Planetary Boundaries and Earth System Science

A set of vocabulary flashcards covering the core concepts, specific data, and updated 2023 metrics of the Planetary Boundary framework, based on the three provided sources.

Holocene

A period of environmental stability spanning approximately the last 10,000 years during which human civilizations arose, developed, and thrived.

Anthropocene

A newly proposed geological epoch in which human activities have become the main driver of global environmental change, potentially pushing the Earth system out of the stable Holocene state.

Planetary Boundaries

A framework identifying nine Earth-system processes and associated thresholds that define a safe operating space for humanity with respect to the Earth’s biophysical subsystems.

Resilience

The capacity of Earth’s ecosystems and regulatory systems to dampen disturbances and maintain a stable state.

Thresholds

Critical values for control variables, such as $CO_2$ concentration, which if crossed can cause an Earth subsystem to shift into a new state with potentially disastrous consequences.

Climate Change Boundary

Defined by two parameters: atmospheric carbon dioxide concentration (proposed at $350\,ppm$) and radiative forcing (proposed at $1\,W\,m^{-2}$ above pre-industrial levels).

Radiative Forcing

The rate of energy change per unit area of the globe as measured at the top of the atmosphere, measured in $W\,m^{-2}$.

Biosphere Integrity

A core planetary boundary with two dimensions: genetic diversity (measured by extinction rate) and functional integrity (measured through photosynthetic energy flow).

Genetic Diversity component (Biosphere Integrity)

Measured using the extinction rate; the proposed boundary is $< 10\text{ E/MSY}$ (extinctions per million species-years).

Functional Integrity component (Biosphere Integrity)

A dimension of biosphere integrity quantified by the Human Appropriation of Net Primary Production ($HANPP$).

HANPP (Human Appropriation of Net Primary Production)

A control variable representing the fraction of the biosphere's net primary production ($NPP$) harvested, eliminated, or altered by human activities.

Stratospheric Ozone Depletion

Defined by the concentration of ozone in Dobson Units ($DU$); the boundary allows for a $< 5\%$ reduction from the pre-industrial level of $290\,DU$, currently at $284.6\,DU$.

Ocean Acidification

A process measured by the global mean saturation state of aragonite in surface sea water ($\Omega_{arag}$), with a proposed boundary of $\ge 80\%$ of the pre-industrial mean.

Aragonite ($\Omega_{arag}$)

A form of calcium carbonate used by shell and reef-forming organisms; its saturation state in the surface ocean is currently estimated at $2.8$, down from a pre-industrial value of $3.44$.

Freshwater Change Boundary

Revised in 2023 to include two components: Blue water (surface and groundwater streamflow) and Green water (plant-available soil moisture).

Blue Water

A component of the freshwater cycle representing surface and groundwater flow, used to account for river regulation and aquatic ecosystem integrity.

Green Water

Plant-available water in the root-zone soil, essential for the hydrological regulation of terrestrial ecosystems and climate.

Biogeochemical Flows

A boundary focusing on human interference with the global cycles of nitrogen ($N$) and phosphorus ($P$).

Nitrogen Cycle Boundary

Limited by the amount of reactive $N_2$ removed from the atmosphere for human use; the proposed boundary is $62\,Tg\,N\,year^{-1}$.

Phosphorus Cycle Boundary

Global boundary involves the flow of $P$ from freshwater to oceans, set at $11\,Tg\,P\,year^{-1}$ to avoid large-scale ocean anoxic events.

Land System Change

Measured by the percentage of global land cover converted to cropland or the percentage of original forest area remaining, specifically in tropical, temperate, and boreal biomes.

Atmospheric Aerosol Loading

Defined by overall particulate concentration; the global control variable is the annual mean interhemispheric difference in Aerosol Optical Depth ($AOD$), with a boundary set at $0.1$.

Aerosol Optical Depth ($AOD$)

An integrated measure of the reduction in sunlight reaching Earth’s surface due to absorption and scattering by particles in the air column.

Novel Entities

A planetary boundary for synthetic chemicals and substances not naturally present in the Earth system, including microplastics, endocrine disrupters, organic pollutants, and radioactive materials.

Ecosystem Services

A framework describing the benefits humans receive from nature, categorized into Provisioning (food, water), Regulating (climate control), Supporting (nutrient cycling), and Cultural (aesthetic values).

Provisioning Services

Ecosystem services that provide material outputs like food, timber, cotton, and medicinal herbs.

Regulating Services

Ecosystem services that act as regulators, such as air quality filtering, carbon sequestration, and natural disaster control.

Supporting Services

Necessary for the production of all other services, including soil formation, photosynthesis, and habitat provision.

Scientific Method

A systematic methodical process informed by ideas and principles to create laws and theoretical knowledge through empirical evidence about lived reality.

Empirical Evidence

Information or data based on direct observation or experience rather than purely on theory.