INDEX: Endangered planet

* Human activity is putting such severe strain on Earth's natural functions that the ability of the planet's ecosystems to sustain future generations can no longer be taken for granted. The provision of food, fresh water, energy and materials to a growing population has come at considerable cost to the complex system of plants, animals, and biological processes that make the planet habitable.

* The 2005 Millennium Ecosystems Assessment predicts that between 10% and 15% of still-existing plant species will be extinct by 2050. It found that 23% of mammal species, 12% of bird species, and 32% of amphibian species are also threatened with extinction.

* Over the past few hundred years, humans have increased the species extinction rate by as much as 1,000 times the rates that prevailed over the planet's previous history. In some sea areas, the total weight of fish available to be caught and consumed is less than a hundredth of that caught before the onset of industrial fishing.

* The dominance of coal, oil and natural gas as our sources of energy has released large quantities of carbon previously locked underground, and has increased the atmospheric concentration of carbon dioxide by 34% since 1750. The global warming thus caused is accelerating the speed of climate change at a pace greater than anything seen for at least 10,000 years.

* Among the anticipated consequences of increased global temperatures are 1) flooding as polar ice-caps melt, raising sea levels; 2) extreme weather events due to shifting ocean currents; and 3) the expansion of deserts as land dries up.

* Water withdrawals from rivers and lakes for irrigation, household and industrial use have doubled in the last 40 years, reducing the flow of several major rivers, including the Nile, Yellow and Colorado Rivers. The construction of dams along rivers has also greatly restricted their flows. In some regions, such as the Middle East and North Africa, humans use 120% of renewable water supplies due to their reliance on groundwater that is not recharged.

* Climate change threatens farming, which is dependent on climatic stability. Scientists in Asia fear that rising temperatures will reduce grain yields in the tropics by as much as 30% by mid-century. Nearly a quarter of Earth's terrestrial surface has been converted to cropland to feed the growing human population, so the expected drastic change in climate threatens to make an already unacceptable rate of global hunger even worse.

* More than half of all the synthetic nitrogen fertilizer ever used has been used since 1985. Human activities have now roughly doubled the rate of creation of reactive nitrogen on the land surface and tripled the flow of phosphorus into the oceans.

SOURCES: Millennium Ecosystem Assessment 2005; UN Environment Program; David Suzuki and Amanda McConnell, The Sacred Balance, 2002.