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| Titel |
Atmospheric carbon dioxide and the long-term control of the Earth's climate |
| VerfasserIn |
J. H. Carver, I. M. Vardavas |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 13, no. 7 ; Nr. 13, no. 7, S.782-790 |
| Datensatznummer |
250011921
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| Publikation (Nr.) |
 copernicus.org/angeo-13-782-1995.pdf |
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| Zusammenfassung |
| A CO2-weathering model has been
used to explore the possible evolution of the Earth's climate as the Sun
steadily brightened throughout geologic time. The results of the model
calculations can be described in terms of three, qualitatively different, "Megaclimates".
Mega-climate 1 resulted from a period of rapid outgassing in the early Archean,
with high, but declining, temperatures caused by the small weathering rates on a
largely water-covered planet. Mega-climate 2 began about 3 Gyear ago as major
continental land masses developed, increasing the weathering rate in the early
Proterozoic and thereby depleting the atmospheric CO2 concentration.
This process produced the first Precambrian glaciations about 2.3 Gyear ago.
During Mega-climate 2, evolutionary biological processes increased the surface
weatherability in incremental steps and plate tectonics modulated the CO2
outgassing rate with an estimated period of 150 Myear (approximately one-half
the period for the formation and breakup of super continents). Throughout
Mega-climate 2 the surface temperature was controlled by variations in the
atmospheric CO2 level allowing transitions between glacial and
non-glacial conditions. The results of the model for Mega-climate 2 are in
agreement with the occurrence (and absence) of glaciations in the geologic
record. Extending the model to the future suggests that CO2 control
of the Earth's temperature will no longer be able to compensate for a solar flux
that continues to increase. The present level of atmospheric CO2 is
so small that further reduction in CO2 cannot prevent the Earth from
experiencing Mega-climate 3 with steadily increasing surface temperatures caused
by the continued brightening of the Sun. During Mega-climate 3, the main danger
to the biosphere would come not from an increasing temperature but from a
decreasing (rather than an increasing) CO2 level which could, in
time, fall below 0.5 PAL, causing serious damage to the biosphere. Fortunately,
the rates of change due to solar brightening are slow enough that Mega-climate 3
appears to pose no threat to the biosphere for the next 0.5-2 Gyear. |
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