We are on the verge of pushing nature into a state of instability like nothing humanity has seen before, according to a study published in the journal Nature.
The study, which attempted for the first time to come up with real numbers for a set of conditions beyond which Earth may not be able to recover, found that we may have already crossed several tipping points.
"This is all about our health and security," said Jonathon Foley, a climatologist and ecologist at the University of Minnesota, Twin Cities.
"Massive disruptions in climate, ecosystems and so on can have severely negative impacts on things like air quality, pollution levels, pests, emerging diseases and so on."
Excessive global warming, for example, might lead to a rapid rise in sea levels, the collapse of major circulation patterns and drastic changes to regional climates, including more floods and retreating glaciers.
Too much acidification in the oceans, which happens when the seawater absorbs atmospheric carbon dioxide, makes it difficult for creatures to survive, grow and build shells.
Changes in the way we use land and water resources can turn clear blue lakes into murky green ones, harming wildlife, including the fish we eat.
It's as if humanity is driving a car on top of a mesa with the lights off, said Foley. Stepping on the gas in any direction will send us off a cliff.
"Major disruptions in the environment — such as a hurricane or major drought — can be hugely disruptive to people," added Foley, "and lead to mass migrations, refugee issues, increased disease, etc."
How far is too far?
Foley teamed up with 27 experts from around the world to take a broad look at what they called Earth's "safe operating space." The researchers defined nine categories of risk within that space, including global warming, ocean acidification and stratospheric ozone levels.
By compiling and analyzing whatever previously published work they could find in their particular areas of expertise, the scientists tried to quantify how far is too far.
Their estimates suggest that we have already pushed the planet too hard in at least three ways.
The climate researchers, for example, determined that nature will remain in balance only as long as carbon dioxide concentrations in the atmosphere remain below 350 parts per million, yet CO2 concentrations currently measure about 387 parts per million.
"What we're talking about here is truly scary in a lot of ways," Foley told Discovery News. "We're talking about changes in the environment at a global scale that would change this planet into something we have never seen in all of human history. It's not the end of the world, but it's the end of the world as we know it."
Biodiversity researchers, likewise, estimated that species loss is sustainable only if we lose fewer than 10 species for every million on Earth.
However, species are already disappearing at a rate of 100 species per million and projected rates are 10 times higher than that. Nitrogen outputs from chemical fertilizers and other human activities are already threatening to irreparably damage freshwater and marine ecosystems.
‘All of this stuff is hitting the fan’
We are also dangerously close to the thresholds for freshwater use, ocean acidification, and the conversion of forests and other ecosystems into farms and cities. Crossing those lines may lead to a cycle of global catastrophic change.
"Again and again, we find that a little environmental damage is OK," Foley said, but at some point, the planet just can't take it anymore, which is especially true when it's taking multiple hits at once. "In science, we look at one issue at a time. In the real world, all of this stuff is hitting the fan at the same time."
The specific numbers in the study remain estimates, said limnologist Steve Carpenter of the University of Wisconsin, Madison, and scientists will likely debate the details of each tipping point for some time.
The important thing for now, he said, is to recognize that nature has hard edges, that we can't just keep abusing the planet forever, and that we know enough now to be very concerned.
"The important contribution of this paper is to point out that the Earth system has guardrails," Carpenter said. "The consequences of driving the Earth system outside the guardrails are beyond human experience, and some of the consequences will be very bad for civilization."
The new report is not all doom and gloom, Foley insisted. If people work hard to come up with innovations and learn to think in more sustainable ways about food, water and energy, he said, it's still possible to bring nature back within its safe operating space.
"The most important lesson from this is that 'wait and see' is a bad environmental policy," Foley said. "We're in real danger of turning this planet into something we won't even recognize. I hope people start to pay attention."
© 2012 Discovery Channel