1. Greenhouse Effect & Atmospheric Gases

Define Greenhouse Gases

• Greenhouse gases trap heat in the Earth’s atmosphere by absorbing infrared radiation.

• Major greenhouse gases:
  

  • Carbon Dioxide (CO₂) – comes from burning fossil fuels, deforestation.

  • Methane (CH₄) – released from landfills, livestock digestion, and wetlands.

• Why are they effective? They absorb and re-emit infrared radiation, creating a “blanket” that keeps the planet warm — this is called the greenhouse effect.

Volcanic Activity & Earth’s Temperature

• Volcanoes emit ash, aerosols (like sulfur dioxide), and greenhouse gases.
  

  • Short-term effect: Ash and aerosols reflect sunlight, cooling the planet (e.g., Mt. Pinatubo in 1991).

  • Long-term effect: CO₂ emissions from eruptions can increase global temperatures over centuries.

2. Earth’s Tilt, Seasons, and Insolation

Tilt of Earth’s Axis

• Earth is tilted at 23.5°. This tilt is why we have seasons.

• When the Northern Hemisphere tilts toward the Sun → summer there. Away → winter.

If Tilt Increased to 33.5°

• Hotter summers and colder winters (more extreme seasonal differences).

• Longer daylight in summer, shorter in winter.

Heat Equators and Temperature Zones

• The heat equator (Intertropical Convergence Zone) moves with the Sun’s direct rays.

• A change in Earth’s tilt shifts this zone, moving climate zones and weather patterns.

Sun’s Apparent Path

• Changes throughout the year:
  

  • Higher in summer = more daylight and heat.

  • Lower in winter = less daylight and lower temperatures.

Why Are Equatorial Regions Warmest?

• The equator receives direct sunlight all year long.

• Sunlight hits at a 90° angle, which means more energy per area (high insolation).

• Less atmosphere to pass through = less energy lost.

3. Water Cycle & Conservation

Key Processes

1. Evaporation – Water turns into vapor (oceans, lakes).

2. Condensation – Water vapor turns into liquid (clouds).

3. Precipitation – Rain, snow, sleet, or hail falling to Earth.

4. Runoff – Water flows across land into rivers, lakes, oceans.

5. Infiltration – Water soaks into the ground (recharges groundwater).

6. Transpiration – Water vapor released from plants.

Main Energy Source

• The Sun drives the entire water cycle by heating water and causing evaporation.

4. Carbon Cycle & Ecosystems

Forests and Carbon Dioxide

• Forests absorb CO₂ during photosynthesis.

• If forests are destroyed (deforestation), CO₂ remains in the atmosphere, enhancing the greenhouse effect.

Processes that Return Carbon to Atmosphere

• Respiration – by animals and plants.

• Decomposition – of dead organisms.

• Combustion – burning fossil fuels or biomass.

Photosynthesis & Cellular Respiration

• Photosynthesis: CO₂ + water + sunlight → glucose + O₂ (plants).

• Respiration: Glucose + O₂ → CO₂ + water + energy (animals/plants).

• This creates a cycle of carbon and oxygen between organisms and the atmosphere.

5. Milankovitch Cycles & Climate History

Definition

• Long-term changes in Earth’s orbit and orientation that affect climate over tens of thousands of years.

• Responsible for triggering ice ages and warm periods.

Three Types

1. Eccentricity – Shape of Earth’s orbit changes from circular to elliptical (~100,000 years).

2. Obliquity – Changes in the tilt of Earth’s axis (22.1° to 24.5°, every ~41,000 years).

3. Precession – The wobble of Earth’s axis like a spinning top (~26,000 years).

Eccentricity and Climate

• A more elliptical orbit means Earth is sometimes much closer/farther from the Sun.

• This changes the amount of solar energy received and contributes to glacial and interglacial cycles.

6. Paleoclimatology Tools

Tree Rings

• Each year, trees grow a ring.
  

  • Thicker ring = good growing year (warm/wet).

  • Thinner ring = poor growing year (cold/dry).

• Scientists use tree rings to study climate over centuries.

Gas Bubbles in Ice

• Ancient air is trapped in glacial ice.

• Analyzing gas (like CO₂) in bubbles tells us about past atmospheric composition and climate.

Ice Core Layers

• Layers form from seasonal snowfall.

• Light/dark patterns reflect annual cycles.

• Thicker layers = heavy snow years; thin = light snow years.

• Dust and volcanic ash layers tell about past events.

7. Diagrams to Know

Make sure you can label and explain:

1. Earth’s Tilt & Seasons – axial tilt, solstices, equinoxes, Sun angle.

2. Water Cycle – evaporation, condensation, precipitation, etc.

3. Carbon Cycle – arrows showing carbon movement between atmosphere, plants, animals, fossil fuels.

4. Milankovitch Cycles – visuals of eccentricity, obliquity, and precession.