by Vladimir ZUYEV, RAS Corresponding Member, deputy director for scientific work of the Institute of Monitoring of Climatic and Ecological Systems, RAS Siberian Branch (Tomsk)

What is happening with the climate of our planet? More and more often scientists fail to give a simple answer. Has modern civilization reached a potential to influence the climate or is that a great exaggeration? How much is humankind responsible for current processes? To what extent is the rise of global temperature conditioned by anthropogenic growth of the content of carbonic acid gas in the atmosphere, possessing a hothouse effect? The obvious mismatch in the dynamics of these two climatic parameters observed for the last decade is something out of the ordinary. What is in store for us in the near future--global warming and the Flood as a result of melting glaciers or a new ice age?

What we are witnessing is an acceleration of global climatic changes, deepening of climatic contrasts, increasing of frequency and amplitude of manifestations of extreme weather phenomena; hurricanes, floods, anomalously long periods of drought, resulting in forest fires. All this leads to changes of landscapes--our habitat, aggravation of stress of all living creatures on the planet. As a result there increases a probability of irrevocable losses of the weakest and unprotected biosphere links, which lead to the growth of destructive processes like an avalanche stone-fall, beginning from moving of single stones. The least protected are ecosystems of polar and subpolar regions.

In order to reasonably oppose approaching dangers, it is necessary to understand the nature of contemporary climatic changes. This task is very complicated as multilink climatic system "lithosphere-cryosphere-hydrosphere-atmosphere-biosphere" is entangled by an intricate network of direct and reverse, positive and negative links dynamically changing under an impact of both inner (terrestrial) and outer (cosmophysical and heliophysical) factors. It is impossible to take everything into

The obvious discrepancy between the trends of the global near-surface air temperature and CO₂ concentration in the atmosphere: temperature stabilization at the background of continuous accelerated CO₂ content growth.

Coincidence of periods of accelerated growth of global temperature and a serial activity of powerful tropical volcanoes. The stratospheric aerosol optical depth reconstructed according to the results of the analysis of ice cores in Greenland and Antarctica.

consideration, therefore, we have to single out the main.

In 1988, there was formed an Intergovernmental Panel on Climate Change (IPCC), consisting of specialists from 130 countries of the world. According to them, the main reason of the observed alarming processes is an anomalous growth of the content of hothouse gases in the atmosphere, first of all, of anthropogenic carbonic acid gas (CO₂). The fourth estimation report, submitted in 2007, contains an assertion that there exists 90 percent probability that climatic changes are connected with man's activities.

One of the basic arguments in favor of such assertion is based on the comparison of the data of modelling global temperature rise with the data of real observations. Some models fixed the preindustrial level of exhausts of hothouse gases and aerosols, i.e. only natural causes of climatic shifts were taken into consideration, while others additionally considered an anthropogenic factor in the form of industrial exhausts. On comparison of the results, it turned out that the first models greatly underestimate temperatures, while others coincided with real meteoobservations. But it is evident that the proposed plan of a comparative analysis initially envisaged an absolutely definite cause and effect link: growth of content of hothouse gases causes a rise of global temperature. Though a riverse situation is also equally possible, when the first of the indicated factors can be an effect of the second, in particular, at the expense of reducing the CO₂ flow into the World Ocean.

For a long time, almost for 25 years of the 20th century we were observing concerted accelerating growth both of global temperatures and atmospheric CO₂ con-

tent, which seemingly confirmed the significance of the "greenhouse effect". But, in the first decade of the 21st century, the changes in these parameters demonstrate an obvious discord: despite the accelerated growth of CO₂, we observe stabilization of temperature in the atmosphere.

It would be appropriate to remind you that cooling of the climate in 1940s-1950s took place at the background of an increase of the content of carbonic acid gas in the atmosphere, though conceding to the present one in rates. If we try to refer to the distant past about 450 mln years ago, the Ordovician*, there took place icing of huge regions of the Gondwana supercontinent at the time when the concentration of CO₂ in the atmosphere exceeded the present level by almost an order of magnitude. It is obvious that to explain climate changes only by dynamics of the carbonic acid gas content, i.e. only by "grenhouse effect" is impossible. However, given the obvious exaggeration of its role in assessment reports of IPCC (Intergovernmental Panel on Climate Change), other important factors remain almost unnoticed.

In particular, prognostic climatic models cannot fully and sufficiently correctly consider the effect of powerful volcanic eruptions in the tropical belt of latitudes. As a rule, the attitude to it is one-sided--only from the position of the change of radiation factor due to a decrease

* The Ordovician corresponds to the second period of the Paleozoic of the Earth's geological history: it began 458±1.9 mln years ago and ended 443±1.5 mln years ago.--Ed.

of solar radiation influx to the Earth's surface on its screening in the stratosphere by a volcanogenic aerosol. However, practically no one takes into account changes of the dynamic factor, arising due to continuous disturbances of atmospheric circulation--of the planetary system of air flows over the terrestrial surface. Under relatively high frequency of recurrence of powerful eruptions (at least once in 5 years), there takes place superposition of atmospheric circulation disturbances and nonlinear strengthening of the dynamic factor, i.e. synergistic effect becomes evident. Thus, it is not surprising that periods of accelerations of warmings on our planet for the last century coincide with periods of serial activity of powerful volcanoes of the tropical belt.

In order to quantitatively describe the force of this or that event and its action on the terrestrial atmosphere, the vulcanologists Chris Newhall (USA) and Stephen Self (Great Britain) suggested in 1982 a scale of volcanic eruptions--Volcanic Explosivity Index (VEI). Their classification takes into account the volume of discharged products and the height of eruptive column, i.e. gas and dust column, on top of which an eruptive cloud is formed. The VEI change range: from 0--for eruptions without an explosion, with the volume of discharges around 10^-5 km³, up to 8, when over 1,000 km³ of dust get into the atmosphere at heights more than 25 km.

Speaking about powerful volcanoes, in this article we are limited by the events with VEI from 4 to 6. In our time this category embraces eruptions of such tropical

Difference of day and night temperatures in the stratosphere over Hawaii at 30 mbar (about 23 km) during the time of perturbation (1992) and in the background period (1999).

Continuous volcanogenic depression of the stratospheric ozone in Arctic Regions in the period of serial activity of powerful tropical volcanoes (the smoothed curve of the total ozone content is shifted by 2 years forward relative to eruption chronologies).

volcanoes as Fuego (Guatemala, VEI 4) in 1974, Agung (Indonesia, VEI 5) in 1963, El Chichon (Mexico, VEI 5) in 1982, Pinatubo (Philippines, VEI 6) in 1991. In case of lesser VEI, their products, as a rule, do not get into the stratosphere, therefore their influence has a regional character. In case of events when VEI≥7, enormous quantity of products gets into the stratosphere, which are capable to essentially screen solar radiation for a long time, causing significant cooling, described by the model of "nuclear winter". For example, after eruption of the Indonesian volcano Tambora (VEI 7) in 1815, Europe registered "the year without summer", accompanied by bad harvest and hunger. While the eruption of another Indonesian volcano Toba (VEI 8), which took place around 74,000 years ago, resulted in very severe cooling (according to estimates, the temperature on our planet lowered by 10 °C), which caused a drastic drop of the number of some animals, while human population decreased from several millions to 3-10 thousands. Fortunately, such catastrophes are rather rare.

In high latitudes the volcanoes of Kamchatka, Alaska and Iceland often discharge eruption products on stratospheric heights. This is conditioned by considerably lower than in the tropics state of tropopause--a boundary line between troposphere and stratosphere. However, the volcanogenic aerosol getting to the stratosphere of high latitudes rather quickly gathers in polar zones and cannot influence the planet's climate. In case of eruptions of tropical volcanoes, eruptive clouds in the stratosphere are "spread" by winds in the same latitude belt,

The result of numerical simulation of volcanogenic heating of tropical stratosphere for temperatures near the Earth surface: formation of the center of warming on Chukotka Peninsula at the expense of the heated air mass injection from lower latitudes.

forming a long-living reservoir of aerosols, from where due to meridional circulation, wrapping the planet up like a shroud, they gradually get to polar zones. There the volcanogenic aerosol, little by little enlarging, falls on the Earth's surface and in the conditions of low temperatures gets frozen in ice. As a result, by the cores of Greenland and Antarctica there can be carried out reconstructions of the extent of volcanogenic disturbances of the global stratosphere at a depth of several thousand years ago, for example, by the parameter of optical aerosol thickness.

Due to the fact that volcanogenic aerosols strengthen reflecting power of the stratosphere, a part of solar radiation is screened and temporary decrease of global temperatures takes place. For example, in the course of the year after the Pinatubo volcano eruption, the planet's temperature dropped by almost 0.5 °C, but then the temperature returned to its previous indicators. In addition to the temporary cooling effect due to volcanogenic aerosol disturbances, there occur a number of significant phenomena in the global stratosphere, which are confirmed by instrumental observations. They are capable of causing continuous anomalies of the atmosphere's general circulation. What is meant here is, first of all, warming up of the tropical stratosphere at the heights from 18 to 24 km and of the stratospheric ozone volcanogenic depression, i.e. decrease of its content, especially in polar stratosphere, leading to its anomalous cooling.

Warming up of the tropical stratosphere is usually associated with the absorption of volcanogenic sulphuric acid aerosol of long-wave thermal radiation, emitted by the Earth's surface. But the analysis of stratospheric temperatures over Hawaiian Islands, carried out by us, have shown that in the period of volcanogenic disturbances of tropical stratosphere is registered systematic day temperature excess over night temperatures. Such phenomena are not observed in the background undisturbed periods. Thus, in July of 1992, a year after the Pinatubo volcano eruption, day temperatures on average exceeded night temperatures by 3 °C in the stratosphere over the Hawaii at the level of 30 mbar (around 23 km). As daily changes of increasing thermal radiation over the ocean are rather insignificant and in a short-wave part of the solar radiation spectrum the sulphuric acid aerosol practically does not absorb it, the observed temperature variations must be connected with the presence of certain "dark" particles, effectively absorbing Solar radiation.

In our opinion this role can be played by soot, with a high share of probability forming in the central scorching part of the eruptive column under thermal decomposition of methane, usually a part of volcanic gases. In case of breakup of the column at stratospheric heights with its transformation into an abruptly widening eruptive cloud, there are formed conditions necessary for forming of nano-sized carbon particles (high turbulence and adiabaticly low temperatures), which takes place in technological reactors for production of nano-sized particles of black carbon. Besides, the eruptive column, in essence, is a natural catalytic chemical reactor, where occur processes of Fischer-Tropsch*, i.e. in the presence of the catalyst proceeds a chemical reaction, as a result of which a mixture of monoxide of carbon (CO) and hydrogen (H₂), called gas-synthesis, transforms into hydrocarbons, first of all, methane. Both reacting components (CO and H₂) as well as Fe as a catalyst are always present in volcanic discharges. Synthesized in peripheral parts of the eruptive columns under tempera-

* Process of Fischer-Tropsch--a chemical reaction, thus called in honor of German researchers Franz Fischer and Hans Tropsch, who suggested it in the 1920s-- Ed.

Registration of losses of the Arctic Ocean ice cover from outer space in the zone of the heat center near Chukotka Peninsula (http://climatewatch.noaa.gov).

tures of 300-350 °C hydrocarbons are pulled in its central scorching part, where, according to Bernulli law*, static pressure is minimal. Here they are subjected to thermal decomposition under conditions of oxygen want with black carbon formation. In essence it is hydrophobic, but in case of oxidation of its surface it becomes rapidly hydrophilous. Therefore, in relatively "humid" lower atmosphere (troposphere) it as a sponge absorbs water, swells, becomes bigger in size and mass and rapidly settles on the Earth's surface.

In "dry" rarified stratosphere nano-sized black carbon can exist for years, which allows to explain long-term temperature and ozone anomalies, arising after powerful eruptions of tropical volcanoes. As an "absolutely black body", it actively absorbs also short-wave solar radiation, and thermal radiation of the Earth, providing effective warming up of tropical stratosphere. At least 20 significant volcanogenic aerosol disturbances of the stratosphere took place for the period of increased activity of tropical volcanoes from 1963 to 1993. It is not surprising that its temperature turned out to be on average by 2-3 °C higher than for the last two decades, during which not more than 3 such disturbances were singled out rather insignificant at that.

The considerable increase of the content of sulphuric acid aerosol in the stratosphere as a result of powerful eruptions of tropical volcanoes does not explain appearance of long-term depressions of stratospheric ozone. Probability of its disappearance during an interaction

* Bernulli law determines dependence between liquid velocity for gas) and its pressure. It is so called in honor of the 18th century Swiss physicist and mathematician Daniil Bernulli. -- Ed.

with the surface of sulphuric acid aerosol is extremely small, it is essentially lower than the level determining significant destructive influence on the stratospheric ozone layer. Soot is different. Probability of ozone destruction on its surface almost by a factor of 10² exceeds the level of significant effects on the ozonosphere. Thus, stratospheric rejection into tropical stratosphere of the nano-sized soot aerosol must lead to long depression of stratospheric ozone, which explains the multiyear negative trend of GOC (general ozone content) in the period of increased activity of tropical volcanoes and its reduction in the contemporary period, characterized by significant weakening of their activity.

As the presence of ozone in the stratosphere considerably determines its temperature mode due to absorption by it of ultraviolet solar radiation, as its decrease, most noticeable in the polar stratosphere, leads to its cooling. Thus, stratospheric rejection of nano-sized black carbon by tropical volcanoes conditions also warming up of the tropical and cooling of the polar stratosphere. Appearance of new temperature contrasts causes significant and long disturbances of general circulation of the atmosphere.

We have carried out numerical simulation of additional warming up in the tropical stratosphere at the height of 21 km by 2 °C by means of a spectral model of atmospheric circulation of intermediate complexity. It has been established that in this case for 10 years after switching off of warming up near the Earth's surface there are formed regions characterized by a pressure rise in low latitudes and its drop in high latitudes. Thus are formed conditions for a shift of heated air masses from low-latitude to high-latitude regions. As a result, there

Cumulative adding of 10-year periods of volcanogenic heating of arctic latitudes, which determined accelerated rise of global temperatures from the mid-1970s to the end of the 20th century.

Decrease of winter temperatures in the Northern Hemisphere at the end of the 21st century (according to the difference between model and control experiments).

are appearing stable contrasting temperature zones near the Earth's surface, in particular, the center of warming in the area of Chukotka Peninsula. According to observations from outer space it was here that main losses of the ice cover of the Arctic Ocean were registered. Similarity of the results of modelling and satellite data confirm the significant role of volcanogenic aerosol anomalies of tropical stratosphere in the origin of disturbances of the general circulation of the atmosphere.

If relaxation of stratospheric disturbances takes place in the course of 1.5-2 years, the anomalies of air circulation near the Earth's surface caused by them "are extinguished" according to our models, for around 10 years. Besides, for the first two years after switching off of the additional heating of the tropical stratosphere we observe insignificant cooling in high latitudes. Then, in the course of the following 8 years, there takes place heating of high latitudes at the expense of heat supercharging from subtropical regions. Under increased activity of tropical volcanoes (1963-1994) stratosphere disturbances caused by them occurred on average every 1.5 years. Cumulative adding of heat injection periods from low to high latitudes after each eruption increased growth rate of global temperatures. The analogous effect, which determined warming of the 1930s, was observed in late 19th-early 20th centuries. From 1883 to 1932 inclusive 18 powerful eruptions took place (on average every 2.8 years), including such as Krakatau (Indonesia, VEI 6) in 1883, Santa-Maria (Guatemala, VEI 6) in 1902 and Colima (Mexico, VEI 5) in 1913. In the period of rare and insignificant eruptions, on the contrary, there is registered either cooling, similar to that of the 1940s-1950s, or stabilization of temperatures, manifest for the last decade.

Stabilization of temperatures, observed nowadays under continued accelerated growth of CO₂ in the atmosphere, allows to assume an origin of a new factor of climate cooling, compensating for a "hothouse effect".

Sea ice concentration in the winter of the end of the 21st century (according to the difference between model and control experiments).

Most probably such is a change of thermohaline circulation. On the basis of two physical effects: warm water is lighter than cold and fresh water is lighter than brine, it determines meridional oceanic transfer of heat from heated low to cold high latitudes. Significant warming rates in the second half of the 20th century, caused by tropical volcanoes, resulted in active melting of arctic ice and essential desalination of the surface of northern seas. Lighter fresh water can hinder thermohaline circulation up to its complete stoppage, in particular, cut off the North-Atlantic Stream, which is a continuation of Gulf Stream and provides heat for Western Europe in winter.

We have carried out numerical simulation of switching off of meridional oceanic heat transfer in North Atlantic Regions. Research was conducted on the basis of combining two models of Max Planck Meteorological Institute (Germany): ECHAM5 and a thermodynamic model of the ocean's upper layer. The obtained results show climate cooling of the Northern Hemisphere by the end of the 21st century, especially in the north-western part of Eurasia. In winter (December-February) the temperature in all arctic regions falls on average by 7-10 °C, and besides, near Greenland, Norwegian and Barents seas it will drop by 16 °C as compared with control. Estimated assessments of sea ice concentration show that in winter all seas to the north of 55 °N will be ice-bound. In addition, due to thermal sluggishness they will fail to melt in summer and will remain practically the whole year round over 60 °N. As a result the Northern Sea Route may prove to be blocked.

Modern plans of opening up Arctic Regions are based on forecasts of global warming. All models of IPCC concerning anthropogenic influence on climate by the end of the 21st century forecast warming on average by 3.7 °C. But our model assessments tell us about a possibility of another variant of events: in case of complete stoppage of the North Atlantic Stream by the end of this century, the whole of Northern Hemisphere will get cooling on average by 2.7 °C.

At first glance, cooling by 2.7 °C cannot compensate for warming by 3.7 °C, but will only weaken it. However, in all models of IPCC temperature sensitivity to changes of concentration of hothouse gases is obviously raised too high. Therefore, stoppage of oceanic heat flow in North Atlantic Regions can lead to cooling in the Northern Hemisphere even taking into consideration the anthropogenic impact on the climate.

The above-mentioned assessments of climate cooling are indicated disregarding the influence on it of a series of powerful eruptions of tropical volcanoes. For a long period of time (several millennia) the outbursts of their serial activity took place without any visible regularity, accidentally. However, for the last 300-400 years in the context of repeated occurrence of such events we can rather accurately trace their cyclic nature with an interval of about 75 years, that's why there is a probability of occurrence of a series of powerful eruptions of tropical volcanoes in the mid-21st century. But at the background of a general tendency to cooling, this can lead only to temporary warming with return to the stage of cooling already several years after the end of the period of increased activity of tropical volcanoes.

It is important to understand that cooling as a result of changes of thermohaline circulation is a most probable consequence of the accelerated warming independent of the fact why it has happened. Therefore, topicality of scientific disputes on the priority of anthropogenic or natural factor of climatic changes is disappearing of its own accord, and the main thing becomes a problem of humankind's survival in the conditions of climate cooling and limitation of thermal energy resources.

Illustrations submitted by the author