Global Warming Science -


Water Vapor / Humidity Implications for the GHG Based Global Warming Theory


[last update: 2010/05/07]



Water Vapor


Increasing atmospheric CO2 does not by itself result in significant warming. The climate models assume a significant positive feedback of increased water vapor in order to amplify the CO2 effect and achieve the future warming reported by the IPCC.


Paltridge et al: “Water vapor feedback in climate models is large and positive (Bony et al. 2006). The various model representations and parameterizations of convection, turbulent transfer, and deposition of latent heat generally maintain a more-or-less constant relative humidity (i.e., an increasing specific humidity q) at all levels in the troposphere as the planet warms. The increasing q amplifies the response of surface temperature to increasing CO2 by a factor of 2 or more.” (Paltridge et al: “Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data”, Theoretical Applied Climatology 2009, [])


According to the models, as the Earth warms more water evaporates from the ocean, and the amount of water vapor in the atmosphere increases. Since water vapor is the main greenhouse gas, this leads to a further increase in the atmospheric temperature. The models assume that changes in temperature and water vapor will result in a constant relative humidity (i.e. as temperatures increase, the specific humidity increases, keeping the relative humidity constant. This is one of the most controversial aspects of the models. Studies have contradictory findings regarding this. Models that include water vapor feedback with constant relative humidity predict the Earth's surface will warm more than twice as much over the next 100 years as models that contain no water vapor feedback. The water vapor feedback issue is a crucial one since without the feedback, not only are the models wrong, there can be no significant warming.




Problems With IPCC Models


According to the IPCC [] “Water vapour is also the most important gaseous source of infrared opacity in the atmosphere, accounting for about 60% of the natural greenhouse effect for clear skies, and provides the largest positive feedback in model projections of climate change.


A 2004 NASA study using satellite humidity data found that “The increases in water vapor with warmer temperatures are not large enough to maintain a constant relative humidity” resulting in overestimation of temperature increase. []


Roger Pielke provides a brief summary of the issue [] as well as a link to a research paper that states: “atmospheric temperature and water vapor trends do not follow the conjecture of constant relative humidity”.


The following figure is from the study. “A comparison of tropical temperature trends with model predictions”, by Douglass, D.H., J.R. Christy, B.D. Pearson, and S.F. Singer, 2007 - International Journal of Climatology.  [] comparing the climate models to observations from satellites and balloons (1979-2004).The models exhibit the CO2 theory characteristic of most warming occurring in the troposphere. However, the satellite and balloon based observations show warming only at the surface of the earth. The report stated: Model results and observed temperature trends are in disagreement in most of the tropical troposphere, being separated by more than twice the uncertainty of the model mean. … On the whole, the evidence indicates that model trends in the troposphere are very likely inconsistent with observations that indicate that, since 1979, there is no significant long-term amplification factor relative to the surface. If these results continue to be supported, then future projections of temperature change, as depicted in the present suite of climate models, are likely too high.”





The IPCC 2007 Report Chapter 9 – Understanding and Attributing Climate Change [] provides a climate model based simulation of the expected CO2 “spatial signature” of all forcings including anthropogenic CO2 (left-hand figure below shows degrees change per decade).  However, a study of actual data from radiosonde data shows a non-CO2 based signature []. The models predict a large tropical increase in temperature in the 300 mb range, due to increased water vapor in the troposphere. This can be seen in both the figure above and below left.



Trends in degrees per decade – left: IPCC CO2-based trend; right: actual data from radiosondes



Richard Lindzen (MIT Atmospheric Science Professor) states: “there is a much more fundamental and unambiguous check of the role of feedbacks in enhancing greenhouse warming that also shows that all models are greatly exaggerating climate sensitivity. Here, it must be noted that the greenhouse effect operates by inhibiting the cooling of the climate by reducing net outgoing radiation. However, the contribution of increasing CO2 alone does not, in fact, lead to much warming (approximately 1 deg. C for each doubling of CO2). The larger predictions from climate models are due to the fact that, within these models, the more important greenhouse substances, water vapor and clouds, act to greatly amplify whatever CO2 does. This is referred to as a positive feedback. It means that increases in surface temperature are accompanied by reductions in the net outgoing radiation – thus enhancing the greenhouse warming. ... Satellite observations of the earth’s radiation budget allow us to determine whether such a reduction does, in fact, accompany increases in surface temperature in nature. As it turns out, the satellite data from the ERBE instrument (Barkstrom, 1984, Wong et al, 2006) shows that the feedback in nature is strongly negative -- strongly reducing the direct effect of CO2 (Lindzen and Choi, 2009) in profound contrast to the model behavior.” []


A 2006 study also based on the satellite AIRS data (Pierce, Barnett, Fetzner & Gleckler: “Three-dimensional tropospheric water vapor in coupled climate models compared with observations from the AIRS satellite system”, Geophysical Research Letters, Vol 33, 2006 []) states: “The results show the models we investigated tend to have too much moisture in the upper tropospheric regions of the tropics and extra-tropics relative to the AIRS observations, by 25–100% depending on the location, and 25–50% in the zonal average. This discrepancy is well above the uncertainty in the AIRS data, and so seems to be a model problem. … this is an important finding for model simulations of future climate change, because even small absolute changes in water vapor in the upper troposphere can have a strong effect on radiative forcing


A 2008 study of the satellite-era temperature data (Christy & Douglass: “Limits on CO2 Climate Forcing from Recent Temperature Data of Earth” []). “The recent atmospheric global temperature anomalies of the Earth have been shown to consist of independent effects in different latitude bands. The tropical latitude band variations are strongly correlated with ENSO effects. …The effects in the northern extratropics are not consistent with CO2 forcing alone  … These conclusions are contrary to the IPCC [2007] statement: “[M]ost of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”” They found that the underlying trend that may be due to CO2 was 0.07 degrees per decade.


The following figure shows the relationship between the precipitation and the SST (a) and the relationship between the surface solar radiative heating and the SST (b) (Interannual anomalies of these quantities averaged over the equatorial Pacific (5S-5N, 150E-250E) and for the period July 1983—June 2001

[]) These figures compare the observations (black dots) with the output from various climate models (colored dots). The study states this confirms “common bias existing in the climate models: the overestimate of the positive feedback of water vapor. … all the models have a stronger water vapor feedback than that indicated in observations.







The study states: “The above measurements are at odds with the Global Climate Model (GCM) simulations of precipitation increase associated with rising CO2 amounts. … We find that as rainfall increases that there is not a reduction of global net radiation to space as most of the climate models have assumed. There is a weak enhancement of radiation to space with increased rainfall. We find no positive water vapor feedback. … the new climate models are making the same false assumptions as regards to water vapor feedback that was made by the global modelers of 15-20 years ago.


The following figure is from the same study.




A February 2010 report (“Is There a Missing Low Cloud Feedback in Current Climate Models?”, Graeme Stehens, Atmospheric Sciences, CSU []) states: “Radiative feedbacks involving low level clouds are a primary cause of uncertainty in global climate model projections. The feedback in models is not only uncertain in magnitude, but even its sign varies across climate models. … This reflected sunlight bias has significant implications for the cloud-climate feedback problem. The consequence is that this bias artificially suppresses the low cloud optical depth feedback in models by almost a factor of four and thus its potential role as a negative feedback.





NOAA ESRL Water Vapor Data


The NOAA Earth System Research Laboratory [] provides plots of trends of various data items from the NCEP / NCAR reanalysis database. The following figures show the specific humidity at 300, 600 and 1000 mb (1000 mb is near the earth’s surface, refer to the figure above to see that the approximate altitudes that 600 and 300 mb correspond to are roughly 15,000 and 30,000 feet).


The following figures show the specific humidity trends from 1948 to 2008 for the 300 mb (left), 600 mb (center) and 1000 mb (right) for the entire Earth. The general trend is decreasing specific humidity at 300 mb and increasing specific humidity near the Earth’s surface (1000 mb).




The following figures show similar data by latitude bands of the Earth.



Specific Humidity - 300 mb (upper troposphere)


The specific humidity at 300 mb (the altitude which should be showing the most warming according to the CO2 theory) has been decreasing for most of the world. In the southern hemisphere it has not been decreasing, but also has not increased since the 1970s.






Specific Humidity - 600 mb (mid troposphere)


The specific humidity at 600 mb was been decreasing for most of the world until the 1960s, then shows an increasing trend.





Specific Humidity - 1000 mb (near surface)


The specific humidity at 1000 mb (near the Earth’s surface) was been decreasing for the northern hemisphere, then shows an increasing trend starting around 1970. For the southern hemisphere there has been no trend since 1970.




The specific humidity has been increasing over the last few decades near the Earth’s surface (as shown by the 1000 mb data), while it has been decreasing in the upper troposphere (as shown by the 300mb data). The increase in specific humidity at the Earth’s surface (1000 mb) is related to surface temperatures. For all except the far southern hemisphere bands, the effect of the 1997/98 El Nino can be seen in the specific humidity graphs. The decreasing specific humidity in the upper troposphere (300 mb) indicates that the warming at the Earth’s surface does not match the CO2 based warming theory. This is especially so in the northern hemisphere, which has experienced most of the warming in recent decades.


A 2008 study of NCEP reanalysis data (Paltridge, Arking & Pook, “Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data”, Theoretical and Applied Climatology, Feb. 2009 []) states: “35-year trend in zonal-average annual-average specific humidity q is significantly negative at all altitudes above 850 hPa (roughly the top of the convective boundary layer) in the tropics and southern midlatitudes and at altitudes above 600 hPa in the northern midlatitudes. It is significantly positive below 850 hPa in all three zones, as might be expected in a mixed layer with rising temperatures over a moist surface. ... The upper-level negative trends in q are inconsistent with climate-model calculations ... Negative trends in q as found in the NCEP data would imply that long-term water vapor feedback is negative—that it would reduce rather than amplify the response of the climate system to external forcing such as that from increasing atmospheric CO2.


The above paper [] shows the following figure showing “(a) Southern hemisphere midlatitude monthly average specific humidity at 850 hPa as a function of time over the 35-year period 1973 to 2007. (b) Equivalent data for 400 hPa in the Northern hemisphere. The trend lines concern July/August data (square red markers) and January/February data (triangular blue markers). Green dot markers represent intermediate months



The above paper also shows the geographic distribution of specific humidity trend at 400 hPa from 1973 – 2006.



The following figures show the average annual sea surface temperature (SST) anomalies for 1973-2007 for the two regions with strongest trends in specific humidity in the figure above. The area with strongest negative trend is shown in the red line below (5N-5Sx160-180E) and the area with the strongest positive trend is shown in the blue line (0-10Nx80-100W). There has been no net warming in the area with positive specific humidity trend, while there has been slight warming in the area with the negative specific humidity trend.



(SST data from HadCRU HadSST2 database plotted at





Regional Water Vapor Patterns


Regional studies of water vapor effects tend to support the negative


Midwest US


A 2010 study reported in ScienceNews “Crop Irrigation Could be Cooling Midwest” [] states: “While average global temperatures rose about 0.74 degrees Celsius during the past century, the U.S. Midwest has experienced a noticeable slump in summer temperatures in recent decades … the recent cool temperatures seem to be part of a steady long-term decline in summertime highs in Chicago” … “Changnon suggested that fewer hot days and more precipitation are linked, because humid air warms more slowly than dry air does. One likely source of the extra moisture is the region’s agriculture. Plants pump vast amounts of water from surface soil into the atmosphere as they grow, and thirsty row crops such as corn and soybeans are much more prevalent in the region these days”.



Eastern US


Al Gore reported on his blog [] “Fact: Climate change causes more frequent and severe snowstorms Record snowstorms need two things: temperatures below freezing, and very high humidity. On a planet warmer by a few degrees on average, the Northeast US will still have plenty of days below freezing; the big difference will be warmer seas producing higher levels of moisture in the air — and therefore more severe cold-season storms."”


The following figures show the specific humidity (i.e. the amount of water) in the atmosphere from the NOAA ESRL Physical Sciences Division [] for the area of 35-45N x 70-80W (area indicated in the map). The plots are shown for the December – February time period for 4 atmospheric heights: 300mb, 400mb, 600mb, and 1000mb.


300mb (upper troposhpere - approx. 30,000 ft):

500mb (mid-troposphere - approx. 18,000 ft):

700mb (mid-troposphere - approx. 10,000 ft):

1000mb (approx. sea level):



It is clear from the above figures that winter moisture content in the atmosphere has not increased during the global warming era in the US eastern seaboard area.


The following figure shows the 700mb specific humidity for Dec – Feb for the expanded area of 25-50N x 60-80W, encompassing more ocean area for the formation of storms. No increase in moisture content (except in the 1998 El Nino year) and a definite declining trend over the last 60 years during the global warming era – the opposite of what Al Gore claims.




Al Gore blames the snowstorms on: “warmer seas producing higher levels of moisture in the air” and yet the December 2009 – February 2010 sea surface temperatures (SST) on the eastern US seaboard were mainly below average. The following figure shows the SST anomalies for the period from the NOAA ESRL web site. []



(See: for other Al Gore “Un-Truths”)