Global warming: a previous very warm period (Introduction)

by David Turell , Saturday, August 31, 2019, 18:30 (1912 days ago) @ David Turell

The Earth was 2-3 degrees warmer than now, and sea levels were very high due to melted ice caps:

https://phys.org/news/2019-08-scientists-evidence-high-level-sea.html

"An international team of scientists, studying evidence preserved in speleothems in a coastal cave, illustrate that more than three million years ago—a time in which the Earth was two to three degrees Celsius warmer than the pre-industrial era—sea level was as much as 16 meters higher than the present day. Their findings represent significant implications for understanding and predicting the pace of current-day sea level rise amid a warming climate.

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"The project focused on cave deposits known as phreatic overgrowths on speleothems. The deposits form in coastal caves at the interface between brackish water and cave air each time the ancient caves were flooded by rising sea levels. In Artà Cave, which is located within 100 meters of the coast, the water table is—and was in the past—coincident with sea level, says Professor Joan J. Fornós of Universitat de les Illes Balears.

"The scientists discovered, analyzed, and interpreted six of the geologic formations found at elevations of 22.5 to 32 meters above present sea level. Careful sampling and laboratory analyses of 70 samples resulted in ages ranging from 4.4 to 3.3 million years old BP (Before Present), indicating that the cave deposits formed during the Pliocene epoch. The ages were determined using uranium-lead radiometric dating in UNM's Radiogenic Isotope Laboratory.

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"'Sea level changes at Artà Cave can be caused by the melting and growing of ice sheets or by uplift or subsidence of the island itself," said Columbia University Assistant Professor Jacky Austermann, a member of the research team. She used numerical and statistical models to carefully analyze how much uplift or subsidence might have happened since the Pliocene and subtracted this from the elevation of the formations they investigated.

"One key interval of particular interest during the Pliocene is the mid Piacenzian Warm Period—some 3.264 to 3.025 million years ago—when temperatures were 2 to 3º Celsius higher than pre-industrial levels. "The interval also marks the last time the Earth's atmospheric CO2 was as high as today, providing important clues about what the future holds in the face of current anthropogenic warming," Onac says.

"This study found that during this period, global mean sea level was as high as 16.2 meters (with an uncertainty range of 5.6 to 19.2 meters) above present. This means that even if atmospheric CO2 stabilizes around current levels, the global mean sea level would still likely rise at least that high, if not higher, the scientists concluded. In fact, it is likely to rise higher because of the increase in the volume of the oceans due to rising temperature.

"'Considering the present-day melt patterns, this extent of sea level rise would most likely be caused by a collapse of both Greenland and the West Antarctic ice sheets," Dumitru said."

Comment: It is of great interest that hominins were evolving during this period. They survived and we should survive this current warming .