Global Warming in the Past

Global warming is an issue of major concern these days, which is why scientists are studying the climate of the late Cretaceous period.  The late Cretaceous period is an era of natural history that began 100 million years ago and ended 65 million years ago with the extinction of the dinosaurs.  Although temperatures in the early Cretaceous period were mild with ice covering much of the earth, there is substantial evidence that the late Cretaceous period was marked by greenhouse conditions and an unusually warm climate. 

Isotopic data recovered from late Cretaceous period sediments reveals temperatures between 20 and 28 degrees Celsius in arctic regions.  This suggests that the global average temperature was at least 10 degrees higher than it is today.  Additional evidence of global warming is given by repeated deposition of Black Shale into the oceans, altered current patterns, and increased marine productivity.  Black Shale deposits indicate an increased rate of erosion, suggesting a rise in ocean levels.  This led to increased deposits of nutrients in the seas and elevated marine productivity. 

A study of diatomic remains encased within late Cretaceous layer sediments also shows that, unlike the early Cretaceous climate, late Cretaceous summers were free of ice.  The size distribution of clay and sand grains within the remains indicated that winters were not cold enough to support the formation of thick glacial ice.   

Further indication of warming is also given by the recent discovery in the Canadian Arctic of fossils of certain species of turtles known to remain in tropical regions.  Turtles are cold-blooded and non-migratory, so they are often used to determine climatic conditions.  The species discovered were known to adhere to regions with a warm-month temperature mean of 17.5 degrees Celsius, for which the typical corresponding mean annual temperature is 2.5 degrees Celsius.  This discovery demonstrates that temperatures in the late Cretaceous period were at a global maximum.

This sudden global temperature spike is attributed to a rise in volcanic activity, which is evidenced by carbon isotope deposits in Cretaceous layer sediments.  During the late Cretaceous period, sea-floor spreading increased giving rise to Large Igneous Provinces like the Ontong Java Plateau, the Kerguelen Plateau, and the Rio Grande Rise.  Volcanic activity on these newly emerged land masses released high amounts of carbon dioxide and other greenhouse gases into the atmosphere and led to global warming.

By analyzing the environmental and biological responses to the climate changes of the late Cretaceous period, scientists hope to learn more about the effects of global warming and the best ways for people to prepare themselves.  They also aim to answer questions about what kinds of creatures would survive the longest and to address concerns about how to maintain environmental stability in the face of global warming.