Anthropogenic factors include human activities that alter the environment and affect the climate. In some cases the causal relationship is direct and unambiguous, such as the effect of irrigation on temperature and humidity, in other cases the relationship is less obvious. Various hypotheses of human influence on climate have been discussed for many years.
The main issues today are: increasing CO2 concentrations in the atmosphere due to fuel combustion, aerosols in the atmosphere affecting its cooling, and the cement industry. Other factors such as land use, ozone depletion, animal agriculture, and deforestation are also affecting the climate.
Fuel combustion
Beginning to grow during the Industrial Revolution in the 1850s and gradually accelerating, humanity’s fuel consumption has caused the concentration of CO2 in the atmosphere to increase from ~280 ppm to 380 ppm. With this increase, the projected concentration at the end of the 21st century will be over 560 ppm. It is known that CO2 levels in the atmosphere are now higher than at any time in the last 750,000 years. Together with increasing methane concentrations, these changes predict a 1.4-5.6°C temperature rise between 1990 and 2040.
Aerosols
Anthropogenic aerosols, especially sulfates emitted from fuel combustion, are thought to influence atmospheric cooling. This property is believed to be responsible for the relative “plateau” in the temperature graph in the mid-20th century.
Cement industry
Cement production is an intense source of CO2 emissions. Carbon dioxide is produced when calcium carbonate (CaCO3) is heated to produce the cement ingredient calcium oxide (CaO or quicklime). Cement production accounts for approximately 5% of industrial process CO2 emissions (energy and industrial sectors). When cement is blended, the same amount of CO2 is absorbed from the atmosphere by the inverse reaction CaO + CO2 = CaCO3. Therefore, cement production and consumption changes only local atmospheric CO2 concentrations, without changing the mean value.
Land use
Land use has a significant impact on the climate. Irrigation, deforestation, and agriculture fundamentally change the environment. For example, an irrigated area changes the water balance. Land use can change the albedo of an individual area by changing the properties of the underlying surface and thus the amount of absorbed solar radiation.
Pastoralism
According to the UN’s 2006 report The Long Shadow of Livestock, livestock causes 18% of the world’s greenhouse gas emissions. This includes changes in land use, i.e. deforestation for grazing.