1
The Climate System: Its Functioning
and History
Sylvie Joussaume and Jean-Claude Duplessy
Climate plays an important role for mankind. It determines
the conditions in which societies can develop as well as the
resources available to them such as water and biological
inputs (agriculture, forests, livestock). However, climate is a
complex system. It is the result of interactions not only
between the atmosphere, the oceans, landmasses and ice but
also the biosphere: the living world. It varies depending on
the timescale, and different mechanisms may come into play
at different scales. The aim of this book is to show how a
multi-disciplinary scientific community can now reconstruct,
with increasing accuracy, the major features of past climates
and discover how they are regulated by the geological
evolution, geochemistry, physics and biology of our living
planet, Earth.
Human living conditions are dependent on climate, but
human beings, in turn, influence the climate system. They
change the atmospheric concentration of greenhouse gases
and aerosols, as well as the vegetation through deforestation
and agriculture. For this reason, it is of major importance to
society to understand how climate works and how man may
be altering its course. This is a complex scientific problem
because of the large number of feedbacks likely to occur and
the study of past climates contributes to a better understanding of them by analyzing major climate changes provoked by natural causes.
Climate Change
Definition of Climate
Climate is defined by the statistics of the physical characteristics of the atmosphere. It differs from meteorology by
focusing on statistics over several decades, by calculating
the average state of the atmosphere and its variability from
this average. In practice, climate is defined by the average
conditions over a thirty-year period. Although this working
definition makes sense while the weather is relatively stable,
it becomes more difficult to apply during a period of rapid
change. This was the case in the twentieth century during
which two phases of rapid increase in the average temperature of our planet were detected by weather stations in the
WMO network, one from 1910 to 1940 and the other from
1975 onwards (Fig. 1.1d). The period 1961–1990 is often
taken as a reference.
Climate Changes in the Past
Climate is essentially variable, regardless of the time scales
under consideration. Over past two millennia, historical
chronicles and earliest instrumental measurements dating
back to the seventeenth century have shown the existence of
a very cold period in Europe from the sixteenth to the
nineteenth century (the Little Ice Age), preceded by the
Medieval Warm Period and another warm period during
Roman times.
Geological data also show large upheavals in climate. Of
course, this is over much longer periods than thirty years, but
geologists strive to define a stratigraphic framework and
precise geochronology to put these events into context
within the history of our planet (Fig. 1.1). For example,
about seven hundred and fifty million years ago, the Earth
went through an intense glaciation phase; glaciers flowed
down to sea level on every continent, even in low latitudes,
to such an extent that our planet could be described as a
snowball. Conversely, during the Mesozoic Era (25–
65 million years), the conditions were hot, even at high
latitudes. During the Cenozoic Era (from 65 million years),
the glaciers grew slowly, first on the Antarctic continent and
then on Greenland. For the past three million years or so, the
Earth has experienced a succession of ice ages, marked by
glaciers advancing over land at high and middle latitudes of
S. Joussaume (&) Á J.-C. Duplessy
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191
Gif-sur-Yvette, France
e-mail: sylvie.joussaume@lsce.ipsl.fr
© Springer Nature Switzerland AG 2021
G. Ramstein et al. (eds.), Paleoclimatology, Frontiers in Earth Sciences,
https://doi.org/10.1007/978-3-030-24982-3_1
1
The Climate System: Its Functioning
and History
Sylvie Joussaume and Jean-Claude Duplessy
Climate plays an important role for mankind. It determines
the conditions in which societies can develop as well as the
resources available to them such as water and biological
inputs (agriculture, forests, livestock). However, climate is a
complex system. It is the result of interactions not only
between the atmosphere, the oceans, landmasses and ice but
also the biosphere: the living world. It varies depending on
the timescale, and different mechanisms may come into play
at different scales. The aim of this book is to show how a
multi-disciplinary scientific community can now reconstruct,
with increasing accuracy, the major features of past climates
and discover how they are regulated by the geological
evolution, geochemistry, physics and biology of our living
planet, Earth.
Human living conditions are dependent on climate, but
human beings, in turn, influence the climate system. They
change the atmospheric concentration of greenhouse gases
and aerosols, as well as the vegetation through deforestation
and agriculture. For this reason, it is of major importance to
society to understand how climate works and how man may
be altering its course. This is a complex scientific problem
because of the large number of feedbacks likely to occur and
the study of past climates contributes to a better understanding of them by analyzing major climate changes provoked by natural causes.
Climate Change
Definition of Climate
Climate is defined by the statistics of the physical characteristics of the atmosphere. It differs from meteorology by
focusing on statistics over several decades, by calculating
the average state of the atmosphere and its variability from
this average. In practice, climate is defined by the average
conditions over a thirty-year period. Although this working
definition makes sense while the weather is relatively stable,
it becomes more difficult to apply during a period of rapid
change. This was the case in the twentieth century during
which two phases of rapid increase in the average temperature of our planet were detected by weather stations in the
WMO network, one from 1910 to 1940 and the other from
1975 onwards (Fig. 1.1d). The period 1961–1990 is often
taken as a reference.
Climate Changes in the Past
Climate is essentially variable, regardless of the time scales
under consideration. Over past two millennia, historical
chronicles and earliest instrumental measurements dating
back to the seventeenth century have shown the existence of
a very cold period in Europe from the sixteenth to the
nineteenth century (the Little Ice Age), preceded by the
Medieval Warm Period and another warm period during
Roman times.
Geological data also show large upheavals in climate. Of
course, this is over much longer periods than thirty years, but
geologists strive to define a stratigraphic framework and
precise geochronology to put these events into context
within the history of our planet (Fig. 1.1). For example,
about seven hundred and fifty million years ago, the Earth
went through an intense glaciation phase; glaciers flowed
down to sea level on every continent, even in low latitudes,
to such an extent that our planet could be described as a
snowball. Conversely, during the Mesozoic Era (25–
65 million years), the conditions were hot, even at high
latitudes. During the Cenozoic Era (from 65 million years),
the glaciers grew slowly, first on the Antarctic continent and
then on Greenland. For the past three million years or so, the
Earth has experienced a succession of ice ages, marked by
glaciers advancing over land at high and middle latitudes of
S. Joussaume (&) Á J.-C. Duplessy
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191
Gif-sur-Yvette, France
e-mail: sylvie.joussaume@lsce.ipsl.fr
© Springer Nature Switzerland AG 2021
G. Ramstein et al. (eds.), Paleoclimatology, Frontiers in Earth Sciences,
https://doi.org/10.1007/978-3-030-24982-3_1
1