Overview
This lecture explains human impacts on global climate, focusing on greenhouse gas emissions, deforestation, aerosols, and the resulting trends in global temperature.
Early Human Impacts on Climate
- Humans have altered the environment for thousands of years, affecting climate through fire use and overgrazing.
- Modified ground cover changes climate factors like surface albedo (reflectivity) and evaporation rates.
Post-Industrial Revolution Effects
- Significant climate change impacts emerged from post-industrial emissions of carbon dioxide (CO₂), other greenhouse gases, and aerosols.
- Industrialization, mainly through fossil fuel burning, greatly increased atmospheric CO₂.
Carbon Dioxide and the Greenhouse Effect
- CO₂ is a minor atmospheric component but traps Earth's outgoing longwave radiation, warming the planet (greenhouse effect).
- Fossil fuel combustion contributed around 80% of U.S. energy use in 2017, releasing large amounts of CO₂.
- The Keeling curve shows a steady rise in atmospheric CO₂ since 1958, with seasonal variations due to plant growth and decay.
- Deforestation, especially in tropical rainforests, adds significant CO₂ through burning and land clearing.
Other Greenhouse Gases
- Methane (CH₄) absorbs radiation 20 times more effectively than CO₂ but is less abundant and oxidizes quickly.
- Methane sources include anaerobic bacteria in wetlands, cattle, rice fields, coal mining, and oil extraction.
- Nitrous oxide (N₂O) is a long-lived greenhouse gas released from nitrogen fertilizers and fossil fuel combustion.
Temperature Trends and Global Warming
- Global temperatures have increased steadily since 1880, with most of the warmest years occurring after 2001.
- Global maps and charts show temperature increases across most regions, particularly since 1950.
Aerosols and Climate
- Aerosols are tiny atmospheric particles from both natural and human sources, mainly burning vegetation and fossil fuels.
- Most aerosols cool the Earth by reflecting sunlight and brightening clouds.
- Black carbon (soot) warms the atmosphere and decreases albedo when deposited on snow/ice.
- Despite some warming effects, the net impact of aerosols is global cooling.
Key Terms & Definitions
- Surface albedo — the reflectivity of Earth's surface, influencing how much sunlight is absorbed.
- Greenhouse effect — warming of Earth due to certain gases trapping outgoing radiation.
- Keeling curve — graph showing rising atmospheric CO₂ from Mauna Loa Observatory data since 1958.
- Aerosols — tiny solid or liquid particles suspended in the atmosphere.
- Black carbon — soot particles from incomplete combustion that absorb heat.
Action Items / Next Steps
- Prepare for next video covering climate system feedback mechanisms.
- Review graphs on CO₂ rise, energy consumption, and global temperature trends.