28
Climate and Astronomical Cycles
Didier Paillard
A Little History
From the Discovery of Ice Ages to the First
Climate Theories
The scientific notion that climate could evolve over time first
appeared along with the birth of paleoclimatology in the
nineteenth century when the existence of ice ages was discovered. Although the scientists of the time were aware that
the Earth had undergone many upheavals, notably through
the successions of various animal and vegetable fossil species, it was only when evidence of previous glacial periods
emerged that the idea of a changing climate really took
shape. The traces left behind by the movement of glaciers
during the last glacial period: moraines, erratic boulders,
glacial striations and features, were clearly identified in
many regions of Europe and North America and promoted
the idea that the climate, at least in the northern hemisphere,
may have been considerably colder in the past. The
nineteenth-century scientists’ point of view on glaciations
was quite different from ours, deeply rooted as it was in a
‘catastrophic’ perspective on the evolution of the Earth,
which was at that time imagined to have been punctuated by
‘deluges’ and other cataclysms, as highlighted in the excerpt
below.
The appearance of these large sheets of ice must have led to the
annihilation of all organic life on the surface of the earth. The
soil of Europe, formerly ornamented with tropical vegetation
and inhabited by troops of great elephants, enormous hippopotamuses and gigantic predators, was suddenly buried under
a vast mantle of ice covering the plains, lakes, seas and plateaus.
The movement of a powerful creation was succeeded by the
silence of death. The springs dried up, the rivers ceased to flow,
and the rays of the sun, rising on this frozen beach (that’s if they
reached it), were only greeted by the whistles of the northern
winds and the thunder of the crevasses that opened on the surface of this vast ocean of ice.
(L. Agassiz, Studies on glaciers, 1840)
For geologists of that era, climate changes were primarily
related to changes in topography. Although the continental
drift was not yet well established, the scientists tried to
explain their field observations by means of vertical movements of the continents: uplift of the mountains, erosion,
change in sea level etc. Under the influence of Charles Lyell,
these changes came to be seen as slow and progressive. The
assumption of catastrophism faded away to be replaced with
gradualism which presupposes that the modifications of the
Earth’s surface obey the physical laws that now apply but
over immensely long durations. This new point of view was
opposed to any external (especially heavenly) influence,
which no doubt explains the reluctance of geologists when
faced with the first astronomical theories of glaciations:
But though I am inclined to profit by Croll’s maximum eccentricity for the glacial period, I consider it quite subordinate to
geographical causes or the relative position of land and sea and
abnormal excess of land in polar regions.
(C. Lyell to C. Darwin, 1866)
The idea that the climate stems above all from geography
and topography has indeed merit. One need only look at the
etymology of the word climate (jkila = inclination, i.e. the
height of the Sun above the horizon, in other words, the
latitude of the location) or look for ‘climatology’ in an
academic organization chart to be convinced that this idea is
still valid. The physical principles underlying the functioning of the climate system were also updated in the nineteenth
century, notably by Joseph Fourier, who established the laws
of heat diffusion, explaining how heat is redistributed by the
surface fluids of the atmosphere and the ocean, and also
discussed the essential role of the greenhouse effect:
D. Paillard (&)
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91190
Gif-sur-Yvette, France
e-mail: Didier.Paillard@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_28
385
Climate and Astronomical Cycles
Didier Paillard
A Little History
From the Discovery of Ice Ages to the First
Climate Theories
The scientific notion that climate could evolve over time first
appeared along with the birth of paleoclimatology in the
nineteenth century when the existence of ice ages was discovered. Although the scientists of the time were aware that
the Earth had undergone many upheavals, notably through
the successions of various animal and vegetable fossil species, it was only when evidence of previous glacial periods
emerged that the idea of a changing climate really took
shape. The traces left behind by the movement of glaciers
during the last glacial period: moraines, erratic boulders,
glacial striations and features, were clearly identified in
many regions of Europe and North America and promoted
the idea that the climate, at least in the northern hemisphere,
may have been considerably colder in the past. The
nineteenth-century scientists’ point of view on glaciations
was quite different from ours, deeply rooted as it was in a
‘catastrophic’ perspective on the evolution of the Earth,
which was at that time imagined to have been punctuated by
‘deluges’ and other cataclysms, as highlighted in the excerpt
below.
The appearance of these large sheets of ice must have led to the
annihilation of all organic life on the surface of the earth. The
soil of Europe, formerly ornamented with tropical vegetation
and inhabited by troops of great elephants, enormous hippopotamuses and gigantic predators, was suddenly buried under
a vast mantle of ice covering the plains, lakes, seas and plateaus.
The movement of a powerful creation was succeeded by the
silence of death. The springs dried up, the rivers ceased to flow,
and the rays of the sun, rising on this frozen beach (that’s if they
reached it), were only greeted by the whistles of the northern
winds and the thunder of the crevasses that opened on the surface of this vast ocean of ice.
(L. Agassiz, Studies on glaciers, 1840)
For geologists of that era, climate changes were primarily
related to changes in topography. Although the continental
drift was not yet well established, the scientists tried to
explain their field observations by means of vertical movements of the continents: uplift of the mountains, erosion,
change in sea level etc. Under the influence of Charles Lyell,
these changes came to be seen as slow and progressive. The
assumption of catastrophism faded away to be replaced with
gradualism which presupposes that the modifications of the
Earth’s surface obey the physical laws that now apply but
over immensely long durations. This new point of view was
opposed to any external (especially heavenly) influence,
which no doubt explains the reluctance of geologists when
faced with the first astronomical theories of glaciations:
But though I am inclined to profit by Croll’s maximum eccentricity for the glacial period, I consider it quite subordinate to
geographical causes or the relative position of land and sea and
abnormal excess of land in polar regions.
(C. Lyell to C. Darwin, 1866)
The idea that the climate stems above all from geography
and topography has indeed merit. One need only look at the
etymology of the word climate (jkila = inclination, i.e. the
height of the Sun above the horizon, in other words, the
latitude of the location) or look for ‘climatology’ in an
academic organization chart to be convinced that this idea is
still valid. The physical principles underlying the functioning of the climate system were also updated in the nineteenth
century, notably by Joseph Fourier, who established the laws
of heat diffusion, explaining how heat is redistributed by the
surface fluids of the atmosphere and the ocean, and also
discussed the essential role of the greenhouse effect:
D. Paillard (&)
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91190
Gif-sur-Yvette, France
e-mail: Didier.Paillard@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_28
385