Study Notes on Greenhouse Gas Emissions

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Greenhouse gases are atmospheric gases that absorb and re-emit energy from the sun.
This process of absorbing and emitting radiation is known as the greenhouse effect.
Common greenhouse gases include:
- Carbon dioxide (CO₂)
- Methane (CH₄)
- Water vapor (H₂O)
- Ozone (O₃)
- Nitrous oxide (N₂O)
- Chlorofluorocarbons (CFCs)

Greenhouse gases are released from both natural sources (like vegetation and water bodies) and human activities such as:
- Industrial processes
- Automobile emissions

The greenhouse effect is crucial for life, as it traps warmth from sunlight in the atmosphere, keeping the Earth warm enough to support life.
Without this effect, Earth's global temperatures would be much lower, making many areas uninhabitable.

The phenomenon resembles a greenhouse used for plant growth, where:
- Light and heat enter through glass
- Heat is retained, preventing escape, thus warming the interior
On Earth, the atmosphere functions like the glass panels—allowing sunlight in but preventing much of the heat from escaping back into space.

The Sun emits various types of radiation (visible light, infrared light, etc.) which:
- Pass through Earth's atmosphere
- Are absorbed by the ground, oceans, and vegetation
- Are re-radiated back into the atmosphere in the form of heat
Greenhouse gases capture this heat, which warms the atmosphere further.

Considered a natural greenhouse gas.
Acts to insulate; cloudy nights retain heat better than clear ones.
Behavior:
- During the day, clouds can block sunlight leading to cooling effects
- Dry regions show extreme temperature changes due to lack of water vapor.
Increased global temperature causes more evaporation, which increases water vapor levels, enhancing the greenhouse effect.

About 74% of greenhouse emissions are CO₂.
It is the primary driver of anthropogenic climate change due to its high prevalence in emissions.
Lifetime: Approximately 12 years in the atmosphere.
Significant emissions stem from:
- Burning fossil fuels (coal, oil, gas)
- Motor vehicle emissions
- Industrial activities
Historical Carbon Emissions Trend:
- Levels increased from 315 ppm in 1960 to 400 ppm in 2015.
- Current levels as of October 2023 are around 419 ppm—the highest in approximately 4.5 million years.
- Emissions distribution changed from 90% from U.S. and Europe in 1900 to a lower share by 2020, with China and Asia becoming predominant sources.

Accounts for 17% of greenhouse emissions.
It has significantly higher global warming potential than CO₂:
- 30 times more effective than CO₂ over 100 years
- 82 times more effective over 20 years
Methane persists in the atmosphere for 15-20 years.
Sources:
- Natural decay in wetlands and permafrost
- Livestock digestion (mainly cattle)
- Human activities contribute to 60% of atmospheric methane.
Current concentration is approximately 1.9 ppm, up 150% since 1750, and methane contributes to about one-fifth of greenhouse heating effects.

Ozone (O₃):
- Emitted from industrial sources and contributes to warming, though in lower concentrations than CO₂.
Nitrous Oxide (N₂O):
- Produced by agricultural processes and industrial emissions, with a warming potential of 265 times that of CO₂ over 100 years and a lifespan of about 121 years in the atmosphere.
Chlorofluorocarbons (CFCs):
- Used in refrigeration, aerosol sprays, and solvents, contributing strongly to atmospheric warming.
Volatile organic compounds (VOCs) impact the photochemistry of ozone and climate.
Aerosols can have cooling or warming effects depending on their properties (light vs. dark particles).

According to the U.S. Environmental Protection Agency (EPA):
- U.S. greenhouse gas emissions decreased by 20% from 2005 to 2020.
Globally, emissions increased by 43% from 1990 to 2015.
Primary contributing sectors in the U.S. include:
- Transportation, electricity generation, and industry (about 75% of emissions)
- Agriculture (approximately 10%)
- Commercial and residential uses (around 13% including air conditioning and appliances).
Countries with the highest emissions:
- United States and China.
- Sub-Saharan African nations such as Chad and Niger exhibit the lowest per-capita emissions.