Planetary boundaries are the natural limits on humanity's use of the planet. Strikingly, until recently, no one had made a serious effort to quantify these limits in measurable ways. That's why a new report from the Stockholm Resilience Center, attempting to give hard numbers for most of these boundaries, is so crucial.
The Resilience Center focused in on nine boundaries: climate change, stratospheric ozone, land use change, freshwater use, biological diversity, ocean acidification, nitrogen and phosphorus inputs to the biosphere and oceans, aerosol loading and chemical pollution. These are each critical in their own ways:
Stratospheric ozone layer The stratospheric ozone layer filters out ultraviolet radiation from the sun. (Find more on the stratospheric ozone layer in our archives: Aura.)Biodiversity
"In the Millennium Ecosystem Assessment of 2005, it was concluded that changes in biodiversity due to human activities were more rapid in the past 50 years than at any time in human history..."
(Find more on biodiversity in our archives: Millennium Ecosystem Assessment Scenarios.)Chemicals dispersion
"Emissions of persistent toxic compounds such as metals, various organic compounds and radionuclides, represent some of the key human-driven changes to the planetary environment. [Their] effects are potentially irreversible. Of most concern are the effects of reduced fertility and especially the potential of permanent genetic damage."
(Find more on chemicals dispersion in our archives: Personal Pollution Index.)Climate Change
"We have reached a point at which the loss of summer polar ice is almost certainly irreversible. From the perspective of the Earth as a complex system, this is one example of the sharp threshold above which large feedback mechanisms could drive the Earth system into a much warmer, greenhouse gas-rich state... Recent evidence suggests that the Earth System, now passing 387 ppmv CO2, has already transgressed this Planetary Boundary."
(Find more on Climate Change in our archives: Zero, Now.)
Ocean acidification
"Around a quarter of the CO2 humanity produces is dissolved in the oceans. Here it forms carbonic acid, altering ocean chemistry and decreasing the pH of the surface water. Increased acidity reduces the amount of available carbonate ions, an essential building block used for shell and skeleton formation in organisms such as corals, and some shellfish and plankton species. ...The ocean acidification boundary is a clear example of a boundary which, if transgressed, will involve very large change in marine ecosystems, with ramifications for the whole planet."
(Find more on ocean acidification in our archives: Oceans Are the New Atmosphere.)Freshwater consumption and the global hydrological cycle
"The freshwater cycle is both a major prerequisite for staying within the climate boundary, and is strongly affected by climate change. Human pressure is now the dominating driving force determining the function and distribution of global freshwater systems. The effects are dramatic, including both global-scale river flow change and shifts in vapour flows from land use change."
(Find more on freshwater and the hydrological cycle in our archives: World Water Day: Freshwater Roundup.)Land system change
"Land is converted to human use all over the planet. Forests, wetlands and other vegetation types are converted primarily to agricultural land. This land-use change is one driving force behind reduced biodiversity and has impacts on water flows as well as carbon and other cycles. Land cover change occurs on local and regional scales but when aggregated appears to impact the Earth System on a global scale."
(Find more on land system change in our archives: Protecting the Environment, Protecting Our Health.)Nitrogen and phosphorus inputs to the biosphere and oceans
"Human modification of the nitrogen cycle has been even greater than our modification of the carbon cycle. Human activities now convert more N2 from the atmosphere into reactive forms than all of the Earth´s terrestrial processes combined. Much of this new reactive nitrogen pollutes waterways and coastal zones, is emitted to the atmosphere in various forms, or accumulates in the terrestrial biosphere. ...[Much ends up in] the sea, and can push marine and aquatic systems across thresholds..."
(Find more on nitrogen and phosphorus in our archives: The Nitrogen Wiki.)Atmospheric aerosol loading
"This is considered a planetary boundary for two main reasons: (i) the influence of aerosols on the climate system and (ii) their adverse effects on human health at a regional and global scale."
(Find more on atmospheric aerosol loading in our archives: No Continent is an Island.)
The research has been nicely summarized and presented in a package of articles in Nature, and seems to be generally receiving a very positive reception as an important contribution to the scientific debate.
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