PAGES — Past Global Changes and their Significance for the future: an Introduction

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Introduction

The dominant theme of the present collection of articles is past climatic and environmental change. The aim is to present a range of research topics within the broad, interdisciplinary field defined by the major goals of the IGBP Past Global Changes (PAGES) project. The over-riding concern of the PAGES project is to provide a quantitative understanding of the Earth's environment in the geologically recent past and to define the envelope of natural environmental variability, against and alongside which anthropogenic impacts on the Earth System may be assessed. Within this almost boundless remit, focus has been achieved by concentrating on those aspects of past environmental change that most affect our ability to understand, predict and respond to future changes.

PAGES therefore, works to identify and elucidate those aspects of past global change that are of great significance to human societies. It seeks to promote and co-ordinate research that extends knowledge of our changing environment beyond the short, recent period for which we have instrumental records and to understand the dynamics of climate and environmental change as recorded in high-resolution, chronologically controlled, multiproxy records of the Earth's past.

The papers gathered together here are part of the outcome of the first PAGES Open Science Meeting held in the Senate House, University of London, April 19–23, 1998. The meeting, on “Past global changes and their significance for the future”, took the form of a sequence of invited overview papers by some 30 experts drawn from all over the world, interspersed with several hundred posters illustrating the best current scientific research in the field. A volume of abstracts covering the full range of presentations is available from the PAGES International Project Office.

In bringing together the majority of the oral contributions at the meeting, the present volume spans a wide range of paleoscience. The papers encompass only a small portion of the diversity of PAGES activities and of the archives and research tools upon which PAGES research draws. Our hope is that they provide a range of examples which highlight the possibilities, given quantitative calibration and robust chronology, for local, regional and global paleoenvironmental reconstruction from proxy archives. A review of PAGES programs is contained in the PAGES Status Report and Implementation Plan (IGBP Report 45:ISSN 0284-8015) and is regularly updated on the PAGES website (http://www.pages.unibe.ch).

Section snippets

Paleoenvironmental archives and methods

The first section of papers comprises a series of reviews which highlight individual paleoenvironmental archives. Each type of archive provides a valuable record, with unique strengths and weaknesses. Brought together, compared and contrasted, they can provide the basis of a reconstruction worth far more than the sum of the parts.

One of the most compelling and, by now well known, lines of evidence in support of the proposition that increased concentrations of greenhouse gases in the atmosphere

The pole–equator–pole transects

The fact that past climate change has shown both global coherence as well as highly differentiated regional expression, implies that any reconstruction of past global change must be placed within a robust, spatial framework. A major step in this direction has been the establishment, by PAGES, of the pole–equator–pole (PEP) transects (Fig. 1). Each transect presents unique challenges and opportunities.

The vast latitudinal span of the American continent provides the PEP I transect with a wealth

Stadial/Interstadial transitions

Over the last 60,000 yr the global climate has undergone major millennial scale oscillations. Until 11,000 yr ago, these flips, which took place every few thousand years, were so sudden and so dramatic that they changed the climate of Northern Europe between temperate and glacial conditions often within a century or less, and their impact was felt right across the Northern hemisphere. Indeed the rate of change in Greenland at the onset of the Holocene, shown in the first paper of this section by

Paleoclimate modeling and data-model comparison

Convection in the northern North Atlantic, the driving force behind the thermohaline circulation, is highly sensitive to sea surface conditions. Manabe and Stouffer, show how meltwater pulses can force an oceanic general circulation model to undergo a Younger Dryas cooling in the North Atlantic region due to a shut down of thermohaline circulation. Depending on the level of fresh water input, their modeled thermohaline circulation can rebound or remain in a stable quiescent mode. In the

Holocene environmental changes and their human implications

In keeping with PAGES concentration on paleoscience of relevance to human society, the volume closes with a set of papers which give an overview of the late Holocene. This period, beginning well after the end of the last glaciation and continuing right up to the present day, encompasses the development of present day human societies. The first paper, by Bradley, points out that even the last two centuries have experienced drastic extremes, including among the coldest and warmest decades in the

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