Atmospheric Composition and Moisture

Carbon Dioxide ( $CO_2$ ): Discussed in relation to the Earth's energy budget.
- Naturally occurs in Earth's atmosphere through surface processes.
- Human activities significantly contribute to atmospheric $CO_2$ through the burning of fossil fuels for industrial, domestic, and commercial purposes.
- This contributes to increased $CO_2$ concentrations, which will be revisited in discussions on Earth's energy budget.

Mechanism:
- Longwave energy (thermal infrared radiation) radiated from the Earth's surface.
- This energy gets trapped by greenhouse gases in the atmosphere.
- It is then reradiated back down to the surface.
- This re-radiation of absorbed heat helps keep the Earth's atmosphere warmer than it would be otherwise.
Global Energy Budget Component: The natural greenhouse effect is a crucial element of the global energy budget.
Process Overview:
- Incoming shortwave solar radiation is absorbed by the Earth's surface.
- This energy is reradiated as longwave radiation, also known as thermal infrared radiation.
- Longwave radiation is absorbed by greenhouse gases in the atmosphere.
- Some heat escapes to space, but a significant portion is reradiated back down to the surface.
Significance:
- Keeps Earth's atmosphere significantly warmer. The average temperature on Earth is about $15 ext{ degrees Celsius}$ ( $59 ext{ degrees Fahrenheit}$ ) warmer due to greenhouse gases.
- Without the naturally occurring greenhouse effect, Earth's temperature would be sub-zero year-round (e.g., in La Crosse), making it unsuitable for life and crop growth.

All these gases are variable gases, meaning their concentrations change over space and time.
Water Vapor ( $H_2O$ ):
- The # $1$ most abundant naturally occurring greenhouse gas in the atmosphere.
- Humans do not create or destroy water vapor; it is a naturally occurring atmospheric component.
- Its concentration is higher in tropical oceans and lower in colder temperatures (e.g., La Crosse in winter).
- The amount of water vapor in the air is directly related to air temperature; warmer air can hold more moisture.
Carbon Dioxide ( $CO_2$ ):
- As discussed, humans promote higher concentrations through the burning of fossil fuels, releasing fossilized carbon into the atmosphere.
Methane ( $CH_4$ ):
- A naturally occurring greenhouse gas with various sources.
- One significant source is permafrost, where methane is stored.
- Under anaerobic conditions (without oxygen), methanogens release methane gas to the atmosphere.
- Permafrost thawing can release stored methane, while peatlands can act as sinks or sources.
Nitrous Oxide ( $N_2O$ ): Also an important naturally occurring greenhouse gas.

Definition: Tiny particles that remain suspended in the air, originating from both natural processes and human activities.
Sources:
- Dust: Generated by major dust storms over deserts (e.g., Sahara Desert, Patagonia region) where strong winds pick up minute particles.
- Volcanic Eruptions: Eject vast amounts of steam and ash into the atmosphere.
  - The height of the ash plume depends on the eruption's power.
  - Tiny particles from volcanic ash can remain suspended in the air.
- Fossil Fuel Burning:
  - Coal: The