Planetary Boundaries, Nutrient Pollution and Human Civilization
An international team of researchers published a report in Science on Thursday, finding that humanity has exceeded four out of nine planetary boundaries that constitute a safe operating space for humans. Steve Carpenter, director of the University of Wisconsin-Madison Center for Limnology and the only US-based researcher, defines planetary boundaries as “the outer limits of change to the Earth’s system that we think is tolerable to maintain good conditions for civilization.”
Dr. Carpenter explains the planetary boundaries concept by reviewing the Earth’s history. There was a stable period- the Holocene Period- that lasted from about 11,700 years ago to about 100 years ago, when all of the major civilizations on every continent emerged. Agriculture developed. The Holocene was a good period for civilization. According to Carpenter, “it would be desirable to try to maintain those conditions. It might be possible for civilizations to live outside Holocene conditions, but we don’t know that. It’s never been tried before. We know civilization can make it Holocene conditions, so it seems wise to try to maintain those conditions.”
Humanity has exceeded the boundaries of Holocene conditions, according to the study. While several boundary areas are addressed, Steve Carpenter’s focus in the study is on two elements that are widely used to fertilize crops: nitrogen and phosphorus.
Both are widely used to fertilize crops, and the rise of large-scale, industrial agriculture has led to an immense increase in the amount of the chemicals entering our ecosystems.
“We’ve changed nitrogen and phosphorus cycles vastly more than any other element,” Carpenter says. “(The increase) is on the order of 200 to 300 percent. In contrast, carbon has only been increased 10 to 20 percent and look at all the uproar that has caused in the climate.”
The increase in phosphorus and nitrogen has been especially detrimental to water quality. Phosphorus loading is the leading cause of both harmful algal blooms and the oxygen-starved “dead zone” in Lake Erie. Likewise, nitrogen flowing down the Mississippi River is the main culprit behind the “dead zone” in the Gulf of Mexico.
While nitrogen and phosphorus levels overall are well beyond the Holocene boundaries, Carpenter says the chemical load isn’t spread evenly over the planet.
“There are places that are really, really overloaded with nutrient pollution,” he says. “Wisconsin and the entire Great Lakes region are some of those. But there are other places where billions of people live that are undersupplied with nitrogen and phosphorus.”