Past climate change - Climate Change: Biological and Human Aspects - page 110

and the Earth specifically, to exist. Asteroids and planetesimals are necessary in a
proto-planetary system for planets to form. In contrast, vulcanism is a manifestation
of the energy that drives plate tectonics, hence the deep carbon cycle, and so is a
major factor enabling allopatric speciation and biosphere stability (see the discussion
on ice-world recovery in section 3.2.2). Some of the main causes of mass extinctions
therefore relate to factors that enable life. Others, such as methane releases from
submarine methane hydrate (clathrates), wetlands and soils, ultimately arise out of
life itself. Life and mass extinction events are intricately connected well beyond the
obvious symmetry of one virtually being an antithesis of the other, and you cannot
have an extinction without life.
With regard to our current anthropogenic global warming and climate change, there
is much we can learn from the biosphere's history. There are perhaps two key points of
particular relevance. First, re-organisation of the carbon cycle, as we are now doing by
liberating formerly geologically isolated carbon into the atmosphere, results in major
environmental change. (A point that may seem obvious to many now, but which was
not so a decade or two ago; see the IPCC's first assessment, 1990.) Second, such
environmental change affects the number and range of species extant on the planet
both positively and negatively. This should be of considerable human concern, for not
only are we an animal species in our own right, but we rely on many species of plants
and animals for our daily survival. We rely on an even greater population of species
through what ecologists call ecosystem function, beyond the daily time frame, to
maintain environmental quality. We will return to these dimensions in later chapters.
3.5References
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