Since the middle of the 1970s, the average temperature of ground air in the world has been increasing with an average speed of 0.15 C per decade. The most perceptible climate changes are observed in the Arctic and subarctic zones. The on-going climate changes provoke a serious concern as they influence both the natural and economic systems and their impact on the world population becomes more and more noticeable. Due to three main factors, such as the “ocean-atmosphere” system, an anthropogenic factor and 60-year and 70-year cycles, the increase of the global temperatures leads to the global warming.
The problem of global and regional changes of environment and climate is urgent due to the amplifying influence of the anthropogenic factors, in particular, the proceeding growth of the concentration of CO2 and other greenhouse gases in the atmosphere. According to the data of the World Meteorological Organization, the quantity of the CO2 parts per million increases annually.
Fig. 1. Recent Global Monthly Mean CO2 (World Meteorological Organization (WMO, n.d.).
The Global Warming Phenomenon in the 20th Century
The phenomenon of global warming is the brightest feature of the climate change of the 20th century. The average annual global temperature of a ground layer of air has increased by 0.6 ± 0.2 C for the previous 100 years. According to the latest calculations with the use of global climatic models, it is supposed that in the 21st century, the average global air temperature will raise by 1.5-5.8 C if the concentration of CO2 doubles. The analysis of its temporary ranks allowed revealing a non-uniform nature of the global warming: there was observed increasing warming in the period between 1910 and 1946, followed by a weak cold snap in 1947-1975; however, since 1976 there has been a phase of the most intensive warming, proceeding up to the present days.
There is factorial conditionality of the noted fluctuations of the average annual air temperature. The global warming of the 20th century was provoked by the increase of frequency and intensity of a warm phase of the Southern Oscillation, while there was also a tendency to the increase of the frequency of repetition and intensity of its cold phase in the period of the cold snap in 1947-1975. A certain contribution to the fall of temperature was also made by the other factors such as the decrease in the transparency of the atmosphere, the increase of the Arctic ices, etc.
The global warming rates between 1856 - 2001 generally equaled to 0.41 C per 100 years: 0.39 C per 100 years in the Northern hemisphere and 0.43 C per 100 years in the Southern hemisphere. Thus, the nature of the genesis of climatic variability in each hemisphere is varying. According to the climatic forecasts, the rates of global warming are expected to double in the 21st century. Moreover, the fact that global warming also covers the tropical zone is the characteristic feature of the global warming of the previous decades.
The causes of climatic changes are identified based on the comparison of the observed changes with the expected reaction to the alleged external impacts recorded by means of carefully verified climatic models. Besides, it is checked whether the specified changes can be caused by some other physically possible mechanisms. The evidence of the anthropogenic impact on the climate is the dominant cause of the global warming in the 20th and 21st centuries.
The Anthropogenic Factor in the Climate Change
According to the report of the National Academy of Science, the hypothesis about the importance of the actual anthropogenic factor for the Earth climate was suggested more than a century ago. Since then, this theory had been enhanced when not only the estimations of the future changes of the climatic system, but also verification of the forecasts made some time ago became possible. Up to the middle of the 1970s, there was a long way in the development of the theory out of the hypotheses and theoretical works regarding the first model estimations of the future climatic changes with the use of the primitive computing models. However, these models gave the forecasts of global warming in the following decades which later came true.
The coherence of the observed and calculated changes in the climatic system, including global and regional values of temperature, temperature of troposphere and stratosphere, global moisture circulation, global balance of energy and changes in the cryosphere and the world ocean, specifies that the observed climate changes are caused by the increase in the concentration of atmospheric greenhouse gases provoked by the human economic activity. The amplitude and spatial structure of the observed global warming in different components are well-coordinated with the response of the climatic system to the anthropogenic and natural external influences identified by the model calculations.
The Increase of the Global Temperatures in the 21st Century
According to the estimations of the World Meteorological Organization (WMO) (n.d.), 2014 is one of the hottest years during the whole history of the world. It is substantially caused by record-breaking high global temperatures of the sea surface. High global temperatures of the sea in combination with the other factors promoted the emergence of exclusively intensive rains and floods in many countries and severe droughts in the others. In the preliminary statement of the WMO about the condition of the global climate in 2014, it is specified that the global average air temperature over the shore and the sea surfaces from January to December 2014 was approximately 0.57 C higher than the average value equaling to 14.00 C for the basic period of 1961-1990 and by 0.09 °C higher than the average value over the previous ten years (2004-2013). The average air temperature over the planet surface exceeded the average one (15.0 C) by 0.72 C in the 20th century. September of 2014 is recorded as the warmest month in a 135-year history of the WMO’s observations. The anomaly of September temperature (0.66 C) is the most perceptible during the whole period of observations, having beaten a similar record in August of 2014 (0.65 C). The greatest contribution to the anomaly of the average global temperature was made by the northwest and tropical zones of the Pacific Ocean (World Meteorological Organization (WMO), n.d.).
The global warming of the end of the 20th century and the beginning of the 21st century was the main feature characterizing modern changes of the global climate, and the global average temperature was the main indicator of the global warming. The average growth of the global warming equals to 0.166 C per 10 years for the period 1976-2013, and 0.075 C per 10 years during 1901-2013. The previous decade was characterized by a certain delay (pause) of the global warming: the global temperature fluctuates at the level of the reached high values.
The Impact of the Arctic climate on the Global Climate
The presence of the ocean and sea ice in the center of the Arctic influences the formation of the Arctic climate and defines the impact on the global climate. Therefore, a special attention is always paid to the climatic changes in the Arctic zone. The changes of air temperature over the area of the Arctic zone have been characterized by the fast increase since the end of the 1990s with an absolute record of the temperature in the summer of 2014. On the other hand, the historical data recorded since 1924 concerning the area of ice testify the reduction of the ice square in the summer in the Arctic region and its acceleration since the end of the 1990s; it is also correlated with the increase of air temperature in the Arctic zone (World Meteorological Organization (WMO, n.d.).
Fig. 2. The average surface of the sea ice in the Arctic (NSIDC). (World Meteorological Organization (WMO, n.d.).
The thickness of the sea ice in the Arctic basin has also decreased since 1980s by more than 40%, mainly owing the reduction of the amount of long-term ice. The continuation of the coordinated tendencies of the increase of air temperature and reduction of the ice area at the preservation of the observed rates of global warming indicates that the period up to 2030 can be characterized by the melting of the Arctic ice.
The revealed tendencies are coordinated with the changes of the atmospheric circulation. There is the prevalence of an anti-cyclone over the Arctic basin in the Arctic zone. In the 1990s, there was the reorganization of the circulation system, at which the cyclonic circulation over the Kara Sea, the Laptev Sea, and the area of the elevated pressure over the Canadian Arctic archipelago and Greenland was created. Such a circulation was followed by the increase of the air temperature and the strengthening of ice thawing during summer.
Within the boundaries of the World Ocean, the annual fluctuations of temperatures of the surface layer and the average atmospheric temperature are interconnected. Therefore, even idle time model calculations show the changes of the water vapor that severe greenhouse gases can add to the observed changes of air temperature. In the second half of the 20th century there has been observed the growth of the temperature of the World Ocean and reduction of the general ice cover of the Arctic Ocean. Thereof, the albedo decreases, while radiation absorbed by the ocean increases, and there is also observed the further temperature increase of the water level in the World Ocean. Thus, in high latitudes of the Northern hemisphere absorption of CO2 by the ocean decreases; on the contrary, in low latitudes, there is observed an increase in the stream of CO2 in the atmosphere. As a result, the World Ocean can act not as the global warming stabilizer, but rather as its accelerator in the climatic system.
The nonuniformity of the Earth angular velocity is the other external factor, which can influence the climatic processes. At the end of the 19th century, the temperature was lower in relation to the Earth angular velocity, while at the end of the 20th century, on the contrary, it outstripped it. Only in the middle of the 21st century (1910 - 1943), the temperature and angular speed were almost precisely in an antiphase. The global temperature increases along with the reduction of the length of the day and, respectively, there is an increase of the Earth’s rotation speed. However, the return processes have been monitored since 1943, when an angular speed has been slowed down and, respectively, the temperature has lowered.
In view of three major factors, such as the joint action of the processes in the “ocean-atmosphere” system, an anthropogenic factor, and also 60-year and 70-year cycles, it is possible to explain the reasons of the modern changes of global air temperature. During 1910-1940, there was a simultaneous increase of the global temperature at the expense of 60-year and 70-year cycles. If to consider the tendency of the temperature increase due to the increase of the concentration of greenhouse gases, the effect of warming of the 1920-40s becomes clear. Then, during the following thirty five years (1941-1975), both cycles affected the decrease of the global temperatures, while greenhouse gases influenced their increase. Therefore, the weak cold snap was noted. At last, after 1975, prior to the beginning of the 21st century all three factors temporarily coincided, and there was a sharp strengthening of the effect of the greenhouse gases, causing a perceptible increase of air temperatures if compared to the state of matters in the beginning of the 20th century. Up to 2015, the temperature was growing, but the reverse process is expected to start in 2016. However, it is impossible to claim that it will cause the process of a cold snap of climate, because the amount of the greenhouse gases is high, and the processes of large-scale interaction in the “ocean-atmosphere” system work towards the heating of the atmosphere.
The global warming does not stand still. The record heat in the combination with the pouring rains and floods led to the destruction of the means of livelihood and resulted in the destroyed lives. The most unusual and disturbing thing is that high temperatures were observed on the extensive sites of the World Ocean’s surface, including the Northern hemisphere. The record-breaking high emissions of greenhouse gases and the related concentration of greenhouse gases in the atmosphere make the future of the planet much more uncertain and gloomy.
The World Meteorological Organization and its member-countries will continue to work on the forecasts in order to improve the service and help people to cope with more frequent and destructive extreme weather and climatic conditions. Therefore, in order to keep the global temperature within the limits of 2 C and prevent the negative consequences of the climate change, it is necessary to achieve the global carbon neutrality in the 21st century. It will also help to keep the maximum quantity of carbon dioxide (CO2), which can be released into the atmosphere keeping the temperature in safe limits during the period after 2020.