The Mesozoic

There is an agreement that during this period the Earth was exhibiting only little seasonal changes, and the temperature differences between equator and poles were relatively small. This period is the age of dinosaurs, and the average temperature was fairly warm.

Toward the end of the Jurassic and the beginning of the Cretaceous period, some indications of renewed glaciation have been found, such as ice-rafted debris in Arctic regions as well as a reduction in sea level around 126 million years. Tree-ring studies of fossilized trees show that the growth during winters slowed down, hence there was a transitional period of cooler and more seasonal climate.

The mid-Cretaceous period at about 100 million years was probably the warmest period in the Earth’s history. Reasonable data suggest that the average temperature was 6-12ºC warmer than now (0-5ºC in the tropics, 35ºC in the Arctic and Antarctic). A major factor in this even distribution of temperature was the distribution of landmasses. There was no continental mass blocking flow around the equator, and circumpolar airflows (“jet stream”) were missing.

The polar temperatures may have been as high as 17ºC (65ºF). Hence there was no icecap, and also now significant cooling of ocean currents. The cooling of ocean currents in the polar regions pulls the colder water down wards, thus propelling the current. These currents were much weaker than today.

There is still much debate on the actual global temperature distribution and its effects on Climate. This period is often used as a comparison to modern global warming.

The Mesozoic era ends with a brief cooling, accompanied by the extinction of dinosaurs.