AP Environmental Science Unit 9 Climate Change: Mechanisms, Evidence, and Ocean Impacts

Greenhouse effect

A natural process in which certain atmospheric gases absorb and re-emit outgoing infrared (heat) radiation, warming Earth’s surface and lower atmosphere; it makes Earth habitable.

Infrared (IR) radiation

Longer-wavelength radiation emitted by Earth’s surface after it absorbs solar energy; the main form of outgoing heat energy that greenhouse gases absorb.

Albedo

The reflectivity of a surface (or Earth system); higher albedo (e.g., ice, clouds) reflects more incoming solar radiation back to space.

Greenhouse gas (GHG)

An atmospheric gas that absorbs specific wavelengths of outgoing infrared radiation and re-emits it, affecting Earth’s energy balance and temperature.

Enhanced greenhouse effect

Additional warming caused by human-driven increases in greenhouse gas concentrations, strengthening the natural greenhouse effect.

Carbon dioxide (CO2)

A greenhouse gas emitted mainly by fossil fuel combustion, deforestation/land-use change, and cement production; the largest human-driven contributor by total impact due to high emissions and long-lasting effects.

Methane (CH4)

A potent greenhouse gas released from oil and gas systems, landfills, wetlands, livestock digestion, and rice paddies; more effective per molecule than CO2 but generally shorter-lived.

Nitrous oxide (N2O)

A strong greenhouse gas linked especially to agricultural soils through nitrogen fertilizer use and manure management, plus some industrial processes.

Water vapor feedback

A climate feedback where warming allows air to hold more water vapor, which then strengthens the greenhouse effect; water vapor is abundant but mainly acts as a feedback, not the initial driver of recent warming.

Halocarbons

Industrial gases (including CFCs and other refrigerants) that can be very potent greenhouse gases; some also contribute to stratospheric ozone depletion.

Chlorofluorocarbons (CFCs)

A type of halocarbon once used in refrigerants and aerosols; potent greenhouse gases that also cause stratospheric ozone depletion.

Ozone depletion

The thinning of stratospheric ozone (the “ozone hole”) mainly due to chemicals like CFCs; a separate phenomenon from the greenhouse effect and not the primary cause of global warming.

Carbon sink

A reservoir (e.g., ocean or terrestrial ecosystems) that absorbs more carbon than it releases over a time period; sinks can weaken or saturate and are not unlimited.

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

A positive feedback in which melting ice/snow lowers albedo, increasing solar absorption and causing additional warming that leads to more melting.

Permafrost thaw

Warming-driven thawing of frozen soils that can release CO2 and methane from previously frozen organic matter, potentially amplifying warming.

Global climate change

Long-term changes (decades or longer) in Earth’s climate system, including temperature, precipitation patterns, and storm behavior—not just warming alone.

Weather

Day-to-day atmospheric conditions and short-term variability (e.g., today’s temperature or rainfall).

Climate

The long-term pattern and average of weather conditions over many years/decades.

Mitigation

Actions that reduce greenhouse gas emissions or increase carbon uptake to limit future climate change (e.g., renewables, efficiency, reforestation).

Adaptation

Actions that reduce harm from climate impacts and increase resilience (e.g., sea walls, drought-resistant crops, heat emergency planning).

Thermal expansion

The increase in seawater volume as it warms, which raises sea level even without adding water from melting ice.

Stratification (ocean)

Layering in the ocean caused by differences in density (often strengthened by surface warming), which can reduce vertical mixing of oxygen and nutrients.

Coral bleaching

A stress response in which corals under prolonged heat expel their symbiotic algae, turning pale; corals may survive but are weakened and can die if stress continues.

Ocean acidification

A decrease in average ocean pH mainly because the ocean absorbs atmospheric CO2; dissolved CO2 forms carbonic acid and increases hydrogen ions, reducing carbonate availability for shell/skeleton building.