Humans threaten 4 of 9 key systems on Earth


Human activity dangerously compromises four of the nine systems that are key to maintaining the stability of Earth, report researchers.

The study establishes planetary boundaries—thresholds beyond which there will be irreversible and abrupt environmental change. Those nine boundaries are:

  1. Climate change
  2. Change in biosphere integrity, meaning biodiversity loss and species extinction
  3. Land-system change, such as deforestation
  4. Biogeochemical flows, meaning phosphorus and nitrogen cycles
  5. Stratospheric ozone depletion
  6. Ocean acidification
  7. Freshwater use
  8. Atmospheric aerosol loading, which refers to microscopic particles in the atmosphere that affect climate and living organisms
  9. Introduction of novel entities, for example: organic pollutants, radioactive materials, nanomaterials, and micro-plastics

Earth’s boundaries

The study suggests that changes to the first four items on the list above represent a risk for current and future societies.

Crossing these boundaries raises the risks to current and future societies of destabilizing the Earth System—the complex interactions of land, ocean, atmosphere, ice sheets, life, and people.

The study, published in Science, also reports that significantly altering the first two “core boundaries” on the list—climate change and biosphere integrity—would “drive the Earth System into a new state.”

The internationally agreed upon upper climate limit of 2 degrees Celsius lies beyond that climate change boundary. This makes 2 degrees a risky target for humanity, and therefore an absolute minimum target for global climate negotiations, according to the researchers.

Water and food

Number four on the list, the nitrogen-phosphorus cycle, affecting both the water we drink and our ability to produce food, is seriously compromised.

“People depend on food, and food production depends on clean water,” says Professor Elena Bennett from McGill University’s School of the Environment. She contributed the research on the nitrogen-phosphorus cycle to the study.

“This new data shows that our ability both to produce sufficient food in the future and to have clean water to drink and to swim in are at risk.”

There are two issues relating to the state of the phosphorus-nitrogen cycle. Both elements are essential to plant and animal life. But one of the problems is that phosphorus, which is used as a fertilizer for fields and lawns is in limited supply, and that supply is geopolitically concentrated.

Nearly 90 percent of all known phosphorus reserves are found in just three countries—the vast majority is in Morocco, with China and Algeria coming in next.

The second issue is that the excess of phosphorus-based fertilizers that drain from fields and lawns into neighboring lakes can have disastrous effects on the surrounding water.


It can lead to the sudden growth of algae that can cause the decline or death of other lake organisms and produce toxins that are dangerous to people or animals that swim in the lake or get drinking water from it.

“About half a million residents of the city of Toledo found out that their tap water had been contaminated with a toxin called microcystin last summer. And in 2007 the Quebec government declared that more than 75 lakes were affected by toxins produced by blue-green algae, says Bennett.

“This kind of problem is likely to become much more common. We will see more lakes closed, will have to pay more to clean our water, and we will face temporary situations where our water is not cleanable or drinkable more and more frequently.

“That’s what it means to have crossed this planetary boundary. It’s not a good thing for any of us.”

Source: McGill University