Gangotri Glacier is retreating 10-30 metres per year
Climate Change

What are the Causes of Global Warming?

Causes Of Global Warming : The accumulation of  heat trapping gases in the atmosphere is the reason of rising global temperature known as ‘global warming‘. These heat trapping gases are known as greenhouse gases.

causes of global warming

        Greenhouse Gases

  • Greenhouse gases include carbon di oxide, methane, nitrous oxide and chlorofluorocarbons etc. In the atmosphere these gases act as a blanket, trap heat radiations reflected by the earth which in their absence would go back to atmosphere and eventually increase the global temperature.

    Greenhouse Effect

  • Sun emits electromagnetic radiations. When the radiation strikes the earth surface a part of it is absorbed while rest is emitted back as infrared rays (IR). A part of these IR rays are absorbed by the greenhouse gases present in the atmosphere of the earth. First these gases absorb the infrared rays coming from earth and then emit them back in all the directions. A part of re-emitted IR rays take the direction towards the earth and increase the temperature of the earth. This is known as greenhouse effect.
  • This greenhouse effect is responsible for maintaining the average temperature on earth suitable for the life. Had these gases not been there in the atmosphere the average temperature on earth would have been -18°C which is much below the earth’s actual average temperature of 14 °C. The credit to raise the average temperature of earth up-to the level that life becomes possible goes to these green house gases.

Causes of Global Warming

  • In the industrialized world the emission of greenhouse gases have increased tremendously. This is creating a situation in which the concentration of these gases in the atmosphere is increasing continuously. This is leading to additional warming of the earth.
  • The concentration of greenhouse gases in the atmosphere depends on the rate these are being emitted and the rate at which these leaves the atmosphere.
  • The greenhouse gases are being emitted by different sources:
02_figure_SPM_2 (1)
Credit: IPCC AR5 Working Group 3 Graphics

Greenhouse Gases: Sources and Atmospheric Lifetime

Carbon Di Oxide (CO2) is the most emitted green house gas worldwide. The sources of CO2 are the burning of fossil fuels such as coal, petrol, diesel and natural gas in transportation, during electricity production, cement manufacturing and other goods.

Forests are major sink of CO2. When forests are degraded huge amount of CO2 gets released into the atmosphere which otherwise would get absorbed by the forests. The degradation of forests is also one of the reasons of increase in the CO2 concentration.

The atmospheric lifetime of CO2 is 5-200 years. The atmospheric lifetime is the approximate time a green house gas takes to return to its original concentration in the atmosphere. It happens via the conversion of the gas into some other chemical compound or via a sink.

Methane One of the major sources of methane emission is the rice fields and wetlands.The cattle such as cow, buffalo, sheep, goat release a lot of methane during the digestion process.

Land filling sites are also a major source of methane gas. In such places microbes are present. These microbes in the absence of sufficient amount of oxygen degrade the organic waste to make their food. In this process methane gets emitted.The atmospheric lifetime of methane is 12 years.

Nitrous Oxide The main source of nitrous oxide is industrial processes and fertilizers. Natural processes in soils and oceans also release N2 The atmospheric lifetime of nitrous oxide is 114 years.

Chlorofluorocarbon These are used in refrigeration equipments, air conditioning systems and as propellant in aerosol sprays. Most of the CFC gets released in the environment through the leakage in the storage system or via the aerosol. The atmospheric life time of chlorofluorocarbons vary from 55 years to 140 years.

The Warming Potential of Greenhouse Gases

The capability to trap heat is different in different gases. A gas with more heat trapping ability has more warming potential.

For all the greenhouse gases this is expressed in relation to the warming potential of CO2.

The CO2 is the reference point not because it is the most potent (which it is not) but because it is causing the maximum warming owing to much higher concentration in the atmosphere than the other gases.

Percentage Proportion of Different Greenhouse Gases Photo Credit: IPCC 2014
  • A molecule of methane has the potential to cause 20 times more warming than a molecule of CO2. Nitrous oxide causes 300 times more warming while the chlorofluorocarbons trap thousands of times more heat than CO2 and thereby its global warming potential is much more.
  • This means that a gas like methane although has short atmospheric life time but it is able to exert its warming effect more efficiently than COwhile the excess of nitrous oxide is dangerous in terms of both the atmospheric lifetime as well as potential.
  • The cumulative effect of all green house gases towards global warming is expressed in terms of equivalent amount of CO2. For example since 1990 about 6 billion metric tons of carbon dioxide equivalent have been emitted worldwide.
  • A scientific intergovernmental body called “Intergovernmental Panel on Climate Change’ (IPCC) has been working since 1988 under the auspices of United Nations. IPCC consists of a large group of scientists from around the world who review the latest scientific findings and reach to a consensus with regard to global warming. IPCC publishes reports covering scientific, technical and socio economically relevant information to increase the understanding about the scientific basis of climate change caused by humans.
  • As per the IPCC report published in 2007, the dominant cause of global warming over the last 50 years is the greenhouse gas forcing. The effect of greenhouse gases towards warming would have been even more but some of the warming gets offset by the cooling effect of volcanic and anthropogenic aerosols.

One Comment

  • Michael Koop

    Mankind is contributing virtually nothing towards global warming. Anybody who studies the history of this
    planet/galaxy over the past several million years will realize global warming is simply a cycle that has repeated
    itself over history as well as repeated ice ages. Fly over the planet in an airplane & you will see dense forests
    and vacant land everywhere.

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