EARTH × CLIMATE

A Plateau Makes a Monsoon

~40 to 10 million years ago

Phanerozoic · Cenozoic · Paleogene · Eocene

India drove into Asia and raised a plateau the size of western Europe five kilometres above the sea. In summer that surface heats far faster than the ocean beside it, and the air lifting off the plateau draws wet ocean air inland behind it. Half the world's people now live under the rain that arrives that way.

Why it matters

This is the textbook case of tectonics writing a climate, and it is still not proven. The sequence can be followed step by step: three pulses of uplift, a wind system that strengthened, and fresh rock laid bare that may have pulled carbon dioxide from the air as it weathered and cooled the planet. What the evidence cannot yet say is whether the plateau made the monsoon or sharpened one that already blew.

Dating & uncertainty

Three pulses of uplift are read from the rocks, around 40 to 35, 25 to 20 and 15 to 10 million years ago. Only the middle one has good climate evidence beside it: the oldest cannot be tested for want of data, and the youngest falls in a spell of global cooling and Antarctic glaciation that could have moved the monsoon by itself. No rock records the birth of a wind system, so which pulse started the monsoon, and how much the plateau counts against falling carbon dioxide, come out of climate models rather than out of the ground.

Sources

1. Tada et al. (2016), Progress in Earth and Planetary Science · Evolution and variability of the Asian monsoon and its potential linkage with uplift of the Himalaya and Tibetan Plateau
2. Fu et al. (2022), CATENA · Tectonic and climatic forcing of chemical weathering intensity in the northeastern Tibetan Plateau since the middle Miocene
3. Hutchinson et al. (2021), Climate of the Past · The Eocene-Oligocene transition: a review of proxy data, models and comparisons

Earth history as one day

23:47:1812 min 41 s before midnight

if Earth’s 4.54 billion years were compressed into a single day