The Climate of the Last Millennium

9,38

MB

45

stron

2380

ID

University of Massachusetts

2002

rok

Introduction

We are living in unusual times. Twentieth century climate was dominated by near universal warming

with almost all parts of the globe experiencing temperatures at the end of the century that were

significantly higher than when it began (Figure 6.1) (Parker et al. 1994; Jones et al. 1999). However

the instrumental data provide only a limited temporal perspective on present climate. How unusual

was the last century when placed in the longer-term context of climate in the centuries and millennia

leading up to the 20th century? Such a perspective encompasses the period before large-scale

contamination of the global atmosphere by human activities and global-scale changes in land-

surface conditions.

By studying the records of climate variability and forcing mechanisms in the recent past, it is

possible to establish how the climate system varied under “natural” conditions, before anthropogenic

forcing became significant. Natural forcing mechanisms will continue to operate in the 21st

century, and will play a role in future climate variations, so regardless of how anthropogenic effects

develop it is essential to understand the underlying background record of forcing and climate

system response.