Search

It is shown that the greenhouse gases carbon dioxide and water vapour reflect back to the surface, all IR radiation originating at the surface within their respective spectral bands. This reflection occurs in a very thin layer at the surface, not much over 12cm in thickness. Heat is lost from the surface by heat exchange with the atmosphere and by loss of radiation. About 52% of radiation leaves the surface in two principal window regions but this is not enough to account for the earth's equilibrium temperature. This window radiation seems to disappear quite quickly and is replaced by black body radiation. It is this which eventually contributes to the earth's radiation balance, and has to originate approximately between 40 and 50km altitude where the temperature is about correct, near 255K. Doubling the CO2 concentration increases the surface temperature by about 0.9°C and this need not have any influence higher up in the atmosphere. The surface temperature seems indeed to have no direct influence on the earth's external radiation balance.

This study examines the concept of ‘greenhouse gases’ and various definitions of the phenomenon known as the ‘Atmospheric Radiative Greenhouse Effect’. The six most quoted descriptions are as follows: (a) radiation trapped between the Earth’s surface and its atmosphere; (b) the insulating blanket of the atmosphere that keeps the Earth warm; (c) back radiation from the atmosphere to the Earth’s surface; (d) Infra Red absorbing gases that hinder radiative cooling and keep the surface warmer than it would otherwise be – known as ‘otherwise radiation’; (e) differences between actual surface temperatures of the Earth (as also observed on Venus) and those based on calculations; (f) any gas that absorbs infrared radiation emitted from the Earth’s surface towards free space. It is shown that none of the above descriptions can withstand the rigours of scientific scrutiny when the fundamental laws of physics and thermodynamics are applied to them.

Terrestrial planet atmospheres must be in long-term radiation balance, with solar radiation absorbed matched by thermal radiation emitted. For hot moist atmospheres, however, there is an upper limit on the thermal emission which is decoupled from the surface temperature. If net absorbed solar radiation exceeds this limit the planet will heat uncontrollably, the so-called \runaway greenhouse". Here we show that a runaway greenhouse induced steam atmosphere may be a stable state for a planet with the same amount of incident solar radiation as Earth has today, contrary to previous results. We have calculated the clear-sky radiation limits at line-by-line spectral resolution for the first time. The thermal radiation limit is lower than previously reported (282 W/sq m rather than 310W/sq m) and much more solar radiation would be absorbed (294W/sq m rather than 222W/sq m). Avoiding a runaway greenhouse under the present solar constant requires that the atmosphere is subsaturated with water, and that cloud albedo forcing exceeds cloud greenhouse forcing. Greenhouse warming could in theory trigger a runaway greenhouse but palaeoclimate comparisons suggest that foreseeable increases in greenhouse gases will be insufficient to do this.

Water-rich planets such as Earth are expected to become eventually uninhabitable, because liquid water does not remain stable at the surface as surface temperatures increase with the solar luminosity over time. Whether a large increase of atmospheric concentrations of greenhouse gases such as CO$_2$ could also destroy the habitability of water-rich planets has remained unclear. We show with three-dimensional aqua-planet numerical experiments that CO$_2$-induced forcing as readily destabilizes the climate as does solar forcing. The climate instability is caused by a positive cloud feedback. The climate does not run away, but instead attains a new steady state with global-mean sea-surface temperatures above 330 K. The upper atmosphere is considerably moister in this warm steady state than in the reference climate, implying that the planet would be subject to substantial loss of water to space. For either a certain range of elevated CO$_2$ concentrations or solar irradiation, we find both cold and warm equilibrium states, implying that the transition to the warm state may not simply be reversed by removing the additional forcing., 30 pages, 8 figures

The earth's natural climate has always been and still constantly changing. Greenhouse effect is warming of the surface of the earth by a complex process involving sunlight, trace gases and particles in the atmosphere. Some of the heat energy escapes to the space but much of it is trapped by the layers of atmospheric greenhouse gases to outer space and get absorbed. Thus the earth's lower atmosphere heats up. The greenhouse effect is a natural phenomenon and vital to life. Without the greenhouse effect the earth's average temperature would be -180C, instead of current average temperature of 150C. However, problem arise when the atmospheric concentration of greenhouse gases such as CO2, CH4, N2O, O3, halocarbons and water vapour increases.

Long-wave energy emitted by the Earth-atmosphere into space is characterized by changes in power over time that always lag behind the changes in power of the absorbed solar radiation due to slow variation in enthalpy of the Earth-atmosphere system. Long-term variation of the solar energy radiation absorbed by the Earth remains uncompensated by the energy radiated into space over the interval of time that is determined by the thermal inertia. The basic state of the climate system is when the debit and credit sides in the Earth’s global annual mean energy budget (including the air and water envelopes) are almost always unbalanced. The annual mean balance of the heat budget of the Earth-atmosphere over a long time period will reliably define the behavior and magnitude of the energy excess accumulated by the Earth or energy deficit to allow us to determine adequately and to predict beforehand the trend and amplitude of the forthcoming climate change using the prognosis of variations in the total solar irradiance (solar constant). The decrease in solar constant has been observed since the early 1990s. The Earth as a planet will have a negative balance in the energy budget in the future as well, because the Sun is entering the decline phase of the bicentennial luminosity changes. This will lead to a drop in temperature in approximately 2014. The increase in albedo and decrease in greenhouse gas concentration in the atmosphere will result in the additional decrease in absorbed portion of the solar energy and reduced greenhouse effect. The additional drop in temperature exceeding the effect of decreased solar constant can occur as a result of successive feedback effects. A deep bicentennial minimum in solar constant is to be anticipated in 2042 ± 11 and the 19th Little Ice Age (for the last 7500 years) may occur in 2055 ± 11.

The presence of atmosphere can appreciably warm a planet’s surface above the temperature of an airless environment. Known as a natural Greenhouse Effect (GE), this near-surface Atmospheric Thermal Enhancement (ATE) as named herein is presently entirely attributed to the absorption of up-welling long-wave radiation by greenhouse gases. Often quoted as 33 K for Earth, GE is estimated as a difference between planet’s observed mean surface temperature and an effective radiating temperature calculated from the globally averaged absorbed solar flux using the Stefan-Boltzmann (SB) radiation law. This approach equates a planet’s average temperature in the absence of greenhouse gases or atmosphere to an effective emission temperature assuming ATE ≡ GE. The SB law is also routinely employed to estimating the mean temperatures of airless bodies. We demonstrate that this formula as applied to spherical objects is mathematically incorrect owing to Hölder’s inequality between integrals and leads to biased results such as a significant underestimation of Earth’s ATE. We derive a new expression for the mean physical temperature of airless bodies based on an analytic integration of the SB law over a sphere that accounts for effects of regolith heat storage and cosmic background radiation on nighttime temperatures. Upon verifying our model against Moon surface temperature data provided by the NASA Diviner Lunar Radiometer Experiment, we propose it as a new analytic standard for evaluating the thermal environment of airless bodies. Physical evidence is presented that Earth’s ATE should be assessed against the temperature of an equivalent airless body such as the Moon rather than a hypothetical atmosphere devoid of greenhouse gases. Employing the new temperature formula we show that Earth’s total ATE is ~90 K, not 33 K, and that ATE = GE + TE, where GE is the thermal effect of greenhouse gases, while TE > 15 K is a thermodynamic enhancement independent of the atmospheric infrared back radiation. It is concluded that the contribution of greenhouse gases to Earth’s ATE defined as GE = ATE – TE might be greater than 33 K, but will remain uncertain until the strength of the hereto identified TE is fully quantified by future research. Electronic supplementary material The online version of this article (doi:10.1186/2193-1801-3-723) contains supplementary material, which is available to authorized users.

In this paper, we propose an analysis of the greenhouse effect on the basis of a net‐exchange formulation for clear sky atmospheres. This formulation allows access to exchanges beetwen the differents elements of the atmosphere (gas layers, the ground and space). When the greenhouse gas concentration increases, we first use a simple configuration to analyse the variations of analytic monochromatic net exchange rates. The same type of analysis is then applied to the Earth atmosphere for a clear‐sky middle latitude summer configuration with an increase in water vapour of 20% at all altitudes.

Increasing levels of certain greenhouse gases (GHGs), most importantly CO2 in the earths atmosphere, lead to climate change and global warming as a result of these gases interacting with thermal infrared (TIR) radiation from earth to space. Here, the option of modifying this radiation is analyzed which would result in modified TIR radiation that would interact less with atmospheric CO2. This alleviates the enhanced greenhouse effect, and at the same time would allow for energy recovery as heat and/or power. Power production is, of course, limited by thermodynamics Second Law. It is shown that various options exist for TIR radiation modification which may be used to generate temperature gradients or temperature differences between volumes of (gases containing) CO2 of sufficient optical thickness. This may be further exploited for power generation: a first, simple case shows power generation of ∼1 W per m2 surface at a Carnot efficiency of ∼7%, using the sky and ground level surroundings as heat reservoirs.

A common view is that the current global warming rate will continue or accelerate. But we argue that rapid warming in recent decades has been driven mainly by non-CO(2) greenhouse gases (GHGs), such as chlorofluorocarbons, CH(4), and N(2)O, not by the products of fossil fuel burning, CO(2) and aerosols, the positive and negative climate forcings of which are partially offsetting. The growth rate of non-CO(2) GHGs has declined in the past decade. If sources of CH(4) and O(3) precursors were reduced in the future, the change in climate forcing by non-CO(2) GHGs in the next 50 years could be near zero. Combined with a reduction of black carbon emissions and plausible success in slowing CO(2) emissions, this reduction of non-CO(2) GHGs could lead to a decline in the rate of global warming, reducing the danger of dramatic climate change. Such a focus on air pollution has practical benefits that unite the interests of developed and developing countries. However, assessment of ongoing and future climate change requires composition-specific long-term global monitoring of aerosol properties.

Climate is a region's general pattern and synthetic atmospheric or weather conditions over a long period. Average temperature and precipitation are the two main factors which determine a region's climate and its effect on people. Small amounts of certain gases play a key role in determining the average temperature and its climate. These gases include water vapour, carbon dioxide and synthetic chlorofluorocarbon. Together these gases are known as greenhouse gases, which allow mostly visible light and some infrared and ultraviolet radiation from the sun to pass through the troposphere. The earth's surface absorbs much of solar energy. This transforms it to longer wavelength infrared radiation which then rises into the troposphere. Some of the heat escapes into space and some is absorbed by molecules of greenhouse gases and emitted into the troposphere in the form of longer wave infrared radiation, which warms the air. This natural warming effect of troposphere is called the greenhouse effect. Human activities such as burning fossil fuels, clearing forests and growing crops release carbon dioxide, methane and nitrous oxide into the atmosphere. It is of great concern that large input of these gases into troposphere can enhance the earth's natural greenhouse effect and lead to global warming.

The Greenhouse Effect is the term applied to the warming of the earth’s surface that results from the fact that atmospheric gases have a greater transparency for incoming solar radiation than for outgoing longwave thermal radiation emitted by the earth’s surface. Ultraviolet (UV) radiation contributes little directly to this whole global radiation balance. First, UV radiation is a small fraction of extraterrestrial solar radiation, and second, much of it is absorbed in the stratosphere in comparison with other radiation components. However, ozone (O3) and chlorofluorocarbons (CFCs) are greenhouse effect gases. Ozone is important because it absorbs radiation in the middle of the “atmospheric window,” within the 8 to 12 micrometer wavelength bandwidth where many of the other standard greenhouse-effect gases (water vapor, CO2, CH4, N2O) have little effect. Tropospheric and stratospheric ozone play a role in the greenhouse effect. CFCs are important because 1) they have been recently introduced into the earth’s atmosphere, 2) they have a strong warming potential for each increment added to the atmosphere, 3) they will continue to be released to the atmosphere from emissions from closed cell foams and fugitive refrigerant gases. CFC substitutes may have their own greenhouse effect impacts.

Over 100 years ago, the Swedish chemist Svante Arrhenius first pointed out that the release of carbon dioxide into the atmosphere by the burning of fossil fuels was warming the Earth. At the time, neither he nor anybody else was particularly concerned. Greenhouse gases, such as CO2, water vapour and methane, absorb infrared radiation emitted from the Earth's surface and radiate the heat back towards the planet. The natural concentrations of these gases increase the temperature of the Earth by about 35 °C, and arc thus essential for a habitable planet.

The vertical thermal structure of a primitive terrestrial atmosphere is investigated with a radiative-convective-photochemical model. The radiative code includes the short wave contribution from water vapor and ozone, and long wave contribution from methane, carbon dioxide, water vapor and ozone. Calculations for an oxygen level of 10 −3 PAL and different CO 2 levels shows that the water vapor content, and consequently the odd hydrogen concentration, in the stratosphere is controlled by the temperature which is strongly reduced from present values due to the lower ozone content. As a result, depending on the assumed mechanism for controlling the H 2 O mixing ratio, a considerable feedback is introduced on the ozone columnar density. The same model is used to parameterize the infrared outgoing flux as a function of surface temperature to be used in a two-mode energy balance climate model. This computation is addressed to the question of whether a large amount of carbon dioxide in the primitive atmosphere could be effective in producing a greenhouse effect able to compensate for the Sun's lower luminosity. It is found that with 25 times the present carbon dioxide mixing ratio, due to the ice-albedo feedback mechanism, a decrease of 9% in the solar constant could be enough to produce an ice-covered Earth.

The present state of our knowledge of the greenhouse effect is discussed and the limitations of existing atmospheric models that are used to predict changes in the greenhouse effect are pointed out. In particular the possibly dominant effect of the cloud/radiation feedback process is mentioned. Current models predict about a 2 K rise in surface temperature for a doubling of the atmospheric CO 2 concentration and a 6 K rise if the CO 2 increased by a factor of 8 as is possible in the future if the increase in the burning of fossil fuels continues. Possible greenhouse effects due to the release of chlorofluoromethanes (c.f.ms) and aerosols into the atmosphere from man-made sources are small. Analysis of the surface temperature changes which have occurred in the Northern Hemisphere during the last 100 years are consistent with most of the changes being due to increased CO 2 and decreased stratospheric aerosol.

The influence of the expected rise of CO 2 content in our atmosphere upon terrestrial temperature is uncertain. A significant increase in temperature could be threatening to certain aspects of terrestrial biology. On the other hand, it is a general consensus among paleobiologists that the Earth possessed a CO 2 atmosphere in the past billion years, without dramatic temperature variations endangering the continuity of life. In order to clarify this problem, and to contribute to the understanding of the CO 2 greenhouse effect on Venus we have computed the absorption spectrum of CO 2 for a wide range of atmospheric concentrations. More than 2500 spectral lines of the 15 micron band were taken into account in our line-by-line calculation. We have used an empirical exponential line-shape function at the line edges. Our results agree with the experimental data of F.W. Taylor. The estimated increase in surface temperature does not reach the boiling point of water even for CO 2 concentrations thousands of times larger than the present concentrations. Higher energy (> 666 cm −1 CO 2 bands and/or an increase in atmospheric H 2 O may, however, amplify the greenhouse effect.