W4 Environmental Policy and Solar Geoengineering Practice Flashcards

This set covers vocabulary and quantitative benchmarks for the nine planetary boundaries, the mechanics of atmospheric aerosols, and the ethical-political debates surrounding solar geoengineering.

Solar Geoengineering (SG)

Methods used to ameliorate climate hazards due to long-lived greenhouse gases (GHGs) by modifying the radiative forcing of climate, primarily by reducing the absorbed solar flux.

Stratospheric Aerosol Injection (SAI)

A solar geoengineering strategy involving the injection of tiny aerosol particles, such as sulfur, into the upper atmosphere to reflect sunlight and lead to cooling.

Planetary Boundaries Framework

A scientific framework identifying nine processes critical for maintaining the stability and resilience of the Earth system as a whole.

Holocene

The stable interglacial period of the past $\sim 10,000$ years during which agriculture and modern civilizations evolved, characterized by global mean surface temperature variations within $\pm 0.5^{\circ}\text{C}$.

Anthropocene

The proposed epoch in which human activities have moved the Earth system outside of the Holocene's window of environmental variability.

Net Primary Production (NPP)

A computable proxy for photosynthetic energy and materials flow into the biosphere; the preindustrial global terrestrial value is determined to be $55.9 \times 10^9\,\text{t C year}^{-1}$.

Human Appropriation of Net Primary Production (HANPP)

The control variable for functional biosphere integrity, measuring the fraction of potential natural NPP harvested or eliminated by human activity; the boundary is set at $10\%$ of preindustrial Holocene mean NPP.

E/MSY

Extinctions per million species-years; the control variable for the genetic diversity component of biosphere integrity, with a boundary set at $<10\,\text{E/MSY}$.

Radiative Forcing Boundary

The limit for total anthropogenic radiative forcing at the top-of-atmosphere set at $+1.0\,\text{W m}^{-2}$ to maintain a safe operating space.

Novel Entities

Anthropogenic introductions to the Earth system that are not naturally occurring, including synthetic chemicals, microplastics, and anthropogenically mobilized radioactive materials.

Aerosol Optical Depth (AOD)

A generic control variable for aerosol loading that provides an integrated measure of the overall reduction in sunlight reaching Earth’s surface caused by absorption and scattering.

Interhemispheric Difference in AOD

The globally defined control variable for aerosol loading, with a planetary boundary value of $0.1$ and a current mean annual value of $\sim 0.076 \pm 0.006$.

Termination Shock

The risk of a rapid, catastrophic rise in global temperatures that would occur if a solar geoengineering deployment system were suddenly destroyed or failed.

Moral Hazard (Mitigation Inhibition)

The concern that the deployment or credible possibility of solar geoengineering will cause political actors to slow or unjustly delay emissions cuts.

Noncompliance of the Powerful (NCP)

A background assumption for climate policy reasoning that powerful political actors will continue to advance what they perceive as their own self-interest rather than moral demands.

Cloud Condensation Nuclei (CNN)

Microscopic organic or inorganic particles, such as dust or volcanic ash, that serve as sites around which water vapor condenses to form cloud droplets.

Primary Aerosols

Aerosols directly suspended in the atmosphere, including inorganic components like sea salt and dust ($>1\,\mu\text{m}$) and organic components like black carbon ($<1\,\mu\text{m}$).

Secondary Aerosols

Particles produced from atmospheric gases interacting with vapor, such as sulfates and nitrates, ranging in size from $nm$ to $1\,\mu\text{m}$.

Albedo

A dimensionless measure of energy reflected at a surface ranging from $0$ to $1$, where snow has a high albedo ($0.8$) and forests have a low albedo ($0.1$).

Ocean Acidification Boundary

Defined by the average global surface ocean saturation state with respect to aragonite ($\Omega_{arag}$), with the boundary set at $\geq 80\%$ of the mean preindustrial value of $3.44\,\Omega_{arag}$.

Biogeochemical Flows Boundary

The limit on human perturbation of global element cycles, currently addressing Nitrogen ($N$) and Phosphorus ($P$) application rates.

Blue Water

Surface and groundwater; the boundary is set at the $95^{\text{th}}$ percentile of preindustrial variability for global land area with streamflow deviations.

Green Water

Plant-available water held in root-zone soil moisture; identified as a separate component of the freshwater change planetary boundary.

Stratospheric Ozone Depletion Boundary

The limit allowing for a $<5\%$ reduction from the preindustrial global average level of $290\,\text{Dobson units (DU)}$.

Cloud Seeding

A form of geoengineering that manipulates existing clouds by spraying aerosol mists, such as salt, to encourage increased rainfall in arid regions.