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 argue 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 Holocene and the upper part of the last Glacial, and present two possible mechanisms (involving the role of solar UV variations and solar wind/cosmic rays) that may explain how small variations in solar activity are amplified to cause significant climate changes. Accepting the idea of solar forcing of Holocene and Glacial climatic shifts has major implications for our view of present and future climate. It implies that the climate system is far more sensitive to small variations in solar activity than generally believed. (C) 1999 Elsevier Science Ltd. All rights reserved.