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by Oleg SOROKHTIN, Dr. Sc. (Phys. & Math.), Shirshov Institute of Oceanology, RAS
In our world of doubts and uncertainties there are, however, some very obvious "facts" which people take simply for granted. Thus, before Copernicus made his discovery in 1543 (and even long thereafter) it seemed obvious to everyone that the Sun rotates around the Earth and not the other way round. Every day everyone could see it moving across the sky from east to west, from sunrise to sunset. Today we are confronted with a similarly "obvious" situation with regard to the hothouse effect in the Earth's atmosphere. We know that the carbon dioxide contained therein, and also methane and ozone absorb the heat emanating from the warm surface of our planet, and the air warms up. Many scientists, therefore, draw the logical conclusion that the greater the volume of these gases, especially СО 2 , in the atmosphere, the warmer our climate becomes. The logic is simple and obvious. But is this really so?
Articles in this rubric reflect the opinion of the author. - Ed.
Experimental data on the dependence of temperature in the Earth's troposphere and stratosphere on the altitude (curve 4) and in the troposphere of Venus (1 and 2) in comparison with the appropriate theoretical distributions (5 and 3) built on the adiabatic theory of hothouse effect.
The idea about hothouse gases was originally suggested at the end of the 19th century by the Swedish scientist Svante August Arrhenius, and it has remained unchallenged ever since. This point of view predominates to this day in the conclusions of the Inter- Government Group of Experts on Climate Changes, of the Greenpeace organizations, the UN Program for the Environment, the World Meteorological Organization and also in the conclusions of various Russian ecological and research agencies and centers. These conclusions were also incorporated in the resolutions of the International Ecological Congresses in Rio-de-Janeiro (1992) and in Kyoto (1997). According to prognostications by proponents of this concept, by the year 2100 the mean air temperature on our planet can rise by 2.5-5 0 C, causing the level of the oceans to rise by 0.6-1 m. This can create serious problems for densely populated coastal areas, and for Russia in particular - for its gas- and oil-extracting plants in the low-lying northern regions. Other devastating consequences of global warming could include expansion of deserts, soil erosion, etc.
The governments of different countries, often yielding to pressure from ecological organizations, are forced to allocate considerable resources for the prevention of any such consequences of global climate warming, which are allegedly caused by "man- made" discharges of hothouse gases into the atmosphere. But are these costly measures really warranted? Are we really facing a tangible threat from the rising levels of CO 2 in the atmosphere?
A closer look at the situation reveals a really interesting fact: people talk a lot about the hothouse effect, but there is no theoretical substantiation thereof in our science. Different experts at different times tried to calculate the impact of rising CO 2 levels on the global climate, and they did so using different models into which they introduced numerous and not always "stable" parameters. And the greater was the number thereof, the more realistic the model was believed to be. As a result of this approach, the conclusions thus obtained turned out to be incorrect because actually the smaller is the number of the initial parameters, the more reliable is the model thus obtained.
When I tried to build a theory of the hothouse effect, it turned out that the most promising approach to the problem was a synergetic one, and its essence can be summed up in the following way The atmosphere of the Earth offers a vivid example of an open dissipating (energy scattering) system described by non-linear equations of mathematical physics. That means that within a certain scale of space and time there can occur a self-organization of physical fields and the formation of stable thermodynamic structures in it. Using this approach, one should use in calculations only the most meaningful parameters of the environment and the decisive characteristics of the governing process. For example, the averaged amounts of energy received by the Earth from solar radiation, the mean pressure of the atmosphere, its molecular weight and heat capacity One also has to take into account the effect of the negative back-feed between the albedo (reflecting capacity) of the troposphere and the mean temperature of the earth surface. In this way one can obtain the most authentic characteristics of the hothouse effect averaged for the whole of this planet.
The hothouse effect is a difference between the mean temperature of the planet's surface and its radiation (effective) temperature in space. The former all around the Earth on the average is +15 0 C and the latter is -18 0 C, which means that the hothouse effect now stands at +33 0 C. Since the Earth's atmosphere is relatively dense, in its lower (most dense) 12-km layer - the troposphere - heat is transferred not by radiation (as is believed by the champions of the "classical" - according to Svante Arrhenius - approach to the hothouse effect), but by way of convective movements of air masses, when heated air expands and goes up, and cold air is compressed and moves down. And the
Surface temperatures in the Sargasso sea (averaged ca. 50 years), determined by the isotopic sediments of oxygen on the traces of marine placton buried in bentic sediments. Horizontal line marks the mean temperature for a period of 3,000 years.
radiation transfer of heat predominates only in the stratosphere and the upper and more rarified layers.
From this one can draw the conclusion that the mean distribution of temperature in the bulk of the troposphere should be close to adiabatic, taking into account the expansion and cooling of air when rising and, on the contrary, its compression and warming up when going down. This process is regulated by atmospheric pressure and also by the effective heat capacity of air, including its additional warming due to the absorption by hothouse gases of the infrared emission of the earth's surface and emission of heat from the condensation of moisture. The latter process generates clouds which is the main factor determining the reflective capacity of the Earth. As a result, a strong negative feedback is created between near-earth and radiation temperatures, which leads to a stabilization of the heat regime of the troposphere. Indeed, any rise in the near-earth temperature boosts moisture evaporation and increases cloud cover, and this, in its turn, increases the albedo of the planet. Thus, solar heat is reflected by the clouds into space and less of that heat reaches the Earth. And the mean temperature of its surface drops down to the former level.
Apart from that, in any negative feedback in the system, the response at its output should be proportional to the effect at the input. In our case the input signal is the temperature, which characterizes solar radiation near the Earth. And this leads to another conclusion: dependent upon it linearly is the mean near-earth temperature. These two conditions (first and second conclusions) are quite enough for a confident determination of the mean temperature at any level of the terrestrial troposphere. Its distribution here, obtained with regard to the above conditions, practically fully fits a similar distribution in the troposphere of the so-called standard model of the earth's atmosphere with the mean gradient of 6.5 0 /km (this is essentially an averaged dependence of temperature on atmospheric pressure).
To verify the universality of the regularities obtained in this way I calculated the temperature for the dense CO 2 troposphere of Venus. The results turned out to be really impressive: the values obtained matched with an accuracy of 1-2 percent the temperature values registered on Venus by Soviet and US space probes. Thus it has been demonstrated that the mean temperature at any level of a dense enough troposphere of the planet (at pressure above 0.2 atm) is determined by solar radiation intensity atmospheric pressure and effective heat capacity of air.
The model thus obtained makes it possible to also assess the share of participation of all components of heat transfer in the general process of regulation of tropospheric temperature. The appropriate calculations indicate that the earth surface yields to the air masses, involved in the convective mass exchange, about 67 percent of heat, with radiation transfer adding 11 percent and another 22 percent released in condensation of moisture. And on Venus, with its much denser troposphere, the relative heating of the gas envelope by the hot surface of the planet is 55 percent lower as compared with the Earth, whereas the contribution of the radiation component to the convection turns out to be much greater - of about 45 percent.
The built model of the hothouse effect of the Earth is essentially unidimensional, showing only the dependence of the temperature on the altitude, although the planet itself looks within it as a point having no dimensions. At the same time it is the most accurate one in determining the global characteristics of the troposphere, for example, its hothouse effect, mean temperature distribution and the value of radiation or moisture-condensing components of heat emission. Applying the law of sphere illumination formulated by Lambert, and introducing the latitude of the place, this model can be translated into a bidimensional one, and using the longitude and seasonal fluctuations of the illumination of the planet - into a three-dimensional one. This, however, will be at the sacrifice of the accuracy of determining the dependence of the hothouse effect on the composition of the atmosphere.
In order to obtain local climatic characteristics, one should introduce into such models the albedo of the earth surface and the heat contribution of
Correlation of air temperature fluctuations in the Northern hemisphere (black curve) with the number ofsunspots as expressed in the Wolf numbers (red curve).
cyclones. Then one gets a clear picture of the overcooling in wintertime of territories under the anti-cyclone regions, say, in Antarctica or Yakutia. Due to the high reflecting power of the snow cover and without any additional introduction of heat, the earth's surface temperature there drops down considerably. And on the contrary, in summertime in anticyclone areas with dry air the near-earth layers become overheated (by 4-5C and more) and there occur droughts, like is often the case, for example, in trans-Volga steppes.
CO 2 ACCUMULATION - USEFUL FACTOR
Having become convinced of the correctness of the adiabatic theory of the hothouse effect, one can make several prognostication calculations. If we replace, in theory, the nitrogen-oxygen atmosphere of our planet with a CO 2 atmosphere like that on Venus (while, preserving the "terrestrial" pressure of 1 atm) the mean near-ground temperature will go down by 2 0 C and not up as is commonly assumed. During a similar imaginary replacement of the atmosphere of Venus with the nitrogen-oxygen atmosphere of the Earth (at the Venusian pressure of 91 atm), its surface temperature will rise by more than 200 0 C (from 462 0 C to 658 0 C). The conclusion which follows is that the saturation of atmosphere with CO 2 , despite its absorption of the heat radiation from the Earth, never boosts, but quite the other way round - reduces the hothouse effect and the mean surface temperature of a planet.
These, seemingly paradoxical, results are easy to explain. Remember that the heat is evacuated from the troposphere mainly through convection, and that this process is regulated by the pressure of the atmosphere and the effective heat capacity of the air. Indeed, volumes of air, heated by the absorption of infrared radiation, expand, become lighter and rapidly float upwards up to the stratosphere where they lose excessive heat through radiation emission. Thus the saturation of the atmosphere with carbon dioxide can only accelerate the convective mass exchange in the troposphere, but in no way alter its temperature regime. What is more, at the same pressures (masses) the heat capacity of the a carbon dioxide atmosphere is lower than that of a nitrogen-oxygen one. And because of the greater density of CO 2 the former turns out to be thinner and hence does not preserve so well the heat on the planet's surface as compared with the thick "fluffy blanket" of a nitrogen-oxygen atmosphere which also has a higher heat capacity.
And now, what about the impact of "man-made" discharges of carbon dioxide into the Earth's atmosphere on its climate? According to different estimates, with the combustion of natural fuels some 5-7 bln t, or 1.4-1.9 bln t of pure carbon gets into the atmosphere every year. Such colossal volumes not only reduce the heat capacity and influence the gas composition of the atmosphere, but also serve to boost its general pressure. Since both these processes proceed in the opposite directions, the mean ground surface temperature almost does not change. And this will not happen even with a twofold increase of the CO 2 concentration in the atmosphere - something expected by the year 2100. And the greater part of the CO 2 getting there is dissolved in the waters of the oceans and later, during hydration of benthic rocks, is bound up in carbonates. And some of the atmospheric oxygen can also pass into them together with carbon. In that case, instead of a small rise of atmospheric pressure one can expect its slight drop, and, consequently, just as slight cooling of the climate. And that is a far cry from its substantial warming as expected by the proponents of the "classical" stand on the hothouse effect.
Similar conclusions have been reached by many experts in the United States who are studying changes of the climate in various regions of North America. According to their findings no warming is taking place in our time. Dr. Zeitz, former President of the US National Academy of Sciences, points out that experimental findings on climate changes do not show any harmful effect of the anthropogenic uses of hydrocarbons. On the contrary, there is
tangible evidence that rising levels of carbon dioxide in the atmosphere are beneficial. The US scientists prepared a Petition of scientists to the US government urging it to withdraw from the 1997 Kyoto agreement on global climate warming and other similar accords. The Petition points out that there exists no convincing scientific evidence to the effect that anthropogenic discharges of carbon dioxide, methane or other hothouse gases are causing, or can cause in the foreseeable future, any catastrophic heating of the Earth's atmosphere or damage its climate. What is more, there is tangible scientific evidence that growing concentrations of carbon dioxide in the atmosphere are having a positive effect on the natural increment of plants and animals on our planet. By this time the Petition has been signed by tens of thousands of scientists and engineers in the United States.
Summing it up, even considerable technogenic discharges of carbon dioxide into the atmosphere of the Earth are having practically no effect on the mean values of its heat regime or the hothouse effect. What is more, mounting levels of
this gas are a beneficial factor boosting the productivity of farming and promoting the restoration of vegetation, such as in the tropical regions where forests are being felled on a massive scale.
And if the global climate is getting notably warmer, the reason for that should be looked for in something else - in the instability of oceanic currents or changes of their circulation, precision of the Earth's axis of rotation, and, finally, in fluctuations of solar activity (there is a stable correlation between the mean temperature of the Earth's surface and the number of sunspots). One should also remember that the current "centennial" climate warming started back in the 17th century, when any technogenic discharges of carbon dioxide were out of the question.
As for the climate warming of the past few decades (if it does take place) it is most probably some temporary phenomenon, some fluctuations against the background of long-time changes of the climate. Similar processes are very common in nature - such as the changing level of the Caspian Sea-after centuries of its abnormally low levels its started to rise in the mid-1980s all of a sudden and is doing so at a catastrophic pace.*
One can add that approximately from the mid-Mesozoic (150-100 mln years ago) there has been a gradual cooling of the climate on our planet which is due to the fact that nitrogen is being withdrawn from the atmosphere and bound in the nitrates and nitrites of the soil cover. At the present time this cooling is not made up for even by a gladual growth of solar radiation intensity Numerous geological data speak of the same evolutionary process, indicating that in the Mesozoic there were no glaciations on the Earth; they developed only in the middle of the Cenozoic era (some 40 mln years ago) in Antarctica, and during the past 1-2 mln years they have been periodically occurring in the Northern hemisphere. Today we find ourselves in the inter-glacial stage. But when it gives way to a new stage of glaciation it will most likely be a most severe one.
SUBSTITUTING CAUSE BY EFFECT
In discussing the problem of the hothouse effect one cannot pass in silence the arguments offered by the proponents of the idea of a direct impact of CO 2 levels upon the temperature of the Earth's troposphere. They are citing, for example, data on the levels of CO 2 gas in the ancient firn strata in Greenland and Antarctica which indicate that at the times of inter-glacial warmings the CO 2 levels in the atmosphere always rose. In their view a similar, and even stronger effect characterized the warm Cretaceous period in the Earth's history (130-60 mln years ago). But in trying to explain these phenomena, they substitute cause by effect because rising levels of CO 2 in the atmosphere were not necessarily bound to produce a warming - it could have been the result of such a warming itself. In any case, climate variations, as traced in the firn of the ice shield of Antarctica, clearly occur ahead of the matching pattern of CO 2 concentration, and that points to their primary nature. Such "leads" amount to thousands of years during which time the waters of the World Ocean - the main reservoir of CO2 on the Earth - are completely mixed over.
Everything is explained by the negative temperature dependence of CO 2 solubility in oceanic water and the Henry law on the dynamic equilibrium between the concentration of gas in the atmosphere and hydrosphere. Today the World Ocean contains some 57-60 times more carbon dioxide than the atmosphere. And if its level drops, a new equilibrium will be established at which part of CO 2 will pass into the atmosphere, or, the other way round-from the atmosphere into the ocean. But since the solubility of carbon dioxide in water drops appreciably at higher temperatures, climate warmings will always be matched by rising CO 2 levels in the atmosphere and cooling periods - by lower levels thereof.
The same can be said about the Cretaceous period. Then the mean temperature of the World Ocean was about 15 0 C higher than today, and the carbon dioxide pressure in the atmosphere, according to my estimates, was also higher than today by 1.7-2 times. But the rising CO 2 level came as a natural result of the warm climate of that time, and not at all its cause. And as for the cause, it must have been connected with a certain rise in of the atmospheric pressure in the Mesozoic era (when oxygen was generated at an increased rate following the advent and broad propagation of flowering plants on the Earth) and continental drift. As a result most of the continents during that epoch were located in the low and temperate latitudes of the planet, while the warm oceanic currents were reaching out into high latitudes, warming the coasts closer to the poles of the continents (such as Antarctida). Therefore the mean air temperature on the Earth in the Cretaceous was 2.5-3 0 C higher than today, and the climate was more even and without ice caps on the poles.
In conclusion, let me point out that quite recently President George Bush of the United States, heeding the conclusions of American scientists, decided to pull out from the Kyoto Protocol on the impact of CO 2 levels on the world climate. In my own view, it is time to reconsider our traditional views on the nature of the hothouse effect and stop trying to scare the public and the governments by some alleged severe consequences of the anthropogenic discharges of carbon dioxide and other hothouse gases. One must also understand that the accumulation of CO 2 in the Earth's atmosphere is not fraught with any dire consequences for the ecology and climate of this planet. And the benefits thereof can be substantial since carbon dioxide stimulates the development of life. Being "bread" for the green plants, it can only boost the productivity of our farming.
* See: E. Mukhina, E. Ignatov, P. Kaplin, "The Caspian: Catastrophe, Hypothesis and Strategy", Science in Russia, No. 4, 1994 . - Ed.
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