Middle Pliocene Warm Period

The Middle Pliocene Warm Period (mPWP), also known as the Mid-Piacenzian Warm Period or the Pliocene Thermal Maximum, was an interval of warm climate during the Pliocene epoch that lasted from 3.3 to 3.0 million years ago (Ma).

Climate
The global average temperature in the mid-Pliocene was 2–3 °C higher than today, global sea level 25 meters higher, and the Northern Hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 Ma. Global precipitation was marginally increased by 0.09 mm/yr according to CCSM4 simulations. As during the Quaternary glaciation, glacial-interglacial cycles existed during the mPWP and it was not a uniform and stable climatic interval.

Carbon dioxide concentration during the Middle Pliocene has been estimated at around 400 ppmv from 13C/12C ratio in organic marine matter and stomatal density of fossilised leaves, although lower estimates of between 330 and 394 ppm over the course of the whole mPWP and 391 ppm in the KM5c interglacial, during the warmest phase of the mPWP, have been given.

Comparison with present global warming
The mPWP is considered a potential analogue of future climate. The intensity of the sunlight reaching the Earth, the global geography, and carbon dioxide concentrations were similar to present. Furthermore, many mid-Pliocene species are extant, helping calibrate paleotemperature proxies. Model simulations of mid-Pliocene climate produce warmer conditions at middle and high latitudes, as much as 10–20 °C warmer than today above 70°N. They also indicate little temperature variation in the tropics. Model-based biomes are generally consistent with Pliocene palaeobotanical data indicating a northward shift of the tundra and taiga and an expansion of savanna and warm-temperate forest in Africa and Australia. The increased intensity of tropical cyclones during the mPWP has been cited as evidence that intensification of such storms will occur as anthropogenic global warming continues.