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We’ve crossed four of nine planetary boundaries. What does this mean?

Flooded forest in the Amazon

Flooded forest in the Amazon. Photo credit: Rhett A. Butler

  • The Earth has nine Planetary Boundaries that determine the threshold beyond which human impact on Earth’s systems will put society at risk. We’ve already crossed four of these boundaries.
  • Over the past year, Mongabay’s series on planetary boundaries has focused attention on the implications of crossing them.
  • Below are some highlights that cover the consequences of crossing four of those boundaries (and solutions to address them), as well as the looming challenges in preventing humanity from overreaching the boundaries we have yet to cross.

With scientists, advocates and communities across the world making increasingly dire assessments and warnings about the planet’s health, knowing what problems to focus on becomes ever more complex. Over the past year, Mongabay published more than 40 articles under the Planetary Boundaries series to explore the science and status of nine Earth systems that support the conditions humans need to operate safely. The concept was introduced by Johan Rockström of Sweden’s Stockholm Resilience Centre, and can be used to assess where humanity stands in its impact on Earth’s systems and the point at which crossing a threshold puts society at risk.

In addition to these articles, Mongabay’s multimedia coverage included 10 interviews, a podcast, and eight YouTube videos from topics ranging from food security to pandemic response and zoonotic diseases, to how the Montreal Protocol saved us from further intense warming.

Contributor Claire Asher highlights the nine boundaries in this article: climate change, biodiversity loss, ocean acidification, ozone depletion, atmospheric aerosol pollution, freshwater use, biogeochemical flows of nitrogen and phosphorus, land-system change, and release of novel chemicals. We’ve already crossed four of these boundaries. Claire also spoke with Mongabay Newscast host Mike Gaowrecki about these boundaries and solutions to the challenges of addressing them, in a podcast episode that you can listen to here:

Of the boundaries that we still operate within, freshwater use faces challenges to cleanliness and accessibility, which Saul Elbein wrote about in this article. Only 3% of the Earth’s water is freshwater, and two-thirds of that is stored in glaciers, leaving just 1% in rivers and streams or underground. The problem is that as humanity continues to grow (especially in arid urban environments like Los Angeles, Phoenix, or Tripoli), the sources of freshwater we use are being depleted faster than they can be replenished. Much of the water we use, 70%, is for agriculture; industry and consumer products account for another 20%.

Freshwater use is further complicated by more frequent and intense droughts brought on by climate change, so much that by 2025 an estimated 1.8 billion people will be living in areas of water scarcity. We also created an explainer video detailing the challenge and potential solutions here:

Staff features writer John Cannon wrote about the twin climate and biodiversity crises in this June 2021 piece discussing a recent report from the United Nations’ Intergovernmental Panel on Climate Change (IPCC) and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES). The report emphasizes that conserving biodiversity (a planetary boundary we have already passed) is crucial to solving the climate crisis. The authors suggest that in addition to shifting our societies’ energy systems away from dependency on fossil fuels and reducing all sources of greenhouse gas emissions, 30-50% of the world’s landmass must be set aside for conservation.

Of the four Planetary Boundaries humanity has crossed (climate change, biodiversity loss, land-system change, and biogeochemical flows), all of them are tied to the health of the Earth’s soil, which Claire Asher detailed in a piece about conserving soil carbon. Of all the carbon that is stored on land, 80% is contained within soil, and experts suggest that maintaining ancient soil carbon stores could make up one-quarter of the carbon mitigation load. In addition, carbon-rich areas of soil are also often areas of high biodiversity, providing further incentive to conserve these areas and maintain biodiversity. Overhauls to agribusiness have been suggested, such as regulating the use of synthetic fertilizer, restoring degraded land, and changing industrial agricultural practices by switching to agroforestry (which has seen successful implementation in Tajikistan).

Extreme events like a prolonged drought in the Sahel region are causing a massive environmental migration crisis. Image by Pablo Tosco/Oxfam via Flickr [CC BY-NC-ND 2.0]

Further covering the indivisible link between these planetary boundaries, staff writer Elizabeth Claire Alberts highlighted five of Earth’s subsystems that a recent risk analysis found are at risk of destabilizing each other in a “domino effect.” These interconnected tipping points could occur even before reaching the Paris Agreement limit of 2° Celsius (3.6° Fahrenheit) of warming above pre-industrial levels. The West Antarctic Ice Sheet, the Greenland Ice Sheet, the Atlantic Meridional Overturning Circulation (AMOC), the El Niño–Southern Oscillation (ENSO) and the Amazon Rainforest are the five subsystems that could interact with each other in a cascading manner, though the time scale in which this would occur remains unclear.

Conrad Fox wrote more about climate “tipping points” in this article: what constitutes them and how they interact with one another, in addition to other planetary thresholds.

Sir David Attenborough. Image courtesy of the BBC.

Mongabay also profiled David Attenborough and Johan Rockström’s new Netflix film Breaking Boundaries: The Science of Our Planet. The documentary details the planetary boundaries at length and the triggering of irreversible tipping points that Rockstöm says would occur if the Earth surpasses 450 parts per million of carbon dioxide in the atmosphere. Along with further expanding on the other three boundaries we’ve passed, the film also offers clear solutions that come just before three key U.N. summits that will take place in 2021.

Readers can follow Mongabay’s continuing coverage of the planetary boundaries at the Planetary Boundaries series page.

Banner Image: Flooded forest in the Amazon. Photo credit: Rhett A. Butler

Mike DiGirolamo is Mongabay’s audience engagement associate. Find him on Twitter @MikeDiGirolamo, Instagram or TikTok via @midigirolamo.