AN OVERVIEW OF CENTURY TIME-SCALE VARIABILITY
IN THE CLIMATE SYSTEM: OBSERVATIONS AND MODELS
THOMAS F. STOCKER
Climate and Environmental Physics
Bern, Switzerland
Contents
1 Introduction
2 Observations and Proxy Indicators
2.1 Direct Observations
2.2 Proxy Data . . . . . . .
3 Models and Mechanisms
3.1 Gyre-Thermohaline Circulation.
3.2 SST Anomalies in the Northwest Atlantic
3.3 Marginal Seas . . . . . . . . . . . . . . . .
3.4 Basin-Scale Thermohaline Circulation . .
3.5 The Southern Ocean-North Atlantic Connection
3.6 Other Mechanisms
4 Conclusions
Abstract
Estimates of the development of the Earth's climate subject to anthropogenic
forcing depend critically on our knowledge of natural climate variability on time
scales of decades to centuries. Time scales extracted from high-resolution proxy
records and observations indicate that the spectrum of climate variability exhibits
significant power in the range of decades to centuries superimposed on a red-noise
continuum. The classical view of climate variability is based on the concept that
observed fluctuations have their origin in periodic forcings on the same time scale,
i. e. that the climate system behaves like a linear system that is externally forced.
The present sensitivity of the climate system, however, would require strong positive
feedback mechanisms to translate the weak forcing signals (e.g. variability of solar
irradiation) into detectable fluctuations in observed and proxy variables. Instead, it
is proposed that these fluctuations are linked to interactions within and between the
different climate system components. An overview of recent modeling results and
the discussion of mechanisms involved show that such interactions internal to the
climate system cannot only exhibit the correct time scales but also easily account for
the amplitudes observed.
NATO AS! Series, Vol. 144
Decadal Climate Variability
Dynamics and Predictability
380
385
385
386
389
394
395
397
398
399
401
402
Edited by David L. T. Anderson and Jtirgen Willebrand
© Springer-Verlag Berlin Heidelberg 1996
IN THE CLIMATE SYSTEM: OBSERVATIONS AND MODELS
THOMAS F. STOCKER
Climate and Environmental Physics
Bern, Switzerland
Contents
1 Introduction
2 Observations and Proxy Indicators
2.1 Direct Observations
2.2 Proxy Data . . . . . . .
3 Models and Mechanisms
3.1 Gyre-Thermohaline Circulation.
3.2 SST Anomalies in the Northwest Atlantic
3.3 Marginal Seas . . . . . . . . . . . . . . . .
3.4 Basin-Scale Thermohaline Circulation . .
3.5 The Southern Ocean-North Atlantic Connection
3.6 Other Mechanisms
4 Conclusions
Abstract
Estimates of the development of the Earth's climate subject to anthropogenic
forcing depend critically on our knowledge of natural climate variability on time
scales of decades to centuries. Time scales extracted from high-resolution proxy
records and observations indicate that the spectrum of climate variability exhibits
significant power in the range of decades to centuries superimposed on a red-noise
continuum. The classical view of climate variability is based on the concept that
observed fluctuations have their origin in periodic forcings on the same time scale,
i. e. that the climate system behaves like a linear system that is externally forced.
The present sensitivity of the climate system, however, would require strong positive
feedback mechanisms to translate the weak forcing signals (e.g. variability of solar
irradiation) into detectable fluctuations in observed and proxy variables. Instead, it
is proposed that these fluctuations are linked to interactions within and between the
different climate system components. An overview of recent modeling results and
the discussion of mechanisms involved show that such interactions internal to the
climate system cannot only exhibit the correct time scales but also easily account for
the amplitudes observed.
NATO AS! Series, Vol. 144
Decadal Climate Variability
Dynamics and Predictability
380
385
385
386
389
394
395
397
398
399
401
402
Edited by David L. T. Anderson and Jtirgen Willebrand
© Springer-Verlag Berlin Heidelberg 1996