About 6% of the earth's land surface has been radically transformed to structures such as settlements, roads, and reservoirs.

The net loss of forests through human activity is about 8 million km2, approximately the size of the continental US; 3/4 of that amount has been cleared in the last 300 years. Much of this has been added to the 15 million km2 now used for cropland.

The annual human withdrawal of water from natural circulation is about 3,600 km3, an amount exceeding Lake Huron's volume.

Sediment load of large rivers in regions of major human activity has increased threefold; that of small rivers has multiplied eightfold.

The atmosphere's concentration of methane has doubled since the mid-eighteenth century.

An area the size of France is submerged beneath the earth's artificial reservoirs.

Global irrigated agriculture has jumped from 80,000 km2 in 1800, to 2,200,000 km2 in 1984; about half of all irrigated land is affected to some degree by secondary salination.

The human population first reached 1 billion about 175 years ago. Since then each new billion has been added at shorter intervals: in 115 years, 35 years, 15 years, and 11-12 years.

The number of cities exceeding a million in population jumped from 16 in 1900, to about 400 today.

In the last 300 years, the human population has shifted from being almost totally rural, to over 40% living in urban areas.

In many categories -- population growth, water withdrawals, and cumulative releases of sulfur, phosphorus, nitrogen, lead, and many organic chemicals -- half of the totality of humankind's transformation of the earth has occurred since World War II.

15% of all plant species are believed to be threatened with extinction.

* BL Turner, editor; 1990; Cambridge University Press with Clark University; Cambridge, England; 713 pp.