Geoscience Reference
In-Depth Information
already under considerable stress from other environmental and socio-economic
pressures.
The fact that human activities have caused most of the observed warming of
the climate system over the past half-century, primarily through the emission
of greenhouse gases, is now beyond reasonable doubt (IPCC, 2007). However,
climate change is only one of many changes to the global environment over the
past century or so that have been driven by the burgeoning human enterprise
(Steffen et al., 2004).
First, the current rate of extinction of biological species is 100 to 1,000 times
greater than the background rate (MA, 2005), suggesting that the earth may be
entering the sixth great extinction event in its history, but the first to be driven
by a biological species (
Homo sapiens
).
Moreover, human activities are now responsibility for 'fixing' more nitrogen
(converting unreactive to reactive forms) than all natural N-fixing processes
in the terrestrial biosphere combined (Galloway and Cowling, 2002). This
additional reactive nitrogen pollutes local lakes and rivers, reduces biodiversity
by fertilizing fast-growing species at the expense of rarer species that occupy
nutrient-poor niches and contributes the powerful greenhouse gas nitrous
oxide to the atmosphere. These and many other global-level changes to the
environment are shown in
Figure 7.1
(Steffen et al., 2004, and references
therein).
Accompanying these global environmental changes, and interacting with
them, is an equally far-reaching set of changes to the socio-economic fabric of
the human enterprise (
Figure 7.2
, Steffen et al., 2004, and references therein).
Changes include a rapid rise in human population, an even more dramatic rise in
economic activity, much greater exploitation - by rate, volume and extent - of
natural resources, and dramatic increases in transportation, trade and communi-
cation. Perhaps the most striking feature of
Figure 7.2
is the remarkable change
in rate of all 12 indicators around 1950, after the end of the Second World War.
This phenomenon has been called The Great Acceleration (Hibbard et al., 2006)
and marks a fundamental change in the human-environment relationship.
Taken together, the interacting socio-economic and environmental changes at
the planetary level depicted in
Figures 7.1
and
7.2
are often referred to as
global
change
. Perhaps an appropriate geological term - and concept - to define the
period of this profound shift is the
Anthropocene
.
The term Anthropocene was first proposed in 2000 by Nobel Laureate Paul
Crutzen (Crutzen and Stoermer, 2000; Crutzen, 2002). It is based on scientific
perceptions of the nature and impacts of recent global change and refers to the
fact that humans have now become so large in numbers and pervasive in activity
that they rival some of the great forces of Nature in their influence on the
functioning of the Earth System.
The influence of humans on the climate system is now well known, but human
activities are influencing the Earth System in many other ways. For example, the
acidity of the ocean is rising rapidly (Royal Society, 2005), over 50 per cent of
land ecosystems are now human dominated (Ellis et al., 2010), about a third of
