Introduction

Transfer, storage and release of carbon (C) between the atmosphere and terrestrial and oceanic sinks typically occur over several different time scales. These processes are strongly dependent upon, and can potentially influence, the global climate. Part I is intended to provide a large-scale, long-term perspective on the role of forest ecosystems in the C cycle. The Working Group summary paper reports the group analysis of the extent to which climate variation over various time scales have influenced global terrestrial contributions to changes in the atmospheric C record. The individual articles review past changes in terrestrial C pools as determined from the observational record. They examine changes in the geologic past (e.g., due to long term shifts in climate), in the recent historical past (including the contributions of landuse change and deforestation) and contemporary 20th century trends (considering, for example, the effects of post-industrial pollution and large-scale tropical deforestation). Some Chapters also review current projections of ecosystem C dynamics into the foreseeable future.