Australia: The Land Where Time Began

A biography of the Australian continent 

Miocene Climate

At the close of the Oligocene, about 25 Ma, the climate changed rapidly again, the temperatures again rising rapidly. This sudden rise of global temperatures saw the retreat of the Antarctic ice sheets and the rapid rise of sea levels. At the start of the Miocene, the first epoch of the Neogene Period, a bit less than 24 Ma there was a brief period of cooling, the Mi-1, during which there was expansion of the ice sheets on Antarctica and a sudden sea level drop. Warmer, more humid conditions soon returned, persisting for the first half of the Miocene Epoch. At this time coniferous forests returned to areas they had previously been displaced from by tundra. During the Mid-Miocene Climate Optimum (MMCO), the last time the atmospheric CO2 levels rose above those of the present, 17-15 Ma, temperatures were 3-6° C higher than the present. According to Aradhna Tripati et al. of UCLA, atmospheric CO2 levels were at about 400-450 ppm at that time, around the levels they are expected to reach in the next decade if emissions are not cut drastically very soon. It is expected that atmospheric carbon dioxide levels will need to rise only slightly higher than their present levels to eventually lead to a rise of 3-6° C above the pre-industrial levels, assuming the link between atmospheric carbon dioxide levels and temperature is the same now as it was in the MMCO, obviously higher than the 2° C that is widely believed to be the point that must not be exceeded by keeping the CO2 levels no higher than 450 ppm. According to the author these higher levels of the global average temperatures would almost certainly result in double-digit temperature rises at high latitudes with the wholesale melting of the ice sheets of Greenland and West Antarctica. Tripati et al. has observed that there were no floating ice shelves in the Antarctic and little land ice in the Arctic during the MMCO. According to the author¹ in East Antarctica neither sea ice of large permanent sheets formed before the CO2 levels dropped below 350-400 ppm in the rapid cooling period with the expansion of glaciers after the MMCO, with large ice sheets forming on Greenland and West Antarctica only when the atmospheric levels dropped below 300 ppm.

The Author suggests that MMCO appears to be telling us that atmospheric levels slightly higher than those of the present that are almost certain to be reached in a few decades, will result in a global average temperature rise to near the top of the range that has been projected in the IPCC's Fourth Assessment report, assuming the excessive levels of CO2 are maintained for long enough. If this does occur the author¹ suggests there will most probably be wholesale melting of the polar ice that will eventually push sea levels to levels reached in the MMCO, 25-40 m above those of the present. About 14 Ma there was a sudden cooling, the global average temperature dropping 6-7° C with a significant buildup of ice at both poles. A bit over 5 Ma, near the close of the Miocene Epoch ice covered Greenland and Antarctica, the transition to icehouse conditions was under way in spite of warm interglacials.

Sources & Further reading

  1. McGuire, Prof. Bill, 2012, Waking the Giant: How a changing climate triggers earthquakes, tsunamis, and volcanoes, Oxford University Press.

 

Author: M. H. Monroe
Email:  admin@austhrutime.com
Last updated 25/08/2012

Cenozoic Climate
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading