A new worldwide environmental survey says humans are damaging the planet at an unprecedented rate and causing irreversible changes to the world's ecosystems. 

The study says a rising human population has polluted or over-exploited almost two thirds of Earth's ecosystem during the past 50 years.  More than 1,300 scientists and researchers from around the world contributed to the four-year study for the United Nations. 

The Millennium Ecosystems Assessment Report concludes that 15 of 24 ecosystems -- including oceans, forests and grasslands -- are being damaged by human population growth and global warming.

Dr. Hal Mooney

The co-chair of the United Nations study, Dr. Hal Mooney, says, "We've altered the fundamental ecosystem base more rapidly, and extensively than any time, any comparable period of time in history."

The report says the 50 years of changes in ecosystems are partially due to a growing demand for food, fresh water, timber and fuel.  

Since 1945, more land has been converted to agriculture, than in the in the 18th and 19th centuries combined.  At least a quarter of all fish stocks are over-harvested.  Ten to 30 percent of mammal, bird and amphibian species are currently threatened with extinction.  One-third of the world's population is living in water scarce or water stressed areas, and this is projected to double over the next 25 years.  But, climate change may do more damage to the Earth than all of these other factors.

World Bank Chief Scientist Dr. Robert Watson says, "It may become the most dominant threat to ecological systems over the next hundred years.  We've clearly got to reduce greenhouse gas emissions, change our energy policies, use our energy more wisely."

Dr. Robert Watson

Dr. Watson says the future is bleak, unless dramatic steps are taken.  He says governments need to eliminate subsidies in agriculture, transportation, and energy that lead to environmental degradation.

"We can develop technologies for much more sustainable agriculture, sustainable energy, and we can use technology also to restore our ecosystem," says Dr. Watson.

The report says unless changes are made - efforts to address hunger, poverty and improve healthcare will be compromised.