-Caveat Lector- http://www.science.gmu.edu/~zli/ghe.html Greenhouse Effect The greenhouse effect results from "the dirty of the atmospheric infrared window" by some atmospheric trace gases, permitting incoming solar radiation to reach th surface of the Earth unhindered but restricting the outward flow of infrared radiation. These atmospheric trace gases are referred as greenhouse gases. They absorb and reradiate this outgoing radiation, effectively storing some of the heat in the atmosphere, thus producing a net warming of the surface. The process is called the greenhouse effect. A Simplied Radiative Equilibrium Model The greenhouse effect plays a crucial role in maintaining a life-sustaining environment on the earth. If there is no greenhouse effect (suppose that there is no greenhouse gases existing in our atmosphere), the temperature of the earth is determined by the amount of incoming solar radiation that reaches and heats its surface. The amount of incoming solar radiation received at the Earth's surface is given by pi*R^2*S*(1-A), where R is the radius of the earth; S is the solar constant; and A is the albedo of the earth. (The albedo of the earth is approximately 33%.) This amount of incoming solar radiation reaches the surface of the earth and heats it to a temperature, called the effective temperture, Te. Supposing that the earth emits heat like a blackbody, each square meter of the earth's surface radiates infrared radiation according to the stefan-Boltzmann law, which states that the emission of infrared radiation is equal to o*Te^4, where o is the the Stefan- Boltzmann constant. Hence, the total amount of infrared radiation emitted by the earth's surface is equal to 4*pi*R^2*o*Te^4. Since there is a balance between the incoming solar radiation reaching the surface and the outgoing infrared radiation emitted at the surface, we may equate these two terms and solve for the effective temperture, Te. It is easy to find that Te=(S*(1- A)/4o)^(1/4) and to get the earth Te=253K. At a temperature of 253K, the earth would be a very inhospitable, frozen world. However, actual measurements indicate that the mean temperature of our planet averaged over the year and over all latitudes is about 288K, rather than 253K. This difference is due to the greenhouse effect. Variability of Global Temperature -- Global Warming? The various independent historical observational measurements conclude that the global average near-surface temperature has increased by about 0.5 degree centigrade over the past 100 years. This observed warming trend is continuing despite the influence of the Mt. Pinatubo volcanic eruption, which caused volcanic emissions to reduce incoming solar radiation for nearly two years. The likelihood that this global warming is due to primarily to natural variability is low. Scientists believe that this global warming trend is resulted from the enhanced greenhouse effect. The notion of an "enhanced" greenhouse effect refers primarily to the incremental global warming caused by the exponentially increasing concentrations of anthropogenically introduced greenhouse gases over and above the greenhouse effect caused by naturally occuring greenhouse gases. Although there exist large uncertainties, scientists suggest that the emissions of greenhouse gases and sulfate aerosols could, by the end of the next century, lead to an increase in global mean temperatures of about 1-4 degree centigrate. Potential Effects of Global Warming This global warming trend can cause a significant global climate changes. Human society is highly dependent on the Earth's climate. Climate patterns and human adaptations determine the availability of food, fresh water, and other resources for sustaining life. The social and economic characteriatics of society have also been shaped largely by adapting to the seasonal and year-to-year patterns of temperture and rainfall. Some potential effects associated with climate change are listed in the following. (from U.S. Climate Action Report) Water Resources The quality and quantity of drinking water, water availability for irrigation, industrial use, and electricity generation, and the health of fisheries may be significantly affected by changes in precipitation and increased evaporation. Increased rainfall may cause more frequent flooding. Climate change would likely add stress to major river basins worldwide. Coastal Resources A estimated 50 cm rise in sea level by the year 2100, could inundate more than 5,000 square miles of dry land and an additional 4000 square miles of wetlands in the U.S. Health Heat-stress mortality could increase due to higher temperatures over longer periods. Changing patterns of precipitation and temperature may produce new breeding sites for pests, shifting the range of infectious diseases. Agriculture Impacts of Climate change in developing countries could be significant. Forests Higher tempertures and precipitation changes could increase forest susceptibility to fire, disease, and insect damage. Energy and Transportation Warmer temperatures increase cooling demand but decrease heating requirements. Fewer disruptions of winter transportation may occur, but water transport may be affected by imcreased flooding or lowered river levels. Natural Climate Variability vs. Enhanced Greenhouse Effect One of the most important features of the global climate system is that it varies naturally on all time scales. Any climate change caused by human enhancing the greenhouse effect will take place on the top of the system which is already very variable. The question is how to identify umambiguously that changes in climate are due to the enhanced greenhouse. It is hoped that the types of climate changes induced by the enhanced greenhouse effect may produce a pattern of change -- a greenhouse "fingerprint" in the climate system that can only be adequately explained by the enhanced greenhous effect . Greenhouse Myths "Ice caps melting" -- A common myth is that sea level rises will be caused by melting polar icecaps. The sea level rises predicted for the next 40 years will be caused by ocean water expanding as it warms and by some melting of non-polar ice. "Is it hotter now?" -- Another myth is that global warming predictions are based on extrapolations past temperature rises. The forcast of future change do not depend on evidence from observations, but have been made on the basis of a primary understanding of the climate system and through the use of climate models. "Heat Islands" -- There have been claims that the measurements of global temperatures have been distorted by the "Urban Effect", with local temperature rises caused by urban development. In practice, climatologists have carefully corrected the data to account for spurious effects, like the urban heat island effect. Furthermore, other records, such as middle tropospheric measurements, observations of maritime temperatures and a world-wide retreat of mountain glaciers. "Waiting for the next ice age to solve the greenhouse effect" Typically, a order of 4 degrees centigrade change occurred over a period of about 1000 years during the ice age. The rate of temperature change resulting from the enhanced greenhouse effect is anticipated to be about 0.3 degrees centigate per decade. "Those who are 'Waiting for the next ice age to solve the greenhouse effect', will have to wait a very long time!" "Missing sink" -- Of the estimated seven billion tons of carbon from human- generated carbon dioxide going into the atmosphere each year, about three billion tons stay there. We know the oceans take up about two billion tons. Where is the remainder going? The remainder must also be going into the ocean or be taken up by living plants. Greenhouse Gases & Enhanced Greenhouse Effect Greenhouse gases include water vaper, a improtant, naturally occuring and highly varied greenhouse gas, and some atmospheric trace gases, such as carbon dioxide, methane, nitrous oxide, and CFCs. Rules Governing the Global Behavior of Trace Gases Budgets of Some Major Greenhouse Gases Rules Governing the Global Behavior of Trace Gases Mass Balance Causes of Trends Variability and Lifetime Additive Effects Mass Balance The main components that determine the characteristics of the atmospheric concentrations of a greenhouse gas are summarized in a mass balance equation. where C is the concentration at some point x at time t; S, for sources, are the emissions of the trace gas from natural or anthropogenic sources emitted either directly into the atmosphere or produced by atmospheric chemical processes (at x); L are the losses from chemical, deposition, or other processes; and T is the transport by atmospheric winds and turbulent processes. If we take an average over the whole atmosphere (over x), and apply the assumption that most processes that remove long-lived trace gases from the atmosphere tend to be proportional to the amount of the gas present, we can get where is the atmospheric lifetime. Causes of Trends According to the above stated equation, for gases once were in balance, increases occur either if the sources start increasing or if the lifetime gets longer. Variability and Lifetime Only long-lived gases have the potential for affecting the global environment. The variability of a trace gas, defined as the ratio of standard deviation of measured concentrations to the mean concentration at locations far from the sources, with some restrictions, is inversely proportional to the atmospheric lifetime. This effect arises principally because the concentrations of long- lived gases are the result of many years of accumulated emissions. Additive Effects Trace gases often individually contribute little to global warming. Their collective effects, however, can be substantial. Budgets of Some Major Greenhouse Gases Carbon Dioxide (CO2) Methane (CH4) Nitrous Oxide (N2O) Chlorofluorocarbons (CFCs) Carbon Dioxide (CO2) The global Carbon Dioxide budget is complex and involves transfer of CO2 between the atmosphere, the oceans, and the biosphere. Through the photosynthetic process, the land removes about 100 petagrams (10^15 g) of carbon in the form of CO2 per year. However, about the same quantity of carbon in the form of CO2 is added to the atmosphere each year by vegetation and soil respiration and decay. The world's oceans release about 100 Pg C in the form of CO2 into the atmosphere per year and in turn absorb about 104 Pg C each year. Most of the oceanic carbon is in the form of sedimentary carbonates. Burning of fossil fuels adds about 5 Pg C and biomass buring and deforestation add about another 2 Pg C to the atmosphere in the form of CO2 annually. By summing all of the fluxes of CO2 into and out of the atmosphere, we can find that about 3 Pg C in the form of CO2 is building up in the atmosphere each year. The average concentration of CO2 was about 290 ppmv in preindustrial times; now (1990) it is about 350 ppmv and increasing steadily at a rate of about 0.3-0.4%/yr. Since CO2 is chemically inert, it is not destroyed by photochemical or chemical processes in the atmosphere; either it is lost by transfer into the ocean or biosphere or it builds up in the atmosphere. Methane (CH4) Methane can be destroyed in the atmosphere via reaction with the hydroxyl radical (OH): CH4 + OH --> CH3 + H2O The OH radical destroys about 500 teragrams (10^12 g) of CH4 each year. The mean atmospheric life time of CH4 is about 8 years. Methane is produced in anaerobic environments by the action of methanogenic bacteria and by biomass burning. The major anaerobic enviroments that produce CH4 include wetlands (150 +/- 50 Tg/yr), rice paddies (100 +/- 50 Tg/yr), and enteric fermentation in the digestive system of cattle, sheep, ect. (100-150 Tg/yr). Biomass burning may supply 10-100 Tg CH4 /yr. Nitrous Oxide (N2O) Nitrous oxide is chemically inert in the troposphere. However, N2O is destroyed in the stratosphere via photolysis by solar radiation, which is responsible for about 90% of its destruction, and by reaction with excited atomic oxygen, O(1D), which is responsible for about 10% of its destruction: N2O + hv --> N2 + O(1D), < 341 nm N2O + O(1D) --> N2 + O2 N2O + O(1D) --> 2NO These photochemical and chemical processes destroy about 10.5 +/- 3 Tg N/yr. The mean lifetime of N2O in the atmosphere is about 150 years. Nitrous oxide is building up in the atmosphere at a rate of about 3 +/- 0.5 Tg N/yr. The global destruction rate of N2O is about 10 +/- 3 Tg N/yr. Hence, the global sources of N2O should be about 13.5 +/- 3.5 Tg N/yr. At present, there is a problem in identifying the sources of N2O of this total magnitude. Chlorofluorocarbons (CFC-11 and CFC-12) CFC-11 and CFC-12 are chemically inert in the troposphere and diffuse up to the statosphere, where they are destoryed by photolysis by solar radiation and by reaction with excited atomic oxygen. CCl3F + hv --> CCl2F + Cl, < 265 nm CCl2F2 + hv --> CClF2 + Cl, < 200 nm CCl3F + O(1D) --> CCl2F + ClO CCl2F2 + O(1D) --> CClF + ClO Climate Feedbacks on an Enhanced Greenhouse Effect Ocean Vegetation Clouds & Water Vapour Sea Ice Ocean The world's oceans have complicated reactions or feedbacks on the enhanced greenhouse effect. On one hand, they can provide sources for the increased water vapor as the earth becomes warming. On the other hand, the thermal holding capacity of the oceans would delay and effectively reduce the observed global warming. In addition, oceans play an important role in the global greenhouse gas budgets. For example, according to some estimates, the recent anthropogenic increase in atmospheric CO2 may be responsible for a large part of the recent global warming. The ocean bitoa, primarily phytoplankton, are believed to remove at least half of the anthropogenic carbon dioxide added to the atmosphere. Hence, the ocean sink of carbon dioxide is called the "biological CO2 pump". However, further knowledge about the flux of carbon between ocean and atmosphere is needed to accurately predict the consequences of the build-up of carbon dioxide. Vegetation Vegetation changes caused by a climate change would affect the hydrologic cycle and suface albedo. The biggest adverse impact of a CO2-induced climate change would be caused by changing precipitation patterns that would lead to overall lower rainfall amounts, or droughts during the growing season with increased frequency or severity. The biomass productivity is linearly related to the amount of water transpired over the course of a growing season. The high correlation has been found between the NDVI, a index of biomass productivity, and the precipitation during the growth season. Furthermore, high temperture appears to be detrimental to seed growth because it shortens the time period for this stage of growth in many plants. However, the rise of atmospheric CO2 concentration should cause increase in photosynthesis, growth and productivity of the earth's vegetation. Thus, the direct effects of rising CO2 and expected climate change should have a less adverse impact on vegetation than climate change alone. Clouds & Water Vapour Clouds are simultaneously strong downward infrared radiators and shortwave solar radiation reflectors. However, how clouds are likely to change with increased greenhouse warming is essentially unknown. Global warming will lead to an increase in the amount of water vapour in the atmosphere and because water vapour is a powerful greenhouse gas, this will lead to an increase in the warming. However, some scientists propose that tropical storm clouds would reach higher in the atmosphere under warmer conditions. Then the clouds would produce more rain thus adding less water vapour to the middle troposphere. The resulting drier middle troposhere will produce a negitive feedback to the global warming. Sea Ice Generally, increased temperture would tend to melt ice and result in increased absorption of solar energy by the ocean, a positive feedback. However, a decrease in sea ice would also lead to larger heat fluxes from the ocean to the atmosphere, a negative feedback. Thus, the interaction amoung the atmosphere, the ocean, sea ice, and the sensitivity of sea ice to climate change need to be observed and quantified. Methodology for Enhanced Greenhouse Effect Measurement & Data Because the climate change signals are subtle, i.e., 0.5 degree centigrade per 100 years as observed, or even the predicted temperature change of 1.5 to 4.5 degree centigrade in 50 years, amounting to a maximum annual rate of change of 0.09 degree centigrade per year, observational requirements for the detection of climate change and greenhouse effects are more stringent in terms of accuracy, precision, spatial coverage, and time series. Some related issues are listed in the following: Changes in instrumentation (sensor and/or calibration) Changes in location and exposure of sensors (e.g., surface stations) Changes in the methods of observation (e.g., ship measurements of sea surface temperature) Changes in computational procedures (e.g., for mean daily temperature) Changes in satellite algorithms that derive physical or geophysical parameters from spectral information Changes in data assimilation models (physics) used to compute variables or parameters that are not directly measured (e.g., fluxes of heat, momentum, water vapor). None of the existing observational systems were designed, implemented, or operated to directly and automatically provide our needed long-term calibrated data with global coverage for climate change studies. Furthermore, it is necessary to obtain high-frequency sampling, preferably several times per day, to gather meaningful statistics on rapid atmospheric processes, particularly those affecting clouds, radiation, and precipation. In order to meet these kind of requirements, the Earth Observing System (EOS) has been proposed. The measurement methods and data sets for some greenhouse effect related variables are stated in the following: Sea Surface Temperature Global Normalized Difference Vegetation Index (NDVI) Atmospheric Carbon Dioxide (CO2) and Methane (CH4) Concertrations Surface Skin Temperature Sea Surface Temperature Departures from the long-term climatological mean sea surface temperature (SST), referred to as SST anomalies, are key indictors on not only transient, or cyclical changes (e.g. the El Nino phenomenon in the equatorial Pacific) in the enviroment, but also long-term warming trends which may due to the enhanced greenhouse effect, and these changes may have serious implications for global environmental change, such as rising sea levels. The data set of sea surface temperatures (SST) during the years 1982 through 1992 is derived from both in situ (ocean based) measurements as well as global satellite observations. The in situ data consist of ship and buoy observations obtained from the National Meteorological Center, while the satellite data are collected from the Advanced Very High Resolution Radiometer (AVHRR) flown aboard the NOAA-7, NOAA-9, and NOAA-11 polar orbiting platforms. Satellite measurements of SST are based on techniques in which spaceborne infra-red and microwave radiometers detect thermally emitted radiation from the ocean surface. Determining SST from satellite data therefore requires an understanding of the processes by which electromagnetic radiation is emitted and reflected at the ocean surface, and emitted and attenuated by the atmosphere. These processes can be modeled theoretically. To minimize atmospheric effects, measurements must be made at wavelengths -- well-defined "window" regions of the infra-red and microwave spectrum, where the attenuation due to atmospheric constituents is small. Under favorable atmospheric and surface conditions, simple linear algorithms may provide reasonably accurate SST retrievals from either infra- red or microwave measurements. The algorithm equation has the form: where Ts is the SST and N is the number of channels used in the retrieval. Ti are the observed radiometric brightness temperatures at wavelength (or channel i), and the coefficients ai can be derived theoretically or by regression using independent in situ SST observations. More complex nonlinear algorithms can be constructed for higher accuracy. Global Normalized Difference Vegetation Index (NDVI) Global vegetation mapping is important for monitoring the global climate change and greenhouse effects. In order to monitor vegetation at global and continental scales, global normalized difference vegetation index (NDVI) data has been collected from the National Oceanographic and Atmospheric Administration's (NOAA) Advanced Very High Resolution Radiometer (AVHRR). The AVHRR sensor collects observations in both the red and infrared parts of the spectrum. The red spectral measurements are sensitive to the chlorophyll content of vegetation because chlorophyll causes considerable absorption of incoming radiation, and the near infrared to the mesophyll structure of leaves which leads to considerable reflectance. Since the first is an inverse relationship and the second a direct relationship, the NDVI defined as the normalized ratio (IR-Red)/(IR+Red) has close relationships with a number of vegetation attributes, such as the photosynthetic capacity of specific vegetation types, percentage vegetation cover and green leaf biomass. Thus, the NDVI has become the most commonly used remotely sensed measure of vegetation activity. Atmospheric Carbon Dioxide (CO2) and Methane (CH4) Concertrations Precise record od past and present atmospheric carbon dioxide (CO2) and methane (CH4) concertrations are critical to the studies of the greenhouse effects. There are a variety of techniques to determine past levels of the atmospheric gases, including direct measurements of trapped air in polar ice cores, indirect determinations from carbon isotopis in tree rings, and measurements of carbon and oxygen isotopic changes in carbon sediments in deep-ocean cores. The modern period of measurements can be taken through air samples at the monitoring stations around the world. Surface Skin Temperature The global surface skin temperatures can be obtained from the TOVS (TIROS Operational Vertical Sounder) data set. It was generated from data obtained from the HIRS/2 (High resolution Infrared Radiation Sounder) and MSU (Microwave Sounding Unit) instruments. The HIRS/2 instrument measures radiation emitted by the Earth-atmosphere system in 19 regions of the infrared spectrum between 3.7 and 15 microns. The MSU instrument makes passive microwave radiation measurements in four regions of the 50 GHz oxygen emission spectrum. In particular, the combination of HIRS/2 channels and MSU channels is useful in eliminating the effects of cloudiness on the satellite-observed infrared radiances, thus providing improved estimates of the surface skin temperature. Summary The enhanced greenhouse effect will result in significant chnages in local, regional, and global temperatures. Some climate models predict that the buildup of atmospheric greenhouse gases will result in significant increases in the global mean temperture, ranging from 0.8 to 4.1 K from 1980 to 2030. At or near the poles, glacial and surface ice and snow may begin to melt, raising the mean height of the world's oceans by as much as 20 cm by 2030 and 65 cm by the end of the next century. This will lead to flooding of many low-lying areas of the world presently occupied by hundreds of millions of people. Scientists are also concerned about the response of living systems, including humans, to temperture increases of up to 4 K over a period of only several decades. There are many questions and uncertainties about the impact of a global warming on our planet and its varied forms of life. A better understanding of these processes and couplings will help to better estimate the environmental, economic, and human health risks from an enhanced greenhouse effect. ANOMALOUS IMAGES http://www.anomalous-images.com <A HREF="http://www.ctrl.org/";>www.ctrl.org</A> DECLARATION & DISCLAIMER ========== CTRL is a discussion & informational exchange list. Proselytizing propagandic screeds are unwelcomed. Substance—not soap-boxing—please! These are sordid matters and 'conspiracy theory'—with its many half-truths, mis- directions and outright frauds—is used politically by different groups with major and minor effects spread throughout the spectrum of time and thought. 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