For the past three centuries, humans' effects on the global environment have escalated.

Most important, our emissions of carbon dioxide may cause global climate patterns to depart significantly from their natural course for many millennia to come.

It seems appropriate to assign the term "Anthropocene" to the current, in many ways human-dominated, geological epoch, supplementing the Holocene - the warm period of the past 10 to 12 millennia.

The Anthropocene Period 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 date 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 referred to the "anthropozoic era," defined by a "new telluric force, which in power and universality may be compared to the greater forces of earth."

Humans' rapid expansion in terms of population and per capita use of Earth's resources has continued apace. During the past three centuries, the human population has increased 10-fold, to more than six billion.

As a result, 30-50 percent of the planet's land surface is now exploited by humans. At the same time, the methane-producing cattle population has risen to 1.4 billion, contributing to the increasing rate of destruction of tropical rainforests, which releases carbon dioxide and contributes to faster species extinction.

Soil erosion

Land conversion for grazing (and construction), together with crop tillage, has also caused soil erosion at 15 times its natural rate. Indeed, at its current pace, anthropogenic soil erosion would fill the Grand Canyon in 50 years.

Similarly, dam building and river diversion have become commonplace, as humans' water consumption has risen nine-fold over the past century, to the point that mankind now uses more than half of all accessible fresh water - roughly two-thirds of it for agriculture.

Moreover, energy use has grown 16-fold during the 20th century, causing 160 million tons of atmospheric sulfur-dioxide emissions per year - more than twice the total of natural emissions.

Likewise, more nitrogen fertilizer is applied in agriculture than is fixed naturally in all terrestrial ecosystems, and nitric-oxide production from the burning of fossil fuels and biomass also surpasses natural emissions.

At the same time, human consumption of fossil fuels, together with our agricultural activities, have caused substantial increases in concentrations of "greenhouse" gases - CO2 by 30 percent and methane by more than 100 percent.

Indeed, these concentrations are higher than at any point in the past 400 millennia, with more growth to follow, because so far these effects have largely been caused by only 25 percent of the world population.

Global warming

The consequences are numerous and profound: acid precipitation, photochemical "smog" and global warming, among others.

Many toxic substances are released into the environment, even some that are not toxic but nonetheless are highly damaging - for example, the chlorofluorocarbons that caused the Antarctic ozone hole (and which are now regulated).

Things could have become much worse: the ozone-destroying properties of halogens have been studied since the mid-1970s.

If it had turned out that chlorine behaved chemically like bromine, the ozone hole would by then have been a global, year-round phenomenon, not just an event of the Antarctic spring.

More by luck than by wisdom, this catastrophic situation did not develop.

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.

As a result, scientists and engineers face a daunting task during the Anthropocene era: to guide us towards environmentally sustainable management. At this stage, however, we are still largely treading on terra incognita.

(Shanghai Daily June 9, 2009)