Geography Reference
In-Depth Information
non-intentional environmental effects. Deforestation, soil
degradation, and hillslope erosion have had a particularly long
history, and most early civilizations, from Mesopotamia to Middle
America, experienced major impacts of these processes. Physical
geographers recognized the seriousness of many of these impacts
over a century ago - as demonstrated, for example, by George
Perkins Marsh in
Man and Nature; or Physical Geography as
Modifi ed by Human Action
, published in 1864.
It is only since the Industrial Revolution, with the extensive
burning of fossil fuels, that there has been a signifi cant human
impact on global climate. Although the fi rst quantitative estimate
of the enhanced greenhouse effect produced by the release
of carbon dioxide was made by a Swedish scientist, Svante
Arrhenius, as early as 1896, it is only as we enter the 21st century
that the scale of the effects of such anthropogenic greenhouse-gas
pollution on the atmosphere is beginning clearly to exceed the
scale of the effects of natural climatic variability. In recognition of
the general prevalence of human impacts and the unprecedented
rates of change being induced throughout the geo-ecosphere, the
term 'Anthropocene' has been coined for the most recent 200
years or so of Earth's history (see box).
The environmental change theme in physical geography
has, therefore, been re-invigorated and has itself changed
as future climates due to enhanced global warming have
become not only a pervasive infl uence on the research agenda
in the natural environmental sciences but also a topic of
everyday conversation and an increasingly potent force on the
political agenda. Relatively long-term environmental change
is particularly important for the current focus on carbon
emissions as it provides a test bed for understanding the natural
carbon balance of the land-ocean-atmosphere system. The
shorter-term changes of the Holocene provide insights into the
contemporary natural background variability onto which the
