Today's date:
Spring 2005

Human Impact 0n Climate Has Made This the "Anthropocene Age"

PAUL J. CRUTZEN was awarded the Nobel Prize in Chemistry in 1995. He is currently a professor at the Max Planck Institute for Chemistry in Mainz, Germany, and at the Scripps Institution of Oceanography at the University of California, San Diego.

Mainz, Germany - For the past three centuries, the effects of humans on the global environment have escalated. Because of anthropogenic emissions of carbon dioxide, global climate may depart significantly from natural behavior for many millennia to come. It seems appropriate to assign the term "Anthropocene" to the present, in many ways a human-dominated, geological epoch, supplementing the Holocene-the warm period of the past 10 to 12 millennia.

The Anthropocene could be said to have started in the latter part of the 18th century, when analyses of air trapped in polar ice showed the beginning of growing global concentrations of carbon dioxide and methane. This period also happens to be when James Watt did his groundbreaking designs of steam engines.

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," referring to the "anthropozoic era."

In 1926, Russian geochemist Vladimir Vernadsky acknowledged the increasing impact of mankind: "the direction in which the processes of evolution must proceed, namely toward increasing consciousness and thought, and forms having greater and greater influence on their surroundings."

French paleontologist and philosopher Pierre Teilhard de Chardin and Vernadsky used the term "noosphere"-the "world of thought" - to mark the growing role of human brainpower in shaping humankind's 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. Nearly half 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 percent of the primary production in upwelling ocean regions and 35 percent in the temperate continental shelf.

Energy grew 16-fold during the 20th century, causing 160 million tons of atmospheric sulphur dioxide emissions per year, more than twice the sum of 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.

Over this same period, fossil-fuel burning and agriculture caused substantial increases in the concentrations of "greenhouse" gases-carbon dioxide by 30 percent and methane by more than 100 percent-reaching their highest levels in the past 400 millennia, with more increases to follow.

So far, these effects have largely been caused by only 25 percent 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 to 5.8 degrees Celsius 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).

Unless there is a global catastrophe-a meteorite impact, a world war or a pandemic-mankind will remain a major environmental force for many millennia. A daunting task lies ahead for scientists and engineers to guide society toward environmentally sustainable management during the era of the Anthropocene.

This will require appropriate human behavior at all scales, and may well involve internationally accepted, large-scale geo-engineering projects to accomplish such goals as "optimizing" climate. At this stage, however, we are still largely treading on terra incognita.