Nine ways to alter the world

In this Tuesday, Feb. 26, 2008 file photo, charcoal kilns are seen in Tailandia, state of Para, Brazil. Money raised by governments and corporations hasn’t managed to halt the destruction of the world’s rainforests - an area the size of Greece is lost every year. (AP Photo/Renato Chalu, File)

Carbon emissions tend to hog the climate change spotlight, but they aren’t the only — or perhaps even the scariest — way that humans dramatically alter the environment.

According to a team of scientists researching humanity’s impact on the planet, greenhouse gas levels are just one of nine “planetary boundaries” that mark the difference between a familiar earth and an unpredictable, likely less hospitable, new world.

The planetary boundary research has been ongoing for at least five years, but a new paper published last month contains a cautionary update: Four of the nine boundaries have already been crossed.

There is already too much carbon dioxide in the atmosphere — about 50 parts per million to be exact. Most scientists agree that 350 ppm of carbon dioxide would be a safe point, but current levels hover just above 400 ppm and are increasing by as much as 3 ppm annually.

And while carbon dioxide is being added to the air, nitrogen is being taken out. Nitrogen and phosphorous chemical cycles — both of which are crucial to agriculture — have also been altered beyond the proposed acceptable boundary. The risks include decreased land fertility and altered marine ecosystems.

Planetary boundary scientists argue that a natural extinction rate for species would be roughly one extinction for every 1 million surviving species. While the extinction rate is tremendously difficult to accurately determine, the paper’s writers argue that it currently stands somewhere between 100 and 1,000 species per million.

Part of that accelerated extinction rate could result from a dangerous amount of deforestation in the name of logging and farming. Global forest cover is estimated at about 62 percent of the pre-human level. That’s lower than the 75 percent boundary but not yet low enough to qualify as a high risk threat for unmanageable environmental change.

Not all of the report is gloom and doom. Global society collaborated very successfully to heal the ozone layer to well within the safe threshold by banning hydroflourocarbons in the 1990s, for example.

Ocean acidification and freshwater consumption are still at safe levels, too. Two boundaries — atmospheric aerosols and chemical pollution — lack sufficient data to make a scientifically informed statement on global levels.

But while the paper addresses worldwide concerns over the future livability of the planet, coming up with solutions to mitigate mankind’s impact on our home will require a critical mass created by local commitment. After all, some boundaries are likely to be much more important than others in any given community.

Charleston faces a much greater threat from rising sea levels and ocean acidification than Denver, for example.

And since any solutions require trade-offs from businesses, individuals and governments, they have and will continue to generate intense debate.

Everyone should agree, however, that maintaining a habitable, hospitable planet ought to be the defining priority.