Science & Technology

To Keep Thriving, Earth Must Stay Within These 9 Planetary Boundaries

A long, long time ago, back when Earth was emerging from its last ice age and humans still hunted giant sloths, life was good. The environment was stable, and it gave our species a chance to rise, develop civilization, and invent amazing things like science and poetry and grapefruit spoons. But all that ingenuity is now leaving a mark on the planet, and it's making the future of our species uncertain. In 2009, an international group of scientists got together to determine just how bad the situation is. The answer? Things aren't great, but if we stay within their nine guidelines, there might still be hope.

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Out of Bounds

You can think of the nine planetary boundaries devised in 2009 by Johan Rockström, director of the Stockholm Resilience Centre, and 28 other scientists as a kind of health checklist for Earth. Just as your doctor checks your weight, blood pressure, and cholesterol to see if they match what public health researchers have agreed are healthy levels, these planetary boundaries are benchmarks that can let us know the health of our planet. If we stay within them, the scientists say, we can go on thriving for generations to come. If we don't, the results could be catastrophic. Even violating a single boundary can be enough to throw off the environmental balance, since many of the boundaries are dependent on each other — for example, the way rising CO2 levels contribute both to the warming of the planet and the acidification of the oceans.

So what are these boundaries, and how are we doing on each of them? We've listed all nine below, followed by whether we've crossed them (noted by "high risk"), we're approaching them ("increasing risk"), or we're a good distance away from reaching them ("safe").

Climate Change (High Risk)

Boundary: Atmospheric CO2 at 350 parts per million and 1-watt change in radiative forcing

Current status: Atmospheric CO2 at 398 parts per million and 2.3-watt change in radiative forcing

At this point, we all know that climate change is a big problem. According to the researchers, surpassing the boundaries they set — which, of course, we already have — "will increase the risk of irreversible climate change, such as the loss of major ice sheets, accelerated sea-level rise and abrupt shifts in forest and agricultural systems." Unfortunately, we're already seeing this in action: Ice sheets and glaciers are retreating and the sea levels are rising.

Biodiversity Loss (High Risk)

Boundary: Annual loss of 10 species per million

Current status: Annual loss of more than 100 species per million

No species goes on living forever (just ask the dinosaurs), but humanity is definitely not helping the situation. Over every year of our planet's history, species have gone extinct at a rate of roughly 0.5 species per million. Today, it's between 100 and 1,000 times that amount. The researchers say the main culprit behind this our tendency to turn natural ecosystems into cities or farmland — that is, "land use," which is another boundary on this list.

Biochemical Flows (High Risk/Increasing Risk)

Boundary: 35 million tonnes of nitrogen removed from the atmosphere and 11 million tonnes of phosphorus flowing into the ocean annually

Current status: 150 million tonnes of nitrogen removed from the atmosphere and 22 million tonnes of phosphorus flowing into the ocean annually

Nitrogen and phosphorus are naturally occurring minerals that are essential for plant growth. Around the turn of the 20th century, farmers figured out that they could vastly increase their crop yields — and prevent millions from starving, as a result — by adding extra nitrogen and phosphorus to the soil. Unfortunately, what's good for eating isn't good for the environment, and when these minerals end up in the waterways they can deplete oxygen levels and harm fish populations. We're far beyond the nitrogen boundary, and phosphorus isn't doing too hot either.

Ozone Depletion (Safe)

Boundary: 5 percent reduction from pre-industrial levels

Current status: Safe; only transgressed over Antarctica seasonally

Good news, everyone! While we once had a gaping hole in the ozone layer, the global ban of chlorofluorocarbons (CFCs) in 1987 has helped it bounce back. At this rate, scientists think it could be completely healed by 2060.

Ocean Acidification (Increasing Risk)

Boundary: At least 80 percent of pre-industrial aragonite saturation in surface seawater

Current status: 84 percent of pre-industrial aragonite saturation in surface seawater

Like we mentioned, this boundary is closely tied to climate change and CO2 levels. As CO2 levels in the atmosphere rise, the ocean absorbs a big chunk of it and turns it into carbonic acid. This makes it hard for shellfish to build shells, dissolves coral reefs, and cuts down on the food supply for other sea life. That's why this boundary uses aragonite levels as its main measure: aragonite is a form of calcium carbonate that corals use to build their calcium-based structures.

Freshwater Use (Increasing Risk)

Boundary: 4,000 square kilometers of freshwater consumed annually

Current status: 2,600 square kilometers of freshwater consumed annually

This one's kind of obvious: All life needs fresh water to survive. As a result, our consumption of freshwater has an impact on nearly every other boundary on this list. Without enough water, we lose more species, deplete our forests, and reduce the amount of precipitation, which affects the climate. We're doing okay on this boundary — for now.

Land Use (Increasing Risk)

Boundary: 75 percent of potential forest cover converted to other land

Current status: 62 percent of potential forest cover converted to other land

This category is huge for climate change. The exchange of energy and water between the planet's surface and the atmosphere is deeply dependent on what's on that surface since forests are big, wet energy absorbers. This is why you hear so much about the rainforests — if we lose them, we'll irreversibly harm the climate. This one's still decent, but it's not looking good.

Atmospheric Aerosol Loading (Not Quantified)

Boundary: To be determined

Current status: To be determined

This boundary refers to super-fine particles in the air that come from pollution — stuff like smoke, ozone, and the nitrous oxide produced from nitrogen added to soil. This is obviously bad for humans to breathe, but it also messes with crops and weather. It's the main culprit behind worsening monsoons in Asia, for example. But because aerosols can mean so many different things and play a part in so many different elements, it's hard to put an exact boundary on them.

Chemical Pollution (Not Quantified)

Boundary: To be determined

Current status: To be determined

"Primary types of chemical pollution include radioactive compounds, heavy metals, and a wide range of organic compounds of human origin," write the researchers. It's both directly harmful to humans and other life on Earth, and indirectly harmful through its impact on other boundaries. Unfortunately, there are a lot of toxic chemicals out there, so this boundary is a little too broad to make any hard and fast rules on.

It's easy to feel discouraged when you read about all the ways our planet could be doomed, but it's not all bad. What's measured gets managed, as they say, and having precise boundaries like these ones makes it easier for experts to keep tabs on how Earth is doing. It's not in the peak of health right now, but there are ways to help it heal.

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Written by Ashley Hamer November 28, 2018

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