Global Warming and Paul J. Crutzen Essay

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Geology of mankind
Paul J. Crutzen

or the past three centuries, the effects of humans on the global environment have escalated. Because of these anthropogenic emissions of carbon dioxide, global climate may depart significantly from natural behaviour for many millennia to come. It seems appropriate to assign the term ‘Anthropocene’ to the present, in many ways human-dominated, geological epoch, supplementing the Holocene — the warm period of the past 10–12 millennia. The
Anthropocene could be said to have started in the latter part of the eighteenth century, when analyses of air trapped in polar ice showed the beginning of growing global concentrations of carbon dioxide and methane. This date also happens to coincide with James Watt’s design of the steam engine in 1784.
Mankind’s growing influence on the environment was recognized as long ago as
1873, when the Italian geologist Antonio
Stoppani spoke about a “new telluric force which in power and universality may be compared to the greater forces of earth,”

F

NATURE | VOL 415 | 3 JANUARY 2002 | www.nature.com

referring to the “anthropozoic era”. And in 1926, V. I. Vernadsky acknowledged the increasing impact of mankind: “The direction in which the processes of evolution must proceed, namely towards increasing consciousness and thought, and forms having greater and greater influence on their surroundings.” Teilhard de Chardin and
Vernadsky used the term ‘noösphere’ — the
‘world of thought’ — to mark the growing role of human brain-power in shaping its own future and environment.
The rapid expansion of mankind in numbers and per capita exploitation of
Earth’s resources has continued apace.
During the past three centuries, the human population has increased tenfold to more than 6 billion and is expected to reach 10 billion in this century. The methane-producing cattle population has risen to 1.4 billion.
About 30–50% of the planet’s land surface is exploited by humans. Tropical rainforests disappear at a fast pace, releasing carbon dioxide and strongly increasing species extinction. Dam building and river diversion have become commonplace. More than half of all accessible fresh water is used by mankind. Fisheries remove more than 25% of the primary production in upwelling ocean regions and 35% in the temperate continental shelf. Energy use has grown
16-fold during the twentieth century, causing 160 million tonnes of atmospheric sulphur dioxide emissions per year, more than twice the sum of its natural emissions.
More nitrogen fertilizer is applied in agriculture than is fixed naturally in all terrestrial ecosystems; nitric oxide production by the burning of fossil fuel and biomass also overrides natural emissions.
Fossil-fuel burning and agriculture have caused substantial increases in the concentrations of ‘greenhouse’ gases — carbon dioxide by 30% and methane by more than
100% — reaching their highest levels over the past 400 millennia, with more to follow.
So far, these effects have largely been caused by only 25% of the world population. The consequences are, among others, acid precipitation, photochemical ‘smog’ and climate warming. Hence, according to the latest estimates by the Intergovernmental Panel on Climate Change (IPCC), the
Earth will warm by 1.4–5.8 °C during this century. Many toxic substances are released into the environment, even some that are not toxic at all but nevertheless have severely damaging effects, for example the chlorofluorocarbons that caused the Antarctic
‘ozone hole’ (and which are now regulated).
Things could have become much worse: the
© 2002 Macmillan Magazines Ltd

The Anthropocene
The Anthropocene could be said to have started in the late eighteenth century, when analyses of air trapped in polar ice showed the beginning of growing global concentrations of carbon dioxide and methane. ozone-destroying properties of
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