Don Bogard, isotopic and nuclear geochemistry: Today, when many are concerned about the Earth possibly over-heating through greenhouse warming, it is worthwhile to look into the not very distant past when the Earth over-cooled. Most people have heard of the Ice Age but probably know very little about it. Some may remember climate scientists in the 1970s expressing concern that Earth may be entering a new ice age, because of growing evidence that Earth was cooling (in spite of growing atmospheric carbon dioxide of CO2). What was the ice age, why did it occur, and is it now in our past, or also in our future?
Dennis Avery is an agricultural and environmental economist and a senior fellow for the Center for Global Food Issues: In a recent New York Times column, Nicholas Kristof misleads us about the awful history of Easter Island (2,300 miles west of Chile), whose vegetation disappeared in the cold drought of the Little Ice Age. In doing so, he blinds modern society to the abrupt, icy climate challenge that lies in our own future.
John Robson: For the past 2.5 million years the Earth has been unusually cold, with repeated glaciations whose periodic advances and retreats science cannot model or predict. In fact we are still in an “ice age” today, with significant polar ice, though in a relatively warmer “interglacial”. Fortunately. Civilization would be impossible without the warming that started suddenly 12,000 years ago, and would become very difficult if the glaciers began another sudden advance. If the Earth actually is now warming, relative to 15,000 years ago or indeed the “Little Ice Age” from the end of the Middle Ages into the mid-19th century, it would be neither surprising nor man-made.
Euan Mearns, geologist: He takes a close look at the data on temperatures, carbon dioxide (CO2), and methane (CH4) found in the Vostok Ice Core of Antarctica. He focuses on the Eemian warm period between 130,000 and 115,000 years ago. This warm period was the last warm period before the current warm period, the Holocene. In her 2008 graphs showing the relationship between CO2 and temperatures from the Vostok Ice Core covering the entire record, Jo Nova stated the average lag was about 800 years, with temperatures rising (falling) about 800 years before CO2 rising (falling). This lag indicates that CO2 could not be the cause of rise or fall of temperatures.