With CO2 driven global warming becoming more discredited by new scientific evidence every day, the world’s meddling climate regulators are casting about for a new gas to demonize. Last year the US Environmental Protection Agency was reportedly thinking of even classifying water vapor as a pollutant, due to its central role in global warming. Because water vapor is the dominant greenhouse gas in the atmosphere, accounting for the majority of the Earth’s natural greenhouse effect, water vapor emissions during human activities—such as the processing and burning of fossil fuels—are again coming under increasing scrutiny by government regulators.
Recent research has shown that water vapor, gaseous H2O, plays an important part in regulating Earth’s temperature. It has long been known that H2O is responsible for the majority of “greenhouse” warming. In fact, calculations show that removal of all greenhouse gases, leaving only water vapor, would decrease the absorption of infrared energy re-radiated by Earth’s surface by only 34 percent. While water vapor in the atmosphere is highly variable, ranging from only trace amounts to as much as 4%, the overall average amount of H2O has been rising in recent decades.
According to a PNAS report by B, D. Santer et al. the recent increase in water vapor is primarily due to human-caused increases in GHGs and not to solar forcing or volcanic eruptions. Satellites have observed an increase in atmospheric water vapor of about 0.41 kg/m2 per decade since 1988. Observations show the increase in water vapor is around 6 to 7.5% per degree Celsius warming of the lower atmosphere. The study described the research this way:
Results from current climate models indicate that water vapor increases of this magnitude cannot 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 anthropogenically caused changes in water vapor is identifiable with high statistical confidence in the SSM/I data. Experiments in which forcing factors are varied individually suggest that this ﬁfingerprint ‘‘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.
Here SSM/I data refers to microwave radiometry measurements made with the satellite-borne Special Sensor Microwave Imager (SSM/I). According to the researchers, the observed changes in temperature, moisture, and atmospheric circulation fit together in an internally and physically consistent way. Results from the SSM/I dataset can be seen in the figure below, taken from the paper.
The lower curve, labeled (B), represents the stratospheric aerosol optical depth (SAOD), which registers the amount of small particles in the atmosphere. SAOD can be seen to peak after after major volcanic eruptions, events that are known to have a cooling effect on climate. Naturally Santer et al. found a “discernible human influence” on water vapor levels which, of course, has implications for ongoing anthropogenic global warming. “These findings, together with related work on continental-scale river runoff, zonal mean rainfall, and surface specific humidity, suggest that there is an emerging anthropogenic signal in both the moisture content of earth’s atmosphere and in the cycling of moisture between atmosphere, land, and ocean,” they conclude. Then again, they attributed all water vapor from evaporation due to rising global temperatures rise to humans—direct emissions are another story.
The US EPA’s 2009 report on the Atmospheric Concentrations of Greenhouse Gases states, “water vapor is not tracked in this indicator, as it is generally accepted that human activities have not increased the concentration of water vapor in the atmosphere.” Furthermore, “no emissions control measures could significantly and directly affect atmospheric concentrations of water vapor.” No kidding. But this has not stopped the EPA from thinking about regulating water vapor for some time now.
According to EPA Director of the Department of Pollutant Decrees, Ray Donaldson: “Back before carbon dioxide was dangerous, we simply assumed that water vapor was also benign. But all reputable scientists now agree that the increased water vapor content of the atmosphere from such sources as burning of fuels and power plant cooling towers will also enhance the greenhouse effect, leading to potentially catastrophic warming.” Of course the EPA and various green NGOs find pollutants in every human activity. Asked for their position on the matter, Greenpolice spokesperson Rainbow Treetower stated, “Our basic policy is, if it’s good for people, it’s bad for the planet.” Thank goodness Mr. Donaldson added, “right now, we are not so concerned about the water vapor exhaled by people. That is low on our list of priorities.” I guess we can all continue to exhale.
The World Resources Institute (WRI) estimates that nearly two out of every three gallons of fresh water used in the Southeastern US is used to cool power plants. This amounts to around 40 billion gallons of water daily—about equal to the freshwater used for public supply across the entire country. One can draw similar conclusions for other regions in the developed world. During the heat waves in Europe a few years back France had to reduce output from several of its nuclear plants because for lack of cooling water. Does this mean that the EPA is right, that we humans need to rein in our H2O emissions?
When you think about the amount of energy released in a typical tropical storm, all of which comes from water vapor condensing back into liquid or solid H2O, it seems improbable that direct human water vapor emissions from cooling towers could have much of an impact on climate. To put this in perspective, a DOE white paper, “Water Vapor from Thermoelectric Power Plants, Does it Impact Climate?,” found that the total amount of water released from processing and burning all the world’s fossil fuel reserves at once would yield about 1 x 1016kg of water vapor. Spreading the effect of the conversion over 100 years gives a water vapor emissions rate of 1 x 1014kg water vapor per year. The current amount of water vapor in the atmosphere is 1.3 x 1016kg water. By this estimation, human emissions from power generation is less than 1% of the total amount of water vapor in the atmosphere or 0.02% of annual rainfall worldwide (5 x 1017kg water).
This estimate only accounts for power generation. Estimates for cooling water vapor emissions come in at around 25 gigatons per year, boosting the human “industrial activity” total to 125 gigatons, still under 1% and still just a drop in the bucket. Others would include evaporation from the surface of man-made reservoirs and waterways, but this is the beginning of a slippery slope. If you want to find the largest source of water vapor directly attributable to humans look to crop irrigation, which uses 70% of the freshwater consumed world wide. But that opens the door to arguments of how much water would have evaporated if left undisturbed.
The evaporation of irrigation water has been estimated to cause a globally averaged surface cooling of 0.15 Wm–2. The surface cooling rate can be as large as 30 Wm–2 in highly irrigated areas. Of course this means that somewhere else within the atmosphere all that latent heat will get released when the water vapor turns into precipitation. The heat doesn’t disappear, it just gets moved to somewhere else in the troposphere—this process is heat neutral with respect to total climate system energy. Besides, if the choice is between irrigation and mass starvation any would be regulators would risk being drawn and quartered. It is plain to see why even climate change fanatics have stayed clear of water vapor regulation in the past.
As it turns out, despite the clamoring of green alarmists, nuclear power plants circulate significant volumes of water in the process of generating electricity but actually consume a small amount of water relative to other uses. Nuclear power plants circulate water to cool equipment, continuously returning the water to its source—comparatively little is turned into water vapor that is released into the atmosphere. For comparison, a combined cycle gas turbine plant needs only about one third as much engineered cooling as other thermal plants, since much heat is discharged in the turbine exhaust (along with a lot of that nasty CO2).
All power plants require some type of cooling, water is just usually the most convenient method. In fact, where availability of cooling water is limited, cooling does not need to be a constraint on new nuclear generating capacity. Alternative cooling options for nuclear and other types of power plants are available, though at slightly higher cost. It also seems that the WRI report was rather selectively myopic in its comparison.
Of all the freshwater consumed in the United States, electricity generation accounts for 3.3 percent—less than half of the freshwater consumed by residential use (6.7 percent), according to the U.S. Geological Survey. What is seldom mentioned by the diehard anti-nuke crowed is that nuclear power plants consume less water per unit of energy produced than some forms of renewable energy.
Bottom line, unless you are willing to make the stretch and blame evaporation from the oceans due to the past century’s temperature rise on humans, people just are not a major impact on atmospheric water vapor. The reasons why water vapor levels rise and fall remain a mystery. In particular, scientists are at a loss to explain why variations in the stratosphere can have such an impact on temperatures at the surface. According to NOAA researcher Susan Solomon, “it’s a thin wedge of the upper atmosphere that packs a wallop from one decade to the next in a way we didn’t expect.” With science befuddled a number of climate change adherents are sticking with CO2, no matter what the research says.
Dave Britton from the UK Met Office reportedly said that the new water vapor research highlights the complexity of climate science. “But it does not challenge the basic science that carbon dioxide and other greenhouse gases released from human activity are warming the planet,” he said.
In a similar vein, Dr Vicky Pope, head of climate science at the Met Office, said: “Whatever’s causing this change from decade to decade is having an influence at the surface. But it is a small variation on top of the long term increase in man-made greenhouse gases.” While +30 to -25% doesn’t sound like a small variation to this observer, it’s good to know that many of the climate change faithful are sticking with CO2—perhaps they will all go down with that rapidly sinking ship.
Be safe, enjoy the interglacial and stay skeptical.
This article was posted: Monday, February 22, 2010 at 5:37 am