What factors most account for the creation of a tropical climate throughout much of the Indian subcontinent?

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Arrowheads indicate estimated change points. Increase of MDE between 45 and 40 Ma points to a complete terrestrial connection between colliding continents. Periods of stagnant MDE coincide with intensification of the monsoon system and increased seasonality, whereas the strong decrease in MDE after the Mid Miocene Climatic Optimum might be elicited by increasing aridity in northern India.