katglobalcooling

Millions of years ago, the earth was quite different from its current state. The earth was a warm climate, believed to be warmer than today’s climate and the thermal contrasts between the poles and equator were low during the Phanerozoic, which translates into stable uniform warmth (Newton, 1989). If the earth is warm and organisms are used to the warmth, what happens when things get cooler? Well, there is a simple logical connection: if temperatures drop quickly, then animals cannot adjust and they die. Organisms used to a warm tropical climate would die. The same logical relation is true when temperatures rise: organisms used to cooler temperatures will suffer as a result of the increased heat.

Glaciation, a common cause of global cooling, is linked to the Late Ordovician, Late Permian, and Late Devonian extinctions. For more information on global cooling, click here to link to Becky’s page.

The links found between global cooling and mass extinction are as follows: widespread extinction of tropical faunas, disappearance of reefs which thrive in warmer waters, migration of warm climate taxa closer to the equator, continental glaciation, and low ?18O isotope records demonstrate that cooling was taking place during the times of the mass extinctions (Brenchley, 1998).

Newton illustrates the link between global cooling and its effects on life with a mini model concerning a regional extinction during the Plio-Pleistocene that took place approximately three million years ago. At that time, Northern Hemisphere glaciation led to changes in the currents and brought about the cold Labrador Current southward along Eastern North America. This resulted in the elimination of about 1,000 mulluscan species and over 40% mulluscan species went extinct in the Mediterranean region. This shows that cooler waters introduced to warm tropical regions can result in extinction (Newton, 1989). More evidence that global cooling has adverse effects: the evergreen example as stated earlier regarding the bolide impact and cooling.

Volcanism was also a factor in causing rapid climate change. Volcanoes have extremely acid rich eruptions that result in the expulsion of volcanic ash, carbon dioxide, and sulfuric gases into the stratosphere. These form aerosols which absorb and scatter sunlight, leading to global cooling (Ward, 1989). Carbon dioxide is also linked to the greenhouse effect, which causes temperatures to rise. For more on volcanism, click here. There is evidence of volcanism taking place in the Late Cretaceous and Late Triassic.

The formation of new super-continents is also thought to be a factor in mass extinctions. The formation of a massive super-continent Gondowanaland around 245 million years ago coincides with Late Permian mass extinction. This causes major temperature fluctuations that constitute rapid climate changes. When the super-continent formed, the interior of the continent grew hotter in the summer and colder in the winter because it was too big to be cooled or warmed by maritime influences (Ward, 1989). It is estimated that the summer highs exceeded 100°F but there was a freezing dry cold during the nights (Ward, 1989). Some areas might also become isolated and have less rainfall and suffer from desertification. This would affect organisms that were not adjusted to warmer or cooler temperatures and lower rainfall.