9.4 Increases in the Greenhouse Gases

Human sources boost greenhouse gases

Since the Industrial Revolution, human activities have raised atmospheric concentrations of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor. Burning fossil fuels for energy and transportation releases CO2; agriculture and livestock produce methane and nitrous oxide; deforestation reduces carbon sinks, adding even more CO2 to the atmosphere.

Not all gases are equal

Global warming potential (GWP) compares how much heat a gas traps relative to CO2 over time. Methane has a GWP roughly 25-30 times greater than CO2, and nitrous oxide's is even higher (~270-300x), though CO2's abundance makes it the largest overall contributor. CFCs, once used as refrigerants, are both potent greenhouse gases and ozone destroyers.

Measuring the trend

The Keeling Curve, based on measurements at Mauna Loa Observatory, shows a steady rise in atmospheric CO2 since 1958, along with seasonal fluctuations from plant growth cycles. Ice cores provide historical data showing current CO2 levels are far higher than any point in the past 800,000 years.

Key terms

Global warming potential (GWP)

A measure of how much heat a greenhouse gas traps relative to CO2 over a specific time period.

Keeling Curve

A graph of continuous CO2 measurements from Mauna Loa Observatory since 1958, showing a steady rise with seasonal fluctuations.

Major sources of methane

Livestock (enteric fermentation), rice paddies, landfills, and natural gas leaks.

Role of deforestation in climate change

Removes carbon sinks (trees) and releases stored carbon, increasing atmospheric CO2.

CFCs (chlorofluorocarbons)

Human-made chemicals once used as refrigerants; potent greenhouse gases that also deplete the ozone layer.

Try an AP-style question

What does the Keeling Curve show?

1. Sea level changes over the century
2. Ozone depletion in the stratosphere
3. Steadily rising CO₂ since the 1950s
4. Yearly rainfall patterns worldwide