T. M. Lentona and W. von Blohb
Geophys. Res. Lett. 28, no. 9, 1715-1718 (2001)
a Centre for Ecology and Hydrology, Bush Estate, Penicuik,
Midlothian EH26 0QB, UK.
bPotsdam Institute for Climate Impact Research (PIK),
Telegrafenberg, P.O. Box 60 12 03, 14412 Potsdam, Germany.
The Sun is becoming more luminous with time and will eventually
overheat the biosphere. However, life cools the Earth by
amplifying the rate of silicate rock weathering and maintaining a
low level of atmospheric CO2. Recent studies indicate a much
stronger biotic weathering effect than in models used to estimate
the life span of the biosphere. Here we show that the resulting
feedback lengthens the survival of complex life by delaying the
loss of CO2 from the atmosphere. The weathering biota can
potentially maintain the Earth in a habitable state when otherwise
it would be too hot for them. If so, catastrophic warming rather
than gradual CO2 starvation will terminate complex life.
Despite the possibility of an irreversible collapse, the current
biosphere should remain resilient to carbon cycle perturbation or
mass extinction events for at least 0.8 Gyr and may survive for
up to 1.2 Gyr.
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Figure: Earth system state as a function of biotic amplification
factor (alpha) and time or corresponding solar luminosity
(Seff). Total biotic amplification of weathering is
beta = 1.56 alpha. In the `Biotic' region, only the solution
with life is stable. In the `Abiotic' region, only the solution
without life is stable. `Biotic + Abiotic' indicates the bi-stable
regime in which solutions with and without life are both stable.
(a) Geostatic case. (b) Geodynamic case.