Solar radiation, temperature, pressure, winds, humidity and precipitation exhibit spatial and seasonal variations. These are the major elements of climate. The most important factor affecting the climate is the latitude. Latitude determines the amount of isolation received from the sun, and the main temperature zones and major pressure and wind belts are also related to latitude. The modes of life of tribal people are also directly related to the climate conditions. Forests are fast vanishing from our country. Extensive and unabated deforestration, over-grazing and the growing hunger for land has hit the ecology of the country so badly.
Throughout earth history, the climate has changed globally and locally throughout all periods of time. Climate change has many natural as well as man-made causes. More important natural causes are enumerated below:
1. Variation in the amount of solar radiation: Since the sun was born, its radiation burst is increasing steadily. In addition to that it shows a periodic variation over a 10-15 year period. This is exemplified by variation in the number of sunspots.
2. The position of Earth relative to Sun and position of continents relative to the equator: Earth’s orbit around the Sun changes from a more circular to a more elliptical one over a cycle of 90000 to 100000 years. So, the amount of yearly solar radiation that Earth receives varies less when it is more circular, than when it is more elliptical. This has profound effect on global climate.
Wobbling of Earth on its own axis is another determining factor that governs the extent of solar radiation received by Earth.
Earth’s seasons are caused by the 23.5° angle of its axis of rotation. As Earth orbits the sun, the tilt of the planet’s axis changes throughout the year and this change is different for different zones with respect to the equator. This phenomenon controls the extent of radiation reaching different regions of Earth.
Smaller natural factors that are important over shorter period of time are volcanic eruptions, asteroid impacts and ocean-atmosphere interactions.
Human activities like burning fossil fuel and biomass increase greenhouse gas levels in the atmosphere. Addition of greenhouse gases coupled with concomitant deforestation causes the atmosphere to heat up at a disproportionate rate, culminating in rapid climate change.
There are other human causes such as land use changes due to urbanisation and air pollution (especially fine particulate pllution) that too catalyze global climate change in a profound way.