The End of Earthly Oceans - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 205

the combination of carbon dioxide in the atmosphere with rocks at
the surface, to produce dissolved carbonate and bicarbonate ions that
wash into the sea, ultimately to produce limestones. This could lead
to atmospheric carbon dioxide falling to low levels. For some hun-
dreds of millions of years, this effect might be sufficiently strong to
overcome the increasing heat of the sun.
Entangled in this, though, is the effect on life: an important regula-
tor of carbon dioxide levels on Earth, both through its processing
and storing of carbon, and also—via the catalytic effects of surface
microbial colonies and the presence of soils, plant roots, and such—
increasing the rate of chemical weathering (and therefore of carbon
drawdown) at the surface. If carbon dioxide levels fall sufficiently low
then plants may not be able to photosynthesize and would die out,
likely acting as a brake on the further drawdown of atmospheric
carbon dioxide by surface weathering.
There will be other factors at work, not least the changing pattern
of oceans and continents, to alter the way in which ocean currents
flow. It is a complex multi-dimensional puzzle, and the fight between
icehouse and greenhouse conditions on our planet may continue for
some time. But then, there will inevitably come the end of oceans.
The Moist Greenhouse
At some stage in the future, no matter what happens to atmospheric
carbon dioxide levels, the Sun's heat will take the upper hand. This is
the beginning of the end of the Earth's oceans. As the Earth warms,
towards mean temperatures that will rise into the forties and then
into the fifties Celsius, more and more seawater will evaporate and the
atmosphere—warmer too—will become increasingly charged with
water vapour. We humans, who love temperate conditions, would
find conditions unbearably humid were we able to visit this inescap-
able future state of our planet. If we could cope with such conditions