9.5 Global Climate Change

Rising CO2 and the greenhouse effect

Human activities, especially fossil fuel combustion and deforestation, have raised atmospheric CO2 concentrations dramatically since the Industrial Revolution. CO2, along with methane and other greenhouse gases, traps outgoing infrared radiation, enhancing the natural greenhouse effect and causing global average temperatures to rise — a phenomenon called global climate change.

Evidence for climate change

Scientists use multiple lines of evidence: ice cores (trapped air bubbles show past CO2/temperature), tree rings, ocean sediment layers, rising sea levels, shrinking glaciers and ice sheets, and direct atmospheric measurements (e.g., the Keeling Curve). These independent data sets consistently show warming trends correlated with rising greenhouse gas levels.

Consequences of a warming planet

Climate change causes sea level rise (thermal expansion + melting ice), more frequent/intense extreme weather events, shifting species ranges and phenology, ocean acidification, coral bleaching, and disruption of agriculture and water supplies. These impacts threaten biodiversity, food security, and human health worldwide, especially in vulnerable coastal and low-income regions.

Key terms

Greenhouse effect

Natural process where gases like CO2 and methane trap infrared radiation, warming Earth's atmosphere; human activity has intensified it.

Keeling Curve

A graph showing the continuous rise in atmospheric CO2 concentration measured at Mauna Loa since 1958.

Ice cores

Cylindrical samples of ice containing trapped air bubbles used to reconstruct past atmospheric composition and temperature.

Ocean acidification

Decrease in ocean pH caused by CO2 dissolving into seawater, harming calcifying organisms like corals and shellfish.

Sea level rise causes

Thermal expansion of ocean water and melting glaciers/ice sheets due to global warming.

Try an AP-style question

What is the main driver of recent global warming?

1. Increased solar output
2. Volcanic eruptions
3. Rising CO₂ from fossil fuels
4. Ozone layer depletion