Historical Climate Changes In India
We have clear evidence that past Indian environments experienced very different regional climates. Fifty million years ago, most of the Indian peninsula was equable, warm and humid. Humid rain forests thrived in the Deccan during this period. Areas of Rajasthan which today are very dry, were humid and supported a lush flora. In the Late Tertiary, India experienced desiccation and further warming in the north, west and Deccan. This probably can be linked to the closing of the Tethys Sea and the loss of its influence on weather patterns. But at this time, along the south-eastern coast of the Peninsula, humid forest continued to dominate, much like the flora that occurs in the Western Ghats today.
The Pleistocene period probably showed cyclical warm-humid and cold-dry periods that typified this period in Eurasia. More recently, during the time of human occupation, we see continuing changes in the climate. Two thousand years ago the Indian north-west was again humid, with tropical forests containing evergreen trees of Indo-Malayan affinities. There is also indication that in the period 100 B.C.-100 A.D. conditions were more humid that they are today in many parts of northern India.
Today, massive ice caps and upland glaciers sit atop the high Himalayas. Seasonally torrid conditions exist in the interior of the Peninsula and Indo-Gangetic Plain. Much of Ladakh and Tibet are cold and dry. Areas in the Western Ghats, coastal Bangladesh, the Assam hills, and Arunachal Pradesh are perennially wet. This broad range of physical conditions promotes physiognomic and floristic differences in present-day Indian plant communities.