At the present time, much attention is paid to the study of annual cycle of surface temperature because of its significance and relevance. First of all, this has to do with the global climate changes (in particular global warming) that have occurred over the past century. Annual fluctuations of air temperature have considerable effect on the human activity (agriculture, industry). Estimation and forecasting of these fluctuations is essential for development of economy as well as prevention of any negative consequences.

It has definitely been found that the average air temperature above the Earth surface indeed is rising all over the world. As a consequence, rearrangement of global heat and moisture transfer processes takes place in the atmosphere of all the continents, which is accompanied by dramatic increase of natural disasters, such as droughts and floods, typhoons and tornados, landslides, avalanches, etc.

Greenhouse effect is considered to be the main contributor to the global warming. The point is that the Earth having received energy from the Sun generally in the visible-light spectrum emits predominantly infrared rays to the outer space. However, many atmospheric gases (water vapor, carbon dioxide, methane, nitrogen oxides, etc.) contained in the Earth’s atmosphere are transparent for visible rays and actively absorb infrared rays, thus retaining in the atmosphere some part of the heat that would transfer to the space. As a result, atmosphere gets heated.

The integral characteristic of the global climatic system based on which the intensity of temperature conditions change is estimated is represented by the global average annual temperature of the Earth’s boundary layer. It is acknowledged that the rise in air and ocean temperature globally, reduction in sea ice area, rise of sea level are obvious.

- The highest temperature rise is registered in high northern latitudes.

- Eleven of the last twelve years (including 2006) are the warmest years for the entire period of instrumental observations of global surface air temperature (since the year of 1850). Over a century, from 1907 throughout 2006, average global air temperature change was 0.74° С, at that the linear temperature trend for the last 50 years (0.13° С for a decade) was almost double the similar value for the century.

In the secular trend in global temperature anomalies (for the last 100 years) they distinguish between three periods with different patterns of temperature variation over time as follows:

1) period of initial warming in the 20th century, time interval from the beginning of the century until the 1940s: characterized by intensive temperature rise;

2) period of stabilization, from the 1940s to the 1970s;

3) period of second warming, from the 1970s up to date: yet another intensive air temperature rise is observed. The record temperature values are registered in the recent decades and even in the recent years. A number of other parameters have undergone substantial changes too:

• Considerable reduction of the ocean ice cover has occurred in the northern hemisphere over the period of the satellite observations (since 1978);
• The global average level of the World Ocean was rising for as much as 1.8 mm per year (observed since 1961). In 1993-2003, the rise already came to 3.1 mm per year. In whole, over the 20th century the level of the World Ocean had risen by 0.17 m.
• The quantity and intensity of tropical storms and other extreme weather phenomena has increased. The amount of precipitation in high latitudes has increased in the result of general activation of the global hydrological cycle;
• With the global warming, the areas of snow mantle and sea ice are decreasing and glaciers reduce in their mass and cause the rise in sea level.
• Decrease in the thickness of snow mass is going faster; deep thaw in permafrost regions is expanding.
• Heat waves are becoming more frequent and longer.
• The number of frosty days in high and middle latitudes is reducing.
• The vegetation period is getting longer. Satellite observations carried out since the early 1980s speak for the tendency of earlier “greening” of vegetation;
• Tendency of the summer aridity is reported in mid-continent regions, which is indicative of a high risk of droughts.