The Irkutsk Research Center of the Siberian Branch of the Russian Academy of Sciences has hosted a special session on the subject of "Climate of the Earth: Past, Present and Future". Taking part in the discussions were geologists, limnologists, astrophysicists, paleographers and biologists. Ajoint report on the causes of natural anomalies was presented by Deputy Director of the Institute of Earth Crust of the RAS Siberian Branch, Kirill Levi, Dr. Sc. (Geol., Mineralogy), Director of the Astronomical Observatory of Solar-Terrestrial Physics of the RAS Siberian Branch, S. Yazev, Cand. Sc. (Phys. & Math.) and Dr. Zadonina of the Irkutsk State University.
The history of our planet tells us about several glaciation epochs. The authors of the report on this subject point out that they occurred at average intervals of some 130 - 150 mn years and were produced by some obviously cosmic causes. One of the versions speaks of increased levels of carbon dioxide in our atmosphere in step with growing levels of solar activity over the past several millennia.
Some of the publications speak of a marked influence on the processes in nature and climate of changes in intensity of our geomagnetic field-this natural shield which protects the biosphere from hard galactic radiation. When solar activity drops, this factor, probably, increases, causing a global warming. But no convincing proofs of the above have so far been obtained. The current warming, which began more than 4 mn years ago, has been "interrupted" by periods of much milder climate.
In the 1920s Yugoslav geophysicist, M. Milankovich, suggested a mathematical hypothesis suggesting that variations of that kind are caused by changes of the main orbital parameters of the Earth and the accompanying "ups" and "downs" in the flux of solar radiation. And his calculations for the past 500 years more or less "match" the reality. Although the question remains of why there were glaciation epochs in the distant past, especially bearing in mind that warmer climatic conditions clearly prevailed in the geological history of the planet.
The authors of the report point out that our planet is what they call an open system and the conditions of its outer "shells" are strongly influenced by cosmic causes, above all the energy release of the Sun*. And that, in its turn, must depend on the presence of interstellar "dark matter" whose total mass, as was recently established, is greater by two orders of magnitude the mass of "visible" matter. And it can be responsible for fluctuations of star luminosity.
Another hypothesis proceeds from the fact of the complex rotations of the Galaxy. As a result our Solar system, moving around its core, periodically enters zones of increased density - gas-and-dust clouds. And our own luminary could remain in such an "environment" for millions and tens of millions of years. And that must have had its impact on our terrestrial processes, above all the climate.
No less important factors precipitating global anomalies are associated with "local" causes: changes in the optical properties of the atmosphere, soils and vegetation, relative "sizes" of the continents and the World Ocean, the areas of glaciers and the snow-cover, the levels in the air of aerosols, dust and hothouse gases, levels of their solubility in sea water, intensity of volcanic eruptions, etc.
Having said all that, the authors attribute the main role not to the internal, but "external" factors upsetting the even progression of processes in the biosphere. At early stages of its development the Earth was exposed to frequent and heavy blows from minor celestial bodies. This is proved by the surface of the Moon, covered with craters left from its "bombardment" by minor space objects. The "rate" of such events later dropped down. There are reasons to believe that the fall of an asteroid in Mexico some 65 mn years ago had "polluted" our atmosphere with vast volumes of dust, causing a drop of temperature on our planet, freezing of water reservoirs and large-scale destruction of the flora and fauna**.
Theoretical assessments of this kind, and the giant impact craters, astroblemas, suggest even greater catastrophes which must have taken place again and again in the distant past. And it is not impossible that these events had trig-
* See: B. Kuzhevsky, "Spotlight on the Sun", Science in Russia, No. 4, 2002. - Ed.
** See: A. Barenbaum, "Comets in Geological History of the Earth", Science in Russia, No. 4, 1988. - Ed.
gered off a succession of natural anomalies marking the start of the glaciation epochs.
A similar effect could have been produced by explosions of supernovas in remote space. One, for example, has been registered by our space probes as a most powerful outburst of gamma-activity on a neutron star located 20 thous. light years away from the Sun. The explosion pushed up the level of activity of night-time ionosphere to values typical for day-time period. As for its impact on other atmospheric phenomena, this has not yet been established.
Listed among the probable causes of global climate changes are also sharp shifts of the axis of rotation of the Earth with respect to the plane of its orbit. Similar scheme is being suggested as the cause of the natural cataclysm on Mars which had "stripped" it off its dense air cover, flowing waters and life*. But an event of that kind looks practically impossible because of the absence of forces capable of any such "acts". A radical shift of the axis of spin of a giant "flywheel" like our Earth would require vast amounts of energy. And that can hardly be generated even by a collision with a relatively big asteroid. But that would have caused the destruction of animals and plants and of the biosphere as a whole.
Summing it up, there are reasons to believe that mankind now finds itself in one of the eras of global nature-and-climate changes. And although the currently observed climate warming, which is "fuelling" endless debates among scientists** is taking place on an appreciable scale, it can hardly be called a catastrophe according to its immediate consequences. In all probability we are witnessing a short-term natural episode, which has continued for about half a century and which is approaching its climax, after which it will start to dwindle. Events of this kind took place time and again in the past, without leading to a planetary cataclysm.
The scale of variations of parameters of the atmosphere and of the Earth surface has so far remained within the range of fluctuations-local in space, or insignificant in time. And there are no tangible reasons for fears of some global events which could present a serious menace to all life on this planet.
But this conclusion of the authors of the aforesaid report does not fully fit the results of mathematical (cybernetic) models developed by scientists in different countries***. The constantly rising levels in the atmosphere of hothouse gases, such as carbon dioxide, discharged by our industrial plants, does "fuel" climate warming and weather contrasts. Other factors of that kind include "technogenic" transformations of landscapes, formation of deserts and semi-deserts on large territories and the destruction of forests.
As for the authors of the paper under discussion, it appears that they did not pay due attention to such terrestrial and technogenic factors, while focusing on external cosmic impacts.
Science in Siberia (Nauka v Sibiri), 2004
Prepared by Rudolf BALANDIN
* See: V. Dymnikov, "Computer Models of Terrestrial Processes", Science in Russia, No. 3, 2004. - Ed.
** See: M. Litvak, I. Mitrofanov, "Martian Seasons", Science in Russia, No. 4, 2004. -Ed.
*** See: Yu. Izrael, "Threat of Climatic Catastrophe?", Science in Russia, No. 4, 2004. - Ed.
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