|The climate and the weather fundamentally affect our lives. The agricultural production is determined by the climate conditions as well as the spatial distribution of human population on the Earth´s surface. Strong weather and climate disturbances (e.g. tropical cyclones, floods or long-time droughts) affect human population in large areas. A possible change of climate has become a frequented scientific and social topic in the last several decades, as the climate change can affect the mankind on a global scale. A conflict between the climatology and the economy arises from the fact, that the climate change can be reduced only by remedies with the serious economic consequences. Furthermore, such remedies should be done nowadays, when the impact of climate change is not quantificated precisely.
Inadvertent climate change
The climate naturally changes. An alternation of the warmer and colder periods in the past can be deduced e.g. from the polar ice or from the deep-ocean sediments. The last glacial period finished approximately 12 000 years ago, currently we are situated in the warmer period. The main reason for altering the glacial and inter-glacial periods is cyclical variation in the Earth´s movements around the Sun. The Earth rotates around the Sun in an elliptical curve whose parameters periodically change, which results in the changes of the distribution of solar radiation over the Earth´s surface. This hypothesis was deduced by Serbian scientist Milutin Milankovic in the first half of the 20th century. The paleo-climatological data confirmed a tight relation between the changes of global temperature and the changes of the elliptical curve of the Earth.
The natural changes occur slowly, the durations of glacial and inter-glacial periods are of the order of tens of thousands of years. Therefore, the mankind would probably simply adapt for such slow changes. Nevertheless, there is a concern that some human activities may cause a much faster climate change. The main such activity is the use of fossil fuels.
The greenhouse effect is a natural phenomenon necessary for the life on the Earth. The incoming solar radiation warms up the Earth´s surface and is subsequently radiated back in the form of long-wave radiation. The atmosphere naturally contains gasses capable of absorbing the heat and emitting the absorbed heat back. The amount of heat which can be emitted by an object depends on its temperature. Since the temperature in the atmosphere decreases with increasing altitude, the molecules of gasses near the upper boundary of the atmosphere emit less heat than the molecules near the surface. This is the essence of greenhouse effect – the gasses cover the Earth´s surface and increase the temperature of the atmosphere. This phenomenon was firstly described by French mathematician Jean Baptiste Fourier, which also found the analogy between the processes in the atmosphere and in a greenhouse.
The most important greenhouse gasses are carbon dioxide (CO2), methane and water vapour, which can be found naturally in the atmosphere. The air temperature near the surface would be below the freezing point without them, thus the greenhouse gasses are essential for the life on the Earth. Since the beginning of industrial revolution in the 18th century people intensively use the energy concentrated within the millions of years in fossil fuels. The burning of fossil fuels produces huge amount of carbon dioxide; the concentration of CO2 in the atmosphere incessantly grows. This can intensify the natural greenhouse effect and cause a warming of the atmosphere much faster than the natural changes.
Feedbacks in climate system
The climate system is very complicated; there are many feedbacks between its individual components. The increase of air temperature stimulates many processes which can accelerate (positive feedbacks) or attenuate (negative feedbacks) additional warming. The most important feedbacks are
Except these main feedbacks there are many other relations in the climate system, which can accelerate or attenuate warming in changing climate conditions.
The only possible way to investigate an extent and a possible impact of climate change is the detailed modelling of climate system. The model must work according to the physical laws determining the atmospheric and ocean circulation and the above mentioned feedbacks must be built in.
The climate model is a computer programme simulating the evolution of the climate system from an initial state. The structure of the model approximately corresponds to the structure of the real climate system. The model is composed of interacting components (atmosphere model, ocean model, sea ice model and surface model) and supplemented by a chemical model, which simulates the effect of compounds affecting the energy balance of the climate system (primarily CO2).
The first attempts to use the computers for climate system modelling were done many decades ago; nevertheless, the fully coupled atmospheric-ocean models are used since ´90s. Currently, the climate models represent a fundamental data source for investigation of the climate system and the climate change impact.
- the influence of water vapour (more intensive evaporation in a warmer climate increases warming)
- the influence of clouds (clouds reflect a part of incoming solar radiation, on the other hand they absorb the long-wave radiation – the overall effect depends on the type of cloud and on its distance from the surface)
- albedo (the snow and ice reflect a substantial part of incoming solar radiation; nevertheless, these surfaces will be reduced in a warmer climate which will accelerate warming)