Query: We now know that the planetary energy balance is determined by the upper levels of the troposphere and that the saturation of the absorption at the central frequency does not preclude the possibility to absorb more energy.

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Heat transfer <=SEP=> Heat transfer is a discipline of thermal engineering that concerns the generation , use , conversion , and exchange of thermal energy and heat between physical systems . Heat transfer is classified into various mechanisms , such as thermal conduction , thermal convection , thermal radiation , and transfer of energy by phase changes . Engineers also consider the transfer of mass of differing chemical species , either cold or hot , to achieve heat transfer . While these mechanisms have distinct characteristics , they often occur simultaneously in the same system .   Heat conduction , also called diffusion , is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems . When an object is at a different temperature from another body or its surroundings , heat flows so that the body and the surroundings reach the same temperature , at which point they are in thermal equilibrium . Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature , as described by the second law of thermodynamics .   Heat convection occurs when bulk flow of a fluid ( gas or liquid ) carries heat along with the flow of matter in the fluid . The flow of fluid may be forced by external processes , or sometimes ( in gravitational fields ) by buoyancy forces caused when thermal energy expands the fluid ( for example in a fire plume ) , thus influencing its own transfer . The latter process is often called `` natural convection '' . All convective processes also move heat partly by diffusion , as well . Another form of convection is forced convection . In this case the fluid is forced to flow by use of a pump , fan or other mechanical means .   Thermal radiation occurs through a vacuum or any transparent medium ( solid or fluid ) . It is the transfer of energy by means of photons in electromagnetic waves governed by the same laws .

Carbon dioxide <=SEP=> Carbon dioxide ( chemical formula ) is a colorless gas with a density about 60 % higher than that of air ( 1.225 g/L ) that is odorless at normally encountered concentrations . Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms . It occurs naturally in Earth 's atmosphere as a trace gas at a concentration of about 0.04 percent ( 400 ppm ) by volume . Natural sources include volcanoes , hot springs and geysers , and it is freed from carbonate rocks by dissolution in water and acids . Because carbon dioxide is soluble in water , it occurs naturally in groundwater , rivers and lakes , ice caps , glaciers and seawater . It is present in deposits of petroleum and natural gas .   As the source of available carbon in the carbon cycle , atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth 's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena . Plants , algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water , with oxygen produced as a waste product .   Carbon dioxide is produced by all aerobic organisms when they metabolize carbohydrates and lipids to produce energy by respiration . It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals , including humans . Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread , beer and winemaking . It is produced by combustion of wood and other organic materials and fossil fuels such as coal , peat , petroleum and natural gas .   It is a versatile industrial material , used , for example , as an inert gas in welding and fire extinguishers , as a pressurizing gas in air guns and oil recovery , as a chemical feedstock and in liquid form as a solvent in decaffeination of coffee and supercritical drying . It is added to drinking water and carbonated beverages including beer and sparkling wine to add effervescence . The frozen solid form of , known as `` dry ice '' is used as a refrigerant and as an abrasive in dry-ice blasting .   Carbon dioxide is the most significant long-lived greenhouse gas in Earth 's atmosphere . Since the Industrial Revolution anthropogenic emissions - primarily from use of fossil fuels and deforestation - have rapidly increased its concentration in the atmosphere , leading to global warming . Carbon dioxide also causes ocean acidification because it dissolves in water to form carbonic acid .

Troposphere <=SEP=> The troposphere is the lowest portion of Earth 's atmosphere , and is also where nearly all weather takes place . It contains approximately 75 % of the atmosphere 's mass and 99 % of the total mass of water vapor and aerosols . The average depths of the troposphere are 20 km in the tropics , 17 km in the mid latitudes , and 7 km in the polar regions in winter . The lowest part of the troposphere , where friction with the Earth 's surface influences air flow , is the planetary boundary layer . This layer is typically a few hundred meters to 2 km deep depending on the landform and time of day . Atop the troposphere is the tropopause , which is the border between the troposphere and stratosphere . The tropopause is an inversion layer , where the air temperature ceases to decrease with height and remains constant through its thickness .   The word troposphere derives from the for `` turn , turn toward , trope '' and '' - sphere '' ( as in , the Earth ) , reflecting the fact that rotational turbulent mixing plays an important role in the troposphere 's structure and behaviour . Most of the phenomena associated with day-to-day weather occur in the troposphere .

Ionosphere <=SEP=> The ionosphere ( -LSB- aɪˈɒnəˌsfɪər -RSB- ) is a region of Earth 's upper atmosphere , from about 60 km to 1000 km altitude , and includes the thermosphere and parts of the mesosphere and exosphere . It is ionized by solar radiation , plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere . It has practical importance because , among other functions , it influences radio propagation to distant places on the Earth .