward theoretical/empirical grounds that relate to the competing effects of gravity and thermal kinetic energy on isolated molecules in a vapour as I outlined in my post just above.  If someone has a habit of dishonesty of course one would be foolish to take his or her word. Likewise, if someone is respected for their honesty and diligence, I'm more likely to take them at face value. I am always sceptical of stuff that is asserted on this or that web site, and if one investigates further and finds that the asserter hasn't published the relevant work. But makes assertions that are not supported by any evidence, and upon further investigation, finds that the assertions are actually directly contradicted by real world evidence, then it would be foolish not to discount the assertions.


One should be sceptical about these things! [Is there some corruption not only from the climate change sceptics but also from the IPCC and other anthropogenic climate change supporters?] Corruption is usually identifiable. There is clearly a strong agenda position to misrepresent the science amongst certain quarters (you see quite a lot of it from a cohort of posters on this web site). In my experience the only "agenda" the scientists have is to get to the bottom of whatever topic their researching, preferably making some good discoveries along the way and publishing some well-respected and highly-cited papers.


Satellite measurements from the Atmospheric Infrared Sounder (AIRS) in the upper troposphere over 4.5 yr are used to assess the co variation of upper-troposphere humidity and temperature with surface temperatures, which can be used to constrain the upper-troposphere moistening due to the water vapour feedback. Results are compared to simulations from a general circulation model, the NCAR Community Atmosphere Model (CAM), to see if the model can reproduce the variations. Results indicate that the upper troposphere maintains nearly constant relative humidity for observed perturbations to ocean surface temperatures over the observed period, with increases in temperature similar to 1.5 times the changes at the surface, and corresponding increases in water vapour ( specific humidity) of 10% -25% degrees C-1. Increases in water vapour are largest at pressures below 400 hPa, but they have a double peak structure. Simulations reproduce these changes quantitatively and qualitatively. Agreement is best when the model is sorted for satellite sampling thresholds.


This will indicates that the model reproduces the moistening associated with the observed upper-troposphere water vapour feedback. The results are not qualitatively sensitive to model resolution or model physics. We make use of microwave measurements of the tropical free troposphere relative humidity (FTH) to evaluate the extent to which the water vapour distribution in four general circulation models is faithful to reality. The comparison is performed in the tropics by sorting the FTH in dynamical regimes defined upon the 500 hPa vertical velocity. Because microwave radiation penetrates non-rainy and warm clouds, we are able to estimate the FTH over most of the dynamical regimes that characterize the tropics. The comparisons reveal that two models simulate a free troposphere drier than observed (< 10%), while the others agree with the observations. Despite some differences, the level of agreement is good enough to lend confidence in the representation of atmospheric moistening processes.


A climate change scenario, tested on two models, shows a tendency to maintain the FTH to an almost fixed value be it an ascending or a subsiding regime”. With surprising and mysterious regularity, life on Earth has flourished and vanished in cycles of mass extinction every 62 million years, say two UC Berkeley scientists who discovered the pattern after a painstaking computer study of fossil records going back for more than 500 million years. Their findings are certain to generate a renewed burst of speculation among scientists who study the history and evolution of life. Each period of abundant life and each mass extinction has itself covered at least a few million years — and the trend of biodiversity has been rising steadily ever since the last mass extinction, when dinosaurs and millions of other life forms went extinct about 65 million years ago. The Berkeley researchers are physicists, not biologists or geologists or palaeontologists, but they have analyzed the most exhaustive compendium of fossil records that exists — data that cover the first and last known appearances of no fewer than 36,380 separate marine genera, including millions of species that once thrived in the world’s seas, later virtually disappeared, and in many cases returned.


 


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