“Global climate changes have been far more intense (12 to 20 times as intense in some cases) than the global warming of the past century, and they took place in as little as 20–100 years. Global warming of the past century (0.8° C) is virtually insignificant when compared to the magnitude of at least 10 global climate changes in the past 15,000 years. None of these sudden global climate changes could possibly have been caused by human CO2 input to the atmosphere because they all took place long before anthropogenic CO2 emissions began. The cause of the ten earlier ‘natural’ climate changes was most likely the same as the cause of global warming from 1977 to 1998.”
Professor Don Easterbrook
Ref: Alley, R.B 2000 The Younger Dryas cold interval as viewed from central Greenland. Quaternary Science Reviews 19: pp 213-226.