Perhaps the most stunning discovery in the XIX century (and indeed in the history of climatology) became a phenomenon called «freezing». It turned out that thousands of years ago the huge Arctic glaciers moved inland, covering almost all of Europe and North America. By the end of the road in front of the glaciers pushed the great masses of soil and rock fragments. After reaching a maximum, they left behind a pile of rubble in the form of chains of hills — the so-called «glacial moraines,» whose origin is a long time, geologists could not explain. As part of the «glacial hypothesis» unexplained and deep parallel grooves found on the bottom of many of the valleys, and sometimes clearly visible from space: they are «plowed» all the same glacier and they carried away large pieces of rock.
Soon after this discovery, it became clear that the «invasion» of glaciers on Earth happened more than once. Apparently, repeated ice ages in the past at regular intervals. Why is this happening — no one could explain up to the beginning of the XX century, when the puzzle solved outstanding Serbian scientist Milutin Milankovitch. During World War II he served in the General Staff of the Serbian Army, was captured by the Austro-Hungarian army and was serving sentence in Budapest. Fortunately for Milankovitch (for science), colleagues from the Hungarian Academy of Sciences created the conditions for it, and most of the war, he developed the theory of periodicity of the ice ages. His explanation — the most successful of the proposed so far — based on periodic changes in the parameters of the Earth’s orbit and the Earth’s rotation, and the associated climate change are now called «Milankovitch cycles».
According to the law of conservation of angular momentum, the direction of the axis of rotation of our planet should remain unchanged. But in the real solar system in its orientation affects the attraction of the sun, moon and other planets, has a significant influence on the Earth’s rotation and its orbital motion. This influence is expressed primarily in the phenomenon of precession — Slowly turn the Earth’s axis, which describes in space a figure close to the cone. Full turn takes about 26 thousand. Years. In our era, in June and July, when the Earth is farthest from the Sun to him turned the northern hemisphere, where the bulk of the land, and six months later the oceans that lie south of the equator, «assume» the flow of solar energy increases with rapprochement with the luminary at the perihelion. After 13 thousand. Years, the situation was reversed: the northern hemisphere will be turned to the Sun in January, and bodies of water can not «soften» the global climate as effectively as do now the Indian and South Pacific (it is often treated as a separate Southern Ocean), as well as the ice dome of Antarctica.
In addition to the precession angle of the very earth’s equator to the plane of Earth’s orbit varies within a small range — these variations are called «nutation». Now this angle slightly greater than 23,4 °, and in the last century, it decreased by almost two arc minutes. The value of this parameter varies with a period of 41 thousand. Years, under the influence of the attraction of the moon, sun and Jupiter — a distant but massive planet.
Finally, under the influence of perturbations from the other planets with the passage of time and changing the shape of Earth’s orbit — rather, it is elliptic, numerically expressed eccentricity e (the ratio of the difference between the largest and smallest distance from the Earth to the Sun to twice the average distance). While the first two factors affect the redistribution of solar heat and light between the hemispheres, this cycle lasts about 93 thousand. Years, determines the total amount of energy received by the planet from our star; it is greater the closer the orbit circular (e = 0) .
Milankovitch mechanism described in detail the impact of each factor on the climate. For example, during periods when the northern hemisphere due to precession starts to get less heat, the snow every year for longer stays on the surface. Because it reflects sunlight well — continues to decrease energy intake, which leads to further cooling of the Earth. Over time, you accumulate a lot of snow and glaciers will move to the south — the Ice Age comes.
Such a scenario that awaits us when all three global climatic factors acting in concert. For the inhabitants of the middle latitudes of course, he does not look very optimistic, but on the whole planet, this option is far worse: the place of the Sahara, the Arabian desert, the dry highlands of Iran, Afghanistan and northern Mexico come relatively good wet subtropical with a fairly steady climate ( without big differences in temperature between winter and summer). It seems that in such good times there and little explored ancient civilizations originated. However, in general the effect of precession, nutation and eccentricity oscillations mutually compensated. Glaciers after a while retreating, and the climate returns to normal.
Over the last 3 million years, it registered a minimum period of four large-scale glaciation. The closest of them peaked about 18 thousand. Years ago. An era in which we live, the researchers defined as interglacial. But the deviations from «normal» temperatures are possible in smaller, so ive a big way — in other words, the same factors may cause not only substantial cooling, but warming. It seems that we are now seeing precisely this development.
In addition, the climate is influenced by many «non-recurrent» factors are underestimated. When volcanic eruptions into the atmosphere millions of tons of dust and the smallest dust particles remain in suspension until a few years without missing a significant portion of the earth’s surface to sunlight. In 1991, Mount Pinatubo in the Philippines «enrich» a few cubic kilometers of air dust particles separated stratospheric winds throughout most of the world. Created shielding effect of confidence recorded over the next four years, and was the cause of a local minimum temperature observed in the mid-90s of the last century.
Another important product of eruptions — carbon dioxide (carbon dioxide C02). Its molecules absorbing light quanta «reemit» them in the infrared range by heating the air. So we can approximately describe the famous «greenhouse effect.» However, in reality, the balance of this matter is more complicated -naprimer, increasing its concentration is enhanced uptake by plants that produce from it during the process of photosynthesis organic compounds. Besides, you can not always say exactly what the phenomenon first — warming or increase revenues of C02 into the atmosphere. The fact that its solubility in water is greatly reduced by increasing the average temperature of the oceans.
Recently, a special observatory in Antarctica and the Hawaiian volcano Mauna Loa, the leading continuous monitoring of carbon dioxide in the air, reaching the mark registered 400 molecules per million (ppm). Strictly speaking, it was a short-term spike, but the average annual value of this index may reach 395 ppm — against 315 ppm, measured in 1958. However, this growth is explained solely by industrial emissions, perhaps not: the most pessimistic estimates, the contribution of human activities to enhancing the natural greenhouse effect does not exceed 2%, and most of it falls on methane, CH4, which is 22 times more potent a greenhouse agent than C02. Overall, the average temperature at Earth’s surface has increased from pre-industrial era (around 1750) to 0,7 ° C. However, the Intergovernmental Panel on Climate Change (IPCC), still expressed concern about this issue and calls on the governments of developed countries not to weaken the measures to reduce greenhouse gas emissions.
Analysis of air bubbles contained in the fossil record. It shows that the carbon dioxide concentration of 400 ppm took place in the Pleistocene (3-5 million years ago). Then, the global average temperature was 3-4 ° C higher than today, and in the vicinity of the poles — even at 8 ° C. Woods reached the shoreline of the Arctic Ocean, the ocean itself was covered with a thin layer of ice in the middle of the polar night, and the sea level is 40 meters higher than the present one. In fact, with these realities of humanity will have to face if warming continues unabated. In addition to «Flood» We expect abnormally high temperatures, inevitably leading to a change in the agricultural way of life in the vast territories. As the chairman of the IPCC, Rajendra Pakauri professor at the beginning of industrialization the concentration of C02 was only 280 ppm, and the fact that for some fifteen hundred years this level has almost doubled — an obvious problem that mankind somehow have to deal with.
Even more radical in their views of Bob Ward, director of the Strategic Research Institute Grantham London School of Economics (Robert Ward, Grantham Research Institute, London School of Economics): «We create a prehistoric climate, in which humanity will face a huge catastrophic risk … only urgently reduce global emissions of C02, we will be able to avoid the consequences of climate hours return for three million years ago. «
Will the Government agreed — will become clear in 2015, when in Paris must pass the UN World Conference on Climate.