快猫短视频

MODERN agriculture is set to become as bad for the planet鈥檚 health as global
warming, a team of leading environmental scientists has warned. They list
rainforest destruction, nitrogen pollution and the spread of diseases such as
foot and mouth and BSE among the growing threats from agriculture.

鈥淭he environmental effects of agriculture are on a trajectory soon to rival
those of climate change,鈥� says David Tilman, an ecologist at the University of
Minnesota.

Tilman and nine other ecologists in the US forecast that over the next 50
years growing populations and an increasing demand for meat will mean the world
needs new farmland covering an area the size of the US. Meeting this demand will
probably see the destruction of 鈥渢he vast majority of the rainforests and
savannah grasslands in Latin America and central Africa, which harbour a large
portion of the Earth鈥檚 biological diversity鈥�, Tilman told 快猫短视频.

Animal diseases will be increasingly likely to spread to humans, the report
warns. 鈥淟ivestock are well-known to be a major source of human disease, and
current animal production methods may well be favouring the evolution of new
human pathogens,鈥� says Tilman.

The increased density of livestock also makes epidemics more likely. Foot and
mouth disease in Europe is the latest manifestation of this phenomenon, says
Tilman. 鈥淓pidemic losses of livestock are not a one-time fluke, but rather a
predictable outcome of high animal densities and low genetic diversity.鈥�

The study also predicts a pandemic of farm pollution, including fertilisers
and pesticides, that could upset ecosystems worldwide. Human activities already
release as much nitrogen and phosphorus into the environment as natural sources.
Much of this comes from farms, including unused fertiliser and livestock sewage.
It causes eutrophication鈥攖he over-fertilisation of soils and water that
results in the growth of toxic algae in lakes and coastal waters, poisoned
fisheries, nitrate-contaminated drinking water and acidified soils.

Eutrophication will double or triple worldwide in the next 50 years,
according to the study. A marine 鈥渄ead zone鈥� the size of New Jersey that has
formed in the Gulf of Mexico because of farm run-off down the Mississippi is a
sign of things to come, it says.

In developed countries, more than a third of all the nitrogen applied to
farms in fertiliser eventually emerges as animal waste that is discharged into
the environment. To counter this, Tilman calls for farmers to install equipment
to treat animal wastes from all intensive livestock units. 鈥淭hese cattle and hog
factories may contain 10,000 or more animals. They produce as much sewage as
human cities,鈥� he says. 鈥淏ut unlike human cities they are not required to treat
their sewage.鈥�

The 鈥渦nprecedented鈥� loss of biodiversity that Tilman predicts as a result of
farming will not only rival the impact of climate change, it could also
encourage it. In a separate paper in Nature, Tilman鈥檚 Minnesota colleague Peter
Reich shows that ecosystems that contain more species will be able to soak up
more carbon dioxide as atmospheric levels of the gas increase.

Degraded ecosystems with fewer species will be less good at this. 鈥淎
species-poor world,鈥� Reich concludes, 鈥渋s likely also to be a hotter world.鈥�