Cold Climates

During the last great Ice Age, about 18,000 years ago, the Earth’s climate was radically different from that of today. The difference was larger even than is sometimes projected for future climate states under doubled CO₂. Studies of bubbles in polar ice cores have shown that Ice Age atmospheric CO₂ was much lower than recent pre-industrial levels, which supports a link between CO₂ and climate.

Studies of the geo-chemical composition of sea floor fossils have shown that the circulation patterns of the ocean during the last glacial maximum may have been quite different from those in the modern ocean. Both theory and these observations strongly support the idea that changes in ocean chemistry and circulation can act to alter atmospheric CO₂, and the complete climate state. Furthermore, there is evidence that 11,000 years ago, the ocean circulation may have switched back abruptly to a state much closer to that of the Ice Age ocean - returning much of the world to glacial conditions. This switch appears to have occurred over a period of less than 300 years. It is thus important to consider the possibility that future ocean circulation could change drastically on the decadal-to-centuries time scale relevant to our immediate future. The potential for rapid switches in the mode of ocean circulation has obvious implications for carbon uptake by the ocean and climate change.

The linkage between ocean circulation and abrupt climate change can be illustrated by data sets from piston core MD95-2036, the longest piston core from the Atlantic ocean collected by Ed Boyle's group during the IMAGES 1 coring expedition:

The figure shows abrupt changes in deep ocean sedimentation and chemical properties during the previous interglacial period, 118,000-127,000 years ago.