We've been warned. Again.

Because of a dangerous combination of climate change, pollution, mass extinctions and a growing human population, a massive report from the United Nations released Wednesday said that "damage to the planet is so dire that people’s health will be increasingly threatened unless urgent action is taken."

Already, about 25 percent of all premature deaths and diseases around the world – about 9 million in 2015 – are because of human-caused environmental damage and pollution, the report said. Each year, air pollution kills 7 million people worldwide and costs society about $5 trillion. Another 1.4 million are killed because of water pollution.

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The report, the sixth Global Environment Outlook from the U.N. Environment Programme, was written by 250 scientists and experts from more than 70 countries. It concludes that "unsustainable human activities globally have degraded the Earth’s ecosystems, endangering the ecological foundations of society."

Joyce Msuya, acting executive director of U.N. Environment, said “the science is clear. The health and prosperity of humanity is directly tied with the state of our environment."

The report also warned that cities and regions in Asia, the Middle East and Africa could see millions more premature deaths by mid-century. 

"This report is an outlook for humanity," Msuya said. "We are at a crossroads. Do we continue on our current path, which will lead to a bleak future for humankind or do we pivot to a more sustainable development pathway? That is the choice our political leaders must make, now."

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The United Nations warns that the top two environmental concerns are climate change and biodiversity: In regards to climate change, the report said time is running out to prevent its irreversible and dangerous impacts as global temperatures continue to rise. 

As for biodiversity loss, the report said "a major species extinction event, compromising planetary integrity and Earth’s capacity to meet human needs, is unfolding." This threatens ecosystems, fisheries and other major systems.

In addition to pollution, other concerns are antimicrobial resistant bacteria in water supplies and also land degradation that threatens farming and agriculture.

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The report is “a dramatic warning and a high-level road map for what must be done to prevent widespread disruption and even irreversible destruction of planetary life-support systems,” said University of Michigan environment dean Jonathan Overpeck, who wasn’t part of the report.

But all hope is not lost: “There is every reason to be hopeful,” report co-editors Joyeeta Gupta and Paul Ekins said. “There is still time, but the window is closing fast.”

The report was released Wednesday at a U.N. conference in Nairobi, Kenya. 

Contributing: The Associated Press

Appeared first in USA Today.