Planetary boundaries

Planetary boundaries is a concept involving Earth system processes which contain environmental boundaries, proposed in 2009 by a group of Earth system and environmental scientists led by Johan Rockström from the Stockholm Resilience Centre and Will Steffen from the Australian National University. The group suggested that if human activity pushes the Earth system beyond these boundaries, there is a risk of "irreversible and abrupt environmental change". The concept evolved from an idea regarding the Holocene epoch, the relatively stable period of the last 11,700 years during which all human civilizations have developed.

Concept

The concept of planetary boundaries is based on the understanding that human actions can have disastrous impacts on Earth's ecosystem. The scientists identified nine planetary boundaries within which humanity can continue to develop and thrive for generations to come. Crossing these boundaries could generate abrupt or irreversible environmental changes. The nine boundaries are climate change, ocean acidification, stratospheric ozone depletion, nitrogen and phosphorus cycles, global freshwater use, change in land use, biodiversity loss, atmospheric aerosol loading, and chemical pollution.

Planetary Boundaries

Climate Change

Climate change is one of the most critical planetary boundaries. It refers to the long-term alteration in average weather patterns, especially a rise in global temperatures. The boundary is defined by the concentration of carbon dioxide in the atmosphere and the change in average global surface temperature.

Ocean Acidification

Ocean acidification is a decrease in the pH of the Earth's oceans, caused by the uptake of carbon dioxide from the atmosphere. This process makes the ocean more acidic, which can harm marine life, particularly organisms with calcium carbonate shells.

Stratospheric Ozone Depletion

Stratospheric ozone depletion is the reduction of ozone in the stratosphere due to the release of ozone-depleting substances. The boundary is defined by the concentration of ozone-depleting substances in the stratosphere and the size of the Antarctic ozone hole.

Nitrogen and Phosphorus Cycles

The nitrogen cycle and the phosphorus cycle are two of the most important nutrient cycles in terrestrial ecosystems. They are essential for the production of amino acids and nucleic acids, which are the building blocks of life. The boundary is defined by the amount of nitrogen removed from the atmosphere for human use and the quantity of phosphorus flowing into the oceans.

Global Freshwater Use

Global freshwater use refers to the total volume of water used by humans from freshwater sources. The boundary is defined by the global consumption of freshwater.

Change in Land Use

Change in land use involves the alteration of the purpose for which land is used by humans. The boundary is defined by the percentage of global forest cover.

Biodiversity Loss

Biodiversity loss is the decrease in the variety of life forms on Earth. The boundary is defined by the extinction rate.

Atmospheric Aerosol Loading

Atmospheric aerosol loading refers to the amount of solid particles or liquid droplets suspended in the air. The boundary is defined by the overall effect of aerosols on the Earth's climate system.

Chemical Pollution

Chemical pollution involves the introduction of harmful substances into the environment. The boundary is defined by the concentration of pollutants, plastics, heavy metals, and radioactive substances in the environment.

See Also

• Anthropocene
• Earth system science
• Global change
• Sustainability