The atmospheric temperature variations do not follow the changes in the concentrations of CO2 and other trace greenhouse gases. However, they are consistent with the changes in Sun's activity, which run in cycles of 11-year and 90-years' duration. This has been known since 1982, when it was noted that in the period 1000 to 1950, the air temperature closely followed the cyclic activity of our diurnal star. (49) Data from 1865 to 1985, published in 1991, exhibited an astonishing correspondence between the temperature of the Northern Hemisphere and the 11-year cycles of the sunspot appearances, which are a measure of Sun's activity. ( 50,51) The variations in solar radiation observed between 1880 and 1993 could account for 71 percent of the global mean temperature variance (compared to 51 percent for the greenhouse gases' part alone), and correspond to a global temperature variance of about 0.4°C. (34)
However, in 1997, it suddenly became apparent that the decisive impact on climate change fluctuations comes not from the Sun, but rather from cosmic radiation. This came as a great surprise, because the energy brought to the Earth by cosmic radiation is many times smaller than that from solar radiation. The secret lies in the clouds: The impact of clouds on climate and temperature is more than a hundred times stronger than that of carbon dioxide. Even if the CO2 concentration in the air were doubled, its greenhouse effect would be cancelled by a mere 1 percent rise in cloudiness: The reason is simply that greater cloudiness means a larger deflection of the solar radiation reaching the surface of our planet. (See Variations In Cosmic Ray Intensity And Cloud Cover (1984-1994))
In 1997, Danish scientists H. Svensmark and E. Friis-Christensen noted that the changes in cloudiness measured by geostationary satellites perfectly coincide with the changes in the intensity of cosmic rays reaching the troposphere: The more intense the radiation, the more clouds. (52) Cosmic rays ionize air molecules, transforming them into condensation nuclei for water vapour, where the ice crystals — from which the clouds are created — are formed.
The quantity of cosmic radiation coming to the Earth from our galaxy and from deep space is controlled by changes in the so-called solar wind. It is created by hot plasma ejected from the solar corona to the distance of many solar diameters, carrying ionized particles and magnetic field lines. Solar wind, rushing toward the limits of the Solar System, drives galactic rays away from the Earth and makes them weaker. When the solar wind gets stronger, less cosmic radiation reaches us from space, not so many clouds are formed, and it gets warmer. When the solar wind abates, the Earth becomes cooler.
Thus, the Sun opens and closes a climate-controlling umbrella of clouds over our heads. Only in recent years have astrophysicists and physicists specializing in atmosphere research studied these phenomena and their mechanisms, in the attempt to understand them better. Perhaps, some day, we will learn to govern the clouds.
The climate is constantly changing. Alternate cycles of long cold periods and much shorter interglacial warm periods occur with some regularity. The typical length of climatic cycles in the last 2 million years was about 100,000 years, divided into 90,000 years for Ice Age periods and 10,000 years for the warm, interglacial ones. Within a given cycle, the difference in temperature between the cold and warm phases equals 3°C to 7°C. The present warm phase is probably drawing to an end—the average duration of such a phase has already been exceeded by 500 years. Transition periods between cold and warm climate phases are dramatically short: They last for only 50, 20, or even 1 to 2 years, and they appear with virtually no warning.