Geoscience Reference
In-Depth Information
chemical element, phosphorus, which had become concentrated in a
few deposits by biogeochemical flows over millions of years. Some
researchers have calculated that, considering the current rate of
phosphorus use, the few exploitable P reserves may be exhausted in
less than a hundred years (Table 4.3). As there is no substitute for
phosphorus, human societies could not, in all likelihood, replace this
element with any other, unlike hydrocarbons that humans hope to
replace with different forms of carbon-free, renewable energy when
the reserves are exhausted. Exploitable land deposits of P will be
exhausted by human societies over the next decades, but their natural
replenishment will take hundreds of millions of years. Will the next
crisis faced by human societies be about phosphorus? Will countries
fight over this essential and rare chemical element?
4.7. Biogeochemical equilibria and human societies: problems
The effects of the current anthropogenic disturbances of
biogeochemical equilibria will differ according to the time scale
considered. The following paragraphs briefly examine some
relationships that exist between biogeochemical equilibria and human
societies on three different time scales, i.e. millions of years (very
long term), centuries to millennia (long term), and decades to
centuries (human societies). Section 2.5 in Chapter 2 of [MON 14b]
provides a wider perspective that includes ecosystems.
Over millions of years, some very long-term biogeochemical
cycles have the potential to maintain the stationary state of different
chemical elements in Earth's reservoirs. For example, the carbonate-
silicate cycle (section 4.3.2, equations [4.6]-[4.9]) can regulate the
concentration of atmospheric CO
2
and, therefore, the climate of Earth
over millions of years. This type of very long-term regulation will
likely cancel out most of the current anthropogenic disturbances,
whose duration will have been very short compared with the very
long-term biogeochemical cycles.
On a scale of a few centuries to millennia, the long-term
biogeochemical cycles can mitigate some disturbances to the natural
biogeochemical cycles by human societies. One example is the
