The role of solar forcing upon climate change

Evidence for millennial-scale climate changes during the last 60,000 years has been found in Greenland ice cores and North Atlantic ocean cores. Until now, the cause of these climate changes remained a matter of debate. We ar gue that variations in solar activity may have played a significant role in forcing these climate changes. We review the coincidence of variations in cosmogenic isotopes (C-14 and Be-10) with climate changes during the Holoce ne and the upper part of the last Glacial, and present two possible mechani sms (involving the role of solar UV variations and solar wind/cosmic rays) that may explain how small variations in solar activity are amplified to ca use significant climate changes. Accepting the idea of solar forcing of Hol ocene and Glacial climatic shifts has major implications for our view of pr esent and future climate. It implies that the climate system is far more se nsitive to small variations in solar activity than generally believed. (C) 1999 Elsevier Science Ltd. All rights reserved.