Greenhouse gases (GHG) trap heat in the atmosphere by reflecting radiation that the Earth emits. This increases the Earth's temperature, which is the greenhouse effect.
Greenhouse gases are required in the atmosphere to some extent. For instance, if all greenhouse gases are eliminated, the average temperature will fall by 33 °C, making it difficult for life to exist. And too much of greenhouse gases will increase the atmosphere to undesirable levels.
The primary GHG are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), chlorofluorocarbons (CFC) and ozone (O3).
It is estimated by scientists that human activities have increased the atmospheric concentration of CO2, the most harmful greenhouse gas, by 40% since the beginning of the Industrial Revolution (1750 AD).
Burning fossil fuels like oil, coal and natural gas as well as activities like livestock rearing, agriculture and deforestation push up CO2 concentration. Livestock added 14.5% of all human-caused GHG, while transportation (all vehicles and planes) added 13% yearly.
Deforestation (cutting trees) reduces absorption of carbon dioxide by plants during photosynthesis. Raising farm animals, including cattle and others such as pigs, chickens and sheep, add methane to the atmosphere.
Water vapour is the most abundant GHG causing climate change. But human activities add more water vapor to the atmosphere through industrial heating, use of cooling towers and by creating artificial lakes.
All these human activities contribute to increase in greenhouse gases and cause global warming.
If greenhouse gas emissions are not controlled, the Earth's surface temperature would cross danger level by 2047, making life on earth difficult. And it may cross the threshold of 2 °C global warming by 2036.
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