source 1 sum. synthesis

Greenhouse Gases

• Gases in the atmosphere that absorb and re-emit solar energy.
• Key greenhouse gases:
  • Carbon dioxide (CO2)
  • Methane (CH4)
  • Water vapor (H2O)
  • Ozone (O3)
  • Nitrous oxide (N2O)
  • Chlorofluorocarbons (CFCs)

Greenhouse Effect

• Process that traps warmth from sunlight in Earth's atmosphere.
• Essential for maintaining life by keeping temperatures higher than they would be otherwise.

Carbon Dioxide (CO2)

• Major greenhouse gas, responsible for ~74% of emissions.
• Average atmospheric lifetime of ~12 years.
• Accumulated due to industrial activities since the Industrial Revolution.
• Levels increased from 315 ppm (1960) to 419 ppm (2023).
• Historical emissions primarily from the U.S. and Europe, now dominated by China and Asia.

Water Vapor (H2O)

• Natural greenhouse gas; contributes to the greenhouse effect.
• Increased levels linked to rising global temperatures.

Methane (CH4)

• Accounts for ~17% of emissions; potent greenhouse gas (30 times more effective than CO2 over 100 years).
• Concentration has risen by 150% since 1750.
• Natural and human sources: wetlands, livestock, landfills, fossil fuel extraction.

Other Greenhouse Gases

• Ozone (O3) and nitrous oxide (N2O) are significant but less abundant.
• N2O is 265 times more effective than CO2 over 100 years, lasting about 121 years in the atmosphere.
• CFCs used in refrigeration and aerosol propellants, contributing to warming.

Global Emissions Overview

• U.S. greenhouse emissions decreased by 20% (2005-2020); global emissions increased by 43% (1990-2015).
• Main sources of emissions:
  • Transportation, electricity (75%)
  • Agriculture (10%)
  • Commercial/residential (13%)
• China and U.S. are top emitters; low per-capita emissions in some sub-Saharan countries.