Global Warming: Effects and Causes
Global Warming is the increase in Earth's mean surface temperature because of the effect of greenhouse gases. These gases absorb longwave radiations and warm the atmosphere, and this process is called a Greenhouse effect.
It had led to many changes on the planet, such as a rise in sea level; massive melting of snow and land ice, elevated heat content of the oceans, increased humidity, change in the timings of seasonal events, and many others.
For both land and ocean, the global mean surface temperature indicates warming of 0.85°C from 1880 to 2012. During the period 1906-2005, the Earth’s mean surface temperature had increased by 0.74±0.18°C. Hence, it is seen that the rate of warming approximately doubled for the last half of that duration (0.13±0.03°C per decade, as compared to 0.07±0.02°C per decade).
Effects of Greenhouse Gases (GHGs) on Global Warming
The main greenhouse gases, namely: Carbon dioxide (CO2); Methane (CH4); Nitrous oxide (N2O); Hydrofluorocarbons (HFCs); Perfluorocarbons (PFCs); and Sulphur hexafluoride (SF6). The impact of any GHG is based on the magnitude of the rise in its concentration, its duration in the atmosphere and the wavelength of radiation that is absorbed.
1. Carbon dioxide is the GHG which is present in the largest concentration in the atmosphere. Its emission chiefly comes from fossil fuel combustion. It is showing a rise of about 0.5% per annum.
2. Chlorofluorocarbons (CFCs) are produced due to anthropogenic activity. Ozone is present in the stratosphere where ultraviolet (UV) radiations convert oxygen into ozone. Hence, the UV rays do not reach the Earth’s surface. The CFCs which goes into the stratosphere destroys the ozone, which is evidently seen over Antarctica. The reduction of ozone concentration in the stratosphere is known as the ozone hole. This permits the UV rays to pass through the troposphere.
3. Nitrous oxide is naturally produced by oceans and rainforests. Man-made sources of nitrous oxide include nylon and nitric acid production, the use of fertilisers in agriculture, cars with catalytic converters and the burning of organic matter.
4. Hydrofluorocarbons (HFCs) are used as refrigerants, especially after the ozone-destroying CFCs had been under the Montreal Protocol.
5. Perfluorocarbons (PFCs): Emitted as a result of production of flourites, they have an atmospheric lifetime of more than 1,000 years.
6. Sulphur hexafluoride (SF6): The most powerful greenhouse gas yet discovered, it is emitted as result of production of flourites.
Global efforts have been started for decreasing the emission of GHGs into the atmosphere. Of the many initiatives, the most important one is the Kyoto protocol declared in 1997, and came into effect in 2005, authorized by 141 countries. Kyoto protocol controlled 35 industrialised nations to reduce the emission of GHGs by the year 2012 to 5% less than the levels present in the year 1990.
The concentrations of greenhouse gases are not larger than oxygen and nitrogen, because neither has more than two atoms per molecule, and so they lack the internal vibrational modes that molecules with more than two atoms possess. Both water and CO2 have these "internal vibrational modes", and these modes of vibrations can consume and resend infrared radiation, which causes the greenhouse effect.
Impacts of Global Warming
1. Rising Sea level: Flooding of fresh water marshlands, low-lying cities, and islands with marine water is one of the major effects of global warming.
2. Changes in rainfall patterns: In some areas, droughts and fires happen, whereas in other areas, flooding takes place. This all is due to changes in rainfall pattern.
3. Melting of the ice peaks: Due to melting of the ice peaks, there is loss of habitat near the poles. Now the polar bears are considered to be greatly endangered by the shortening of their feeding season because of declining ice packs.
4. Melting glaciers: There is a significant melting of old glaciers.
5. Spread of disease: There is spread of diseases like malaria due to migration to newer and currently warmer regions.
6. Thinning of Coral Reefs due to warming seas as well as acidification because of carbonic acid formation: Almost one-third of coral reefs are now severely damaged by warming seas.
7. Loss of Plankton owing to warming seas: The large (900 miles long) Aleutian island ecosystems consisting of whales, sea lions, sea urchins, kelp beds, fish, and other aquatic animals, has now reduced due to loss of plankton.