Sustainable Living & Sustainable Lifestyle

The planetary boundaries theory holds that human activity has driven climate change since the Industrial Revolution that is pushing Earth’s limits in nine key areas

What Are Planetary Boundaries and how have we crossed them?

The planetary boundaries theory holds that human activity has driven climate change since the Industrial Revolution that is pushing Earth’s limits in nine key areas

Scientists built the 21st century theory called planetary boundaries on the idea that since the Industrial Revolution, man has become the main driver of global climate change. It also describes nine key areas where the environment must stay within certain boundaries for mankind to continue to thrive.

The planetary boundaries theory provides both a warning and guidance for mankind. Developed in 2009 by Earth system and environmental scientists, the theory identifies a safe operating space for humanity in nine key areas.

The Stockholm Resilience Centre at Stockholm University provided a home for the international study. The following summarizes what scientists came up with in their theory.

The Theory of Planetary Boundaries

Stockholm Resilience Centre Director Johan Rockström led the international group of 28 scientists to identify nine processes that “regulate the stability and resilience of the Earth system.” The scientists eventually proposed quantitative planetary boundaries. By staying within those boundaries, humanity can continue to safely develop.

On the other hand, if humanity crosses those boundaries, they increase the risk of generating abrupt and/or irreversible environmental changes on a large scale. In short, the planet has limits in certain areas. The theory defines those areas.

Earth’s environmental systems are complex. Because of that, scientists did not seek to establish an exact threshold for crossing the boundary. Rather, they defined a range. The lower end of that range marks the boundary. Once humanity crosses a boundary, we enter into a danger zone.

In 2015, the centre released an update saying that humanity has crossed four of the nine boundaries. Those planetary boundaries are as follows.

The Planetary Boundaries We’ve Crossed

In these four areas, according to scientists, humanity has crossed the boundary into the danger zone.

Loss of Biosphere Integrity

In the Millennium Ecosystem Assessment of 2005, researchers concluded that changes to the ecosystem had accelerated in the preceding 50 years at rate higher than at any point in human history. The result is an alarming high rate of extinction among animal and plant species.

Climate Change

While most people associate climate change with increasing instances of destructive weather, the Earth also has moved past several signposts that indicate it’s in a danger zone. For example, researchers wrote that “we have reached a point at which the loss of summer polar sea-ice is almost certainly irreversible.”

In July 2021, NASA reported that the Earth had reached 417 parts per million of carbon dioxide in the atmosphere, beyond the 350 boundary and far beyond the pre-Industrial Age level of 280. To put that in perspective, NASA reports that carbon dioxide levels between 1850 and 2021 increased more than in the 20,000 years preceding 1850.

“A major question is how long we can remain over this boundary before large, irreversible changes become unavoidable,”  the Stockholm Resilience Centre  wrote.

Nitrogen and Phosphorus Flows to the Biosphere and Oceans

Industrial and agricultural processes have changed biogeochemical cycles of nitrogen and phosphorus, which are both vital for plant growth. Scientists say humans now convert more atmospheric nitrogen into reactive forms than any other process on Earth, much of it emitted into the atmosphere. It also pollutes waterways and coastal zones. The current rate is roughly four times the lower boundary level.

Land System Change

Land system changes primarily involve conversion of forests, grasslands and wetlands into land for farming. In addition to impacting biodiversity, it also changes water flows and can alter the cycles of carbon, nitrogen and phosphorus.  The elimination of large swaths of forested area is especially damaging.

The Planetary Boundaries Not Yet Crossed

These boundaries have not yet been crossed, although in some cases humanity is coming very close to moving into the danger zone.

Stratospheric Ozone Depletion

The atmosphere’s stratospheric ozone layer filters out ultraviolet (UV) radiation from the sun. A decrease in the layer increases the amount of UV radiation reaching the ground, leading to higher rates of skin cancer and widespread damage to both marine and terrestrial biological systems. A hole in the ozone over the Antarctic proved this boundary was being tested, but after actions taken based on the Montreal Protocol, humanity seems on a path to stay within this boundary.

Ocean Acidification

About 25 percent of all carbon dioxide ejected into the atmosphere ends up dissolved in the ocean, where it forms carbonic acid that alters ocean chemistry and decreases the pH of surface water. This causes a loss of species in the ocean, including coral, shellfish and plankton, among others.

Freshwater Consumption

This intensity of the long-lasting droughts in the American West show how freshwater consumption can quickly become an issue. Constant human intervention and alteration of waterways cause changes in the hydrological system. But with an estimated half a billion people facing some form of water stress by 2050, more intervention in water systems is expected with untold consequences.

Atmospheric Aerosols

Aerosols play an important role in many Earth systems. For example, they influence the hydrological cycles that impact everything from cloud formation to monsoon systems. They also play a role in how much solar radiation is absorbed or reflected off the planet. Pollutants and land-use changes can impact aerosols and lead to adverse effects on people through the very air they breathe.

Introduction of Novel Entities

This involves creation of chemical pollutants that are harmful to natural systems, including organic pollutants, radioactive materials, nanomaterials, and microplastics.

These planetary boundaries are receiving an increased amount of attention as people learn about the dangers of crossing them. They also provide guideposts for political leaders who aspire to set a course that involves sustainability and saves Earth from crossing too many tipping points.

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