Unit 9: Global Change

Global change

Large-scale shifts in Earth’s climate system and atmosphere over decades to centuries that affect ecosystems, resources, and societies worldwide.

Climate change

Long-term changes in Earth’s climate, driven largely by increasing greenhouse gas concentrations that alter Earth’s energy balance.

Stratospheric ozone depletion

Thinning of protective ozone in the stratosphere caused mainly by human-made chemicals (e.g., CFCs, halons) that catalytically destroy ozone.

Shortwave solar radiation

Incoming energy from the Sun, mainly visible and ultraviolet wavelengths, that reaches Earth.

Longwave (infrared) radiation

Heat energy emitted by Earth back toward space after the surface/atmosphere warms.

Earth’s energy budget (energy balance)

The balance between solar energy Earth absorbs and the energy Earth emits back to space; imbalances lead to warming or cooling until a new balance is reached.

Albedo

The fraction of incoming solar radiation that is reflected back to space; higher albedo generally cools Earth, lower albedo generally warms Earth.

Greenhouse effect

Natural process in which greenhouse gases absorb outgoing infrared radiation and re-emit it (including back toward the surface), warming the lower atmosphere and surface.

Greenhouse gas (GHG)

A gas that absorbs and re-emits infrared radiation, contributing to warming (e.g., CO2, CH4, N2O, water vapor, fluorinated gases).

Carbon dioxide (CO2)

Key greenhouse gas from fossil fuel combustion, deforestation, and cement production; persists long enough to accumulate and drive long-term warming.

Methane (CH4)

Potent greenhouse gas from livestock digestion, rice paddies, landfills, fossil fuel extraction/transport, and wastewater.

Nitrous oxide (N2O)

Greenhouse gas largely from agricultural soils and nitrogen fertilizer use, manure management, and some industrial sources.

Water vapor feedback

Positive feedback where warming increases evaporation and atmospheric water vapor, strengthening the greenhouse effect and amplifying warming.

Fluorinated gases

Industrial greenhouse gases (e.g., HFCs, PFCs, SF6) used in refrigeration and other processes; strong heat-trappers per molecule.

Black carbon (soot)

Light-absorbing aerosol (not a gas) that warms by absorbing sunlight in the atmosphere and darkening snow/ice, lowering albedo.

Positive feedback loop

A process where an initial change triggers effects that amplify the original change (e.g., warming leading to more warming).

Ice–albedo feedback

Positive feedback where melting ice/snow lowers albedo, increasing solar absorption and causing additional warming and melting.

Permafrost thaw

Warming-driven melting of frozen ground that can damage infrastructure and release greenhouse gases (especially methane) as organic matter decomposes.

Polar amplification

The tendency for high-latitude regions to warm faster than the global average, aided by feedbacks like sea-ice loss and energy transport poleward.

Energy supply sector (emissions)

Greenhouse gas emissions from burning coal, oil, and natural gas for electricity and heat; often the largest global source category.

Deforestation (as a GHG driver)

Land-use change that increases atmospheric CO2 by removing carbon-storing biomass and releasing carbon through burning and decomposition.

Consilience

Agreement among multiple independent lines of evidence that support the same scientific conclusion (used in climate change evidence).

Ocean heat content

Measure of heat stored in the oceans; a powerful indicator of long-term warming because oceans absorb most excess heat in the climate system.

Paleoclimate proxy

Indirect record of past climate conditions, such as ice cores, tree rings, sediment cores, or corals.

Thermal expansion

Sea level rise mechanism in which warming seawater expands, increasing ocean volume.

Melting land ice

Sea level rise mechanism where melting glaciers and ice sheets add water to the ocean (unlike floating sea ice, which has little direct effect).

Ocean acidification

Decrease in ocean pH when atmospheric CO2 dissolves in seawater forming carbonic acid, reducing carbonate availability for corals and shell-formers.

Phenology

Timing of seasonal biological events (e.g., flowering, breeding, migration) that can shift as climate warms.

Environmental justice (in climate context)

Focus on how climate impacts and adaptive capacity are uneven; lower-resource communities often face higher risks and fewer options to adapt.

Adaptation

Actions that reduce harm from climate change impacts (e.g., flood protection, cooling centers), addressing damage rather than emissions.

Mitigation

Actions that reduce the magnitude of future climate change by cutting greenhouse gas emissions or increasing carbon sinks.

Carbon sequestration

Capture and long-term storage of carbon in biomass, soils, or geologic formations to reduce atmospheric CO2.

Carbon sink

A reservoir that absorbs more carbon than it releases (e.g., growing forests, some soils).

Decarbonizing electricity

Reducing CO2 from power generation by shifting to low-carbon sources (renewables, nuclear) and improving energy efficiency.

Electrification (end uses)

Replacing direct fossil-fuel use (vehicles, heating, some industry) with electricity to cut emissions when the grid is low-carbon.

Carbon tax

Policy that charges a fee proportional to carbon content or CO2 emissions to internalize climate externalities and incentivize low-carbon choices.

Cap-and-trade

Policy that sets an emissions cap and allows trading of emissions allowances; the cap limits total emissions and trading reduces costs.

Kyoto Protocol

International climate agreement (entered into force 2005) establishing binding greenhouse gas reduction targets for certain countries.

Paris Agreement

International climate agreement (2016) aiming to keep warming well below 2°C above pre-industrial levels using country-defined emissions plans.

Stratospheric ozone (ozone layer)

High-altitude ozone (mostly 15–40 km) that absorbs much harmful UV radiation, especially UV-B, protecting life on Earth.

Tropospheric ozone

Ground-level ozone; an air pollutant and key component of photochemical smog that harms human lungs and plants.

UVB radiation

Ultraviolet radiation associated with sunburn and skin cancer risk; increases at Earth’s surface when stratospheric ozone decreases.

Chlorofluorocarbons (CFCs)

Stable, human-made chemicals formerly used in aerosols/refrigeration/foams; reach the stratosphere where UV releases chlorine that destroys ozone.

Catalytic ozone destruction

Process where released halogen atoms (chlorine/bromine) destroy ozone through cycles while the halogen is not consumed, enabling many ozone losses.

Polar stratospheric clouds

Clouds that form in extremely cold stratospheric conditions (especially over Antarctica) and promote rapid ozone destruction when sunlight returns in spring.

Montreal Protocol

1987 international treaty that phased out CFCs and other ozone-depleting substances; a major success in addressing ozone depletion.

Managed retreat

Adaptation strategy that relocates infrastructure/development away from high-risk areas (e.g., vulnerable coasts) to reduce long-term exposure.

Invasive species

Non-native organism that spreads in a new area and often causes ecological, economic, or human-health harm.

Endangered species

A species facing a very high risk of extinction in the wild, based on factors like population trends, threats, and number of individuals remaining.

Systems thinking

Approach that analyzes how changes in one part of a system (emissions, atmosphere, climate, ecosystems, society) propagate through linked components and feedbacks.