physical, chemical, and biological phenomena that govern the functioning of the climate
system and shows how it is possible to reconstruct the variations in the past at all timescales.
This is the work of paleoclimatologists. As soon as the means became available to them in
the second half of the twentieth century, they undertook to track down all traces of climate
change so as to establish a planetary vision. This led them to develop new methods of
sampling continental sediments, marine sediments in the context of major oceanographic
campaigns, and ice cores by carrying out large-scale drilling campaigns of mountain glaciers
and the ice sheets of Greenland and of Antarctica. The level of resources that needs to be
mobilized is such that the drilling campaigns of polar ice and of marine sediments from all the
world’s oceans could only be carried out in an international cooperative framework which
makes it possible to coordinate the efforts of the various teams.
This scientific investment has produced an abundant harvest of samples containing records
of past climates. On the continents, lake sediments; peat bogs; concretions in caves; and fossil
tree rings have provided many indicators of environmental conditions, especially of the
behavior of vegetation and the atmosphere. In the ocean, samples have been taken from all
of the large basins and cores are able to trace the history of the last tens of millions of years.
Finally, the large drillings in the ice sheets have provided information not only on polar
temperatures, but also on the composition of the atmosphere (dust and the concentrations of
greenhouse gases, such as carbon dioxide and methane).
Unfortunately, nature has no paleothermometer or paleopluviometer, and therefore, there is
no direct indicator of the changes in temperature or precipitation: Everything has had to be
built from scratch, not only to reconstruct the climates, but also to date them. Extracting a
reconstruction of the evolution of the climate from these samples has necessitated considerable
developments using the most innovative methods from the fields of geochemistry, biology,
and physics. Firstly, it was essential to establish a timeframe to know which period was
covered by each sample. Many methods were developed, and they are the subject of the
second part of this book. Radioactive decay, which is governed by strict physical laws, plays a
vital role. It has made it possible to obtain timescales converted into calendar years, and it has
provided clarification on stratigraphic geology. Other more stratigraphic approaches have been
implemented: identification of characteristic events that need to be dated elsewhere; counting
of annual layers; or modeling of ice flow. It has thus been possible to establish a chronological
framework, and paleoclimatologists are now trying to make it common to all data via an
on-going effort to make multiple correlations between the various recordings. Few climatologists rely on one indicator. The confidence that they have in reconstructing a climate change
at a given time is obtained by intersecting reconstructions from independent indicators but also
by confronting them with results from models. Methods of reconstructing the evolution of the
different components of the climate system from geological indicators then had to be developed. These are extremely varied, and their description constitutes the main and third part of
volume I. Many use the latest developments in paleomagnetism, geochemistry, and statistical
methods to empirically link the distribution of fossil plants and animals with environmental
parameters, primarily air and water temperature. Reconstructions achieved in this way have
now reached a level of reliability such that, for certain periods, not only qualitative variations
(in terms of hot/cold, dry/wet) can be obtained, but even quantitative ones with the associated
uncertainties also quantified. This is the level of climate reconstruction necessary to allow
comparison with climate models.
The use of climate models also gained momentum during the second half of the twentieth
century. First established to simulate atmospheric circulation, they have progressed by integrating more and more efficiently the physics, processes, and parameterization of the radiative
budget and the hydrological cycle, in particular, by incorporating satellite data. However, the
atmosphere only represents the rapid component of the climate system.
The late 1990s dramatically demonstrated the need to link atmospheric models to global
patterns of the ocean and vegetation to reconstruct climate change. Indeed, teams from the
GISS in the USA and from Météo-France bolstered by their atmospheric models that had
x
Introduction
system and shows how it is possible to reconstruct the variations in the past at all timescales.
This is the work of paleoclimatologists. As soon as the means became available to them in
the second half of the twentieth century, they undertook to track down all traces of climate
change so as to establish a planetary vision. This led them to develop new methods of
sampling continental sediments, marine sediments in the context of major oceanographic
campaigns, and ice cores by carrying out large-scale drilling campaigns of mountain glaciers
and the ice sheets of Greenland and of Antarctica. The level of resources that needs to be
mobilized is such that the drilling campaigns of polar ice and of marine sediments from all the
world’s oceans could only be carried out in an international cooperative framework which
makes it possible to coordinate the efforts of the various teams.
This scientific investment has produced an abundant harvest of samples containing records
of past climates. On the continents, lake sediments; peat bogs; concretions in caves; and fossil
tree rings have provided many indicators of environmental conditions, especially of the
behavior of vegetation and the atmosphere. In the ocean, samples have been taken from all
of the large basins and cores are able to trace the history of the last tens of millions of years.
Finally, the large drillings in the ice sheets have provided information not only on polar
temperatures, but also on the composition of the atmosphere (dust and the concentrations of
greenhouse gases, such as carbon dioxide and methane).
Unfortunately, nature has no paleothermometer or paleopluviometer, and therefore, there is
no direct indicator of the changes in temperature or precipitation: Everything has had to be
built from scratch, not only to reconstruct the climates, but also to date them. Extracting a
reconstruction of the evolution of the climate from these samples has necessitated considerable
developments using the most innovative methods from the fields of geochemistry, biology,
and physics. Firstly, it was essential to establish a timeframe to know which period was
covered by each sample. Many methods were developed, and they are the subject of the
second part of this book. Radioactive decay, which is governed by strict physical laws, plays a
vital role. It has made it possible to obtain timescales converted into calendar years, and it has
provided clarification on stratigraphic geology. Other more stratigraphic approaches have been
implemented: identification of characteristic events that need to be dated elsewhere; counting
of annual layers; or modeling of ice flow. It has thus been possible to establish a chronological
framework, and paleoclimatologists are now trying to make it common to all data via an
on-going effort to make multiple correlations between the various recordings. Few climatologists rely on one indicator. The confidence that they have in reconstructing a climate change
at a given time is obtained by intersecting reconstructions from independent indicators but also
by confronting them with results from models. Methods of reconstructing the evolution of the
different components of the climate system from geological indicators then had to be developed. These are extremely varied, and their description constitutes the main and third part of
volume I. Many use the latest developments in paleomagnetism, geochemistry, and statistical
methods to empirically link the distribution of fossil plants and animals with environmental
parameters, primarily air and water temperature. Reconstructions achieved in this way have
now reached a level of reliability such that, for certain periods, not only qualitative variations
(in terms of hot/cold, dry/wet) can be obtained, but even quantitative ones with the associated
uncertainties also quantified. This is the level of climate reconstruction necessary to allow
comparison with climate models.
The use of climate models also gained momentum during the second half of the twentieth
century. First established to simulate atmospheric circulation, they have progressed by integrating more and more efficiently the physics, processes, and parameterization of the radiative
budget and the hydrological cycle, in particular, by incorporating satellite data. However, the
atmosphere only represents the rapid component of the climate system.
The late 1990s dramatically demonstrated the need to link atmospheric models to global
patterns of the ocean and vegetation to reconstruct climate change. Indeed, teams from the
GISS in the USA and from Météo-France bolstered by their atmospheric models that had
x
Introduction