Climate Variability and It’s Causes

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Climate Variability

The temporal changes in weather phenomena, which is part of general circulation of atmosphere and occurs on a yearly basis on a global scale. Climate change and climate variability are the concern of human kind in recent decades all over the world.

The recurrent drought and desertification seriously threaten the livelihood of over 1–2 billion people who depend on the land for most of their needs. The weather related disasters viz. drought and floods, ice storms, dust storms, land slides, thunder clouds associated with lightening and forest fires are uncommon over one or other region of the world. The year 1998 was one of the recent weather related disaster year, which caused hurricane house in Central America and floods in China, India and Bangladesh. Canada and New England in the U.S. suffered heavily due to ice storm in January while Turkey, Argentina and Paraguay with floods in June 1998. Vast fires in Siberia burned over three million acres of forests. Human and crop losses are the worst phenomena in such weather disasters, affecting global economy to a considerable extent. In 2004, nobody can forget the Tsunami problem in Indonesia, India, Sri Lanka and other Asian countries.

The 1997-98 El-Nino events, the strongest of the last century is estimated to have affected 110 million people and cost the global economy nearly US $ 100 billion. Statistics compiled from insurance companies for the period 1950-1999 show that major natural catastrophes that are mainly weather and climate related caused estimated economic losses of US $ 960 billion. Most of the losses were recorded in recent decades. Increase in aerosols due to emission of green house gases including black carbon and chlorofluorocarbons (CFCS), ozone depletion, UV-B filtered radiation, cold and heat waves, global cooling and warming and “human hand” in the form of deforestation and loss of wetlands in the process of imbalanced development for betterment of human kind may be caused factors for climate variability and climate change.

Causes of Climatic Variability

External causes

• Solar output: An increase in solar output by 0.3% when compared to 1650–1700 A.D. data.

• Orbital variation:

1. Earth orbit varies form almost a complete circle to marked ellipse (Eccentricity).

2. Wobble of earth’s axis (Precession of equinox)

3. Tilt of the earth’s axis of rotation relative to the plane of the orbit varies between 21.8º and 24.4º.

Internal causes

• Changes in the atmospheric composition-change in the green house gases especially CO2

• Land surface changes particularly the afforestation and deforestation

• The internal dynamics of southern oscillation–changes in the sea surface temperature in western Tropical Pacific (El-Nino/La-Nina) coupled with Southern Oscillation Index, the Tahiti minus Darwin normalized pressure index leading to the ENSO phenomena

• Anthropogenic causes of climate variation in green house gases and aerosols.


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