–21) is devoted to the slow and complex work of reconstruction by applying this whole range
of indicators. Thus, we can reconstruct the climate of the major components of the climate
system: the atmosphere, the ocean, the cryosphere, and the biosphere. But we can also take
advantage of the specificities of temperate or tropical lakes, of caves and their concretions
(speleothems), of tree rings and even, more recently, of harvesting dates (Chap. 17). How can
paleo-winds or, to put it in more scientific jargon, the variations in atmospheric dynamics be
reconstructed? Based on the isotopic composition of precipitation (Chap. 10) or of the loess
(Chap. 13), not only can the evolution of the surface and deep ocean be reconstructed, but also
the geometry and dynamics of large water masses (Chap. 21). For land surfaces, palynology
and dendroclimatology enable us to retrace the evolution of vegetation and climate, respectively (Chaps. 12 and 16). Finally, the cores taken from the ice caps of both hemispheres make
it possible to reconstruct the polar climate (Chap. 11).
In addition to these two main concepts, we also need to understand how fluctuations in the
hydrology of the tropics have caused variations in lakes (Chaps. 18 and 19) and glaciers
(Chap. 20); these factors also tell a part of the climate story. Other markers, such as speleothems (Chap. 14) or lake ostracods (Chap. 15) reveal changes in climate in more temperate
areas.
Thus, a description of the global climate emerges from the local or regional climate
reconstructions. Through coupling these reconstructions with dating, our knowledge of climate evolution progresses constantly. Nevertheless, this image is both fragmentary, because
of the strong geographic and temporal disparity of our knowledge, and unclear, because of the
uncertainties in the reconstructions that the paleoclimatologist tries to reduce. There is still a
long way to go in terms of developing new indicators and improving those widely used in
order to complete and refine this description.
The second volume of this book (Chaps. 22–30) focuses on the major processes and
mechanisms explaining the evolution of past climate from geological to historical timescales,
whereas last Chap. 31 examines future climate projections. First of all, we address, in the very
long term, the interactions between tectonics and climate over the timescale of tens to hundreds of millions of years (Chap. 22). Then, we deal with the biogeochemical cycles that
govern the concentrations of greenhouse gases in the atmosphere over the last million years
(Chap. 23). And finally, we consider the interactions with ice caps (Chap. 24).
We will continue our journey simulating the climate evolution through time from the
formation of the Earth (4.6 billion years ago) up to the future climates at scales from a few tens
of thousands to a hundred of years. On this journey, it becomes obvious that the dominant
processes, those that drive climate change, vary according to timescales: solar power, which
increases by about 7% every billion years places its stamp on very long-term evolution,
whereas at the scale of tens of millions of years, it is tectonics that sculpt the face of the Earth,
from the high mountain ranges to the bathymetry of the ocean floor. Finally, ‘the underlying
rhythm of Milankovitch,’ with a much faster tempo of a few tens of thousands of years can
produce, if the circumstances permit, the glacial–interglacial cycles described in the preceding
parts. On top of this interconnection of timescales, a broad range of processes and components
of the climate system is superimposed. Through these chapters, we would like to highlight the
need to model a complex system where different constituents interact at different timescales
(Chap. 25). With the development of these models, the scope of investigation is vast. Indeed,
ranging from recent Holocene climates (Chap. 30) to geological climates (Chaps. 26 and 27),
how they evolve is underpinned by very different processes: from plate tectonics (Chap. 22) to
orbital parameters (Chap. 28). The complexity of the system can also be seen in the abrupt
reorganizations of the ocean–atmosphere system (Chap. 29). The capacity acquired in recent
decades to replicate past climate changes using a hierarchy of models, and to compare these
results with different types of data, has demonstrated the relevance of this approach coupling
model simulations with data acquisition.
xvi
Preface
of indicators. Thus, we can reconstruct the climate of the major components of the climate
system: the atmosphere, the ocean, the cryosphere, and the biosphere. But we can also take
advantage of the specificities of temperate or tropical lakes, of caves and their concretions
(speleothems), of tree rings and even, more recently, of harvesting dates (Chap. 17). How can
paleo-winds or, to put it in more scientific jargon, the variations in atmospheric dynamics be
reconstructed? Based on the isotopic composition of precipitation (Chap. 10) or of the loess
(Chap. 13), not only can the evolution of the surface and deep ocean be reconstructed, but also
the geometry and dynamics of large water masses (Chap. 21). For land surfaces, palynology
and dendroclimatology enable us to retrace the evolution of vegetation and climate, respectively (Chaps. 12 and 16). Finally, the cores taken from the ice caps of both hemispheres make
it possible to reconstruct the polar climate (Chap. 11).
In addition to these two main concepts, we also need to understand how fluctuations in the
hydrology of the tropics have caused variations in lakes (Chaps. 18 and 19) and glaciers
(Chap. 20); these factors also tell a part of the climate story. Other markers, such as speleothems (Chap. 14) or lake ostracods (Chap. 15) reveal changes in climate in more temperate
areas.
Thus, a description of the global climate emerges from the local or regional climate
reconstructions. Through coupling these reconstructions with dating, our knowledge of climate evolution progresses constantly. Nevertheless, this image is both fragmentary, because
of the strong geographic and temporal disparity of our knowledge, and unclear, because of the
uncertainties in the reconstructions that the paleoclimatologist tries to reduce. There is still a
long way to go in terms of developing new indicators and improving those widely used in
order to complete and refine this description.
The second volume of this book (Chaps. 22–30) focuses on the major processes and
mechanisms explaining the evolution of past climate from geological to historical timescales,
whereas last Chap. 31 examines future climate projections. First of all, we address, in the very
long term, the interactions between tectonics and climate over the timescale of tens to hundreds of millions of years (Chap. 22). Then, we deal with the biogeochemical cycles that
govern the concentrations of greenhouse gases in the atmosphere over the last million years
(Chap. 23). And finally, we consider the interactions with ice caps (Chap. 24).
We will continue our journey simulating the climate evolution through time from the
formation of the Earth (4.6 billion years ago) up to the future climates at scales from a few tens
of thousands to a hundred of years. On this journey, it becomes obvious that the dominant
processes, those that drive climate change, vary according to timescales: solar power, which
increases by about 7% every billion years places its stamp on very long-term evolution,
whereas at the scale of tens of millions of years, it is tectonics that sculpt the face of the Earth,
from the high mountain ranges to the bathymetry of the ocean floor. Finally, ‘the underlying
rhythm of Milankovitch,’ with a much faster tempo of a few tens of thousands of years can
produce, if the circumstances permit, the glacial–interglacial cycles described in the preceding
parts. On top of this interconnection of timescales, a broad range of processes and components
of the climate system is superimposed. Through these chapters, we would like to highlight the
need to model a complex system where different constituents interact at different timescales
(Chap. 25). With the development of these models, the scope of investigation is vast. Indeed,
ranging from recent Holocene climates (Chap. 30) to geological climates (Chaps. 26 and 27),
how they evolve is underpinned by very different processes: from plate tectonics (Chap. 22) to
orbital parameters (Chap. 28). The complexity of the system can also be seen in the abrupt
reorganizations of the ocean–atmosphere system (Chap. 29). The capacity acquired in recent
decades to replicate past climate changes using a hierarchy of models, and to compare these
results with different types of data, has demonstrated the relevance of this approach coupling
model simulations with data acquisition.
xvi
Preface