2.1.1 The Atmospheric System and Energy Balance Notes

The Earth’s Atmosphere Balances Energy and Sustains Life

1. The Earth’s atmosphere is a mixture of gases, liquids, and solids that regulate energy flow and influence weather systems.
2. It plays a vital role in supporting life and maintaining climate stability.

Weather Happens in the Troposphere

1. The troposphere contains most of the atmosphere’s water vapor, making it the primary layer for weather phenomena, such as clouds, wind, precipitation, and storms.
2. Temperatures decrease by an average of 6.5°C per km with altitude.

The Atmosphere Redistributes Solar Energy

1. The Sun emits energy, whereas the Earth receives it and either reflects it back to space or absorbs it and re-radiates it later.
2. This energy drives global weather systems and climate patterns:
   1. Energy Absorption: Most solar energy is absorbed in tropical regions near the equator.
   2. Energy Redistribution: To maintain balance, wind and ocean currents move energy from warmer tropical regions to cooler polar regions.

The Energy Budget Maintains Climate Balance

1. This balance ensures stable global temperatures and weather patterns.
2. Components of the Energy Budget include:
   1. Incoming Solar Energy (insolation):
      1. 46% absorbed by the Earth’s surface.
      2. 22% drives the hydrological cycle (e.g., evaporation and condensation).
      3. 31% is reflected back into space by clouds, gases, and surfaces.
   2. Outgoing Energy:
      1. Heat is emitted as long-wave radiation, transferred back to the atmosphere.
      2. Processes like conduction (direct contact) and convection (air and liquid movement) facilitate heat transfer.

Insolation is Affected by Latitude, Season, Clouds, and the Composition of the Atmossphere

1. Variation Factors:
   1. Latitude: The Sun’s angle determines how much energy reaches the surface.
   2. Season: Energy varies with the tilt of the Earth’s axis.
   3. Cloud Cover: Thick clouds reduce incoming solar radiation, while clear skies allow more energy to reach the surface.
   4. Composition of the Atmosphere: Natural and human-induced air pollution (suspended particles in the air and gasses) impact the amount of sunlight reaching the surface.

Long-Wave Radiation Balances Earth’s Heat

1. Key Processes:
   1. During the day, incoming solar energy exceeds outgoing long-wave radiation, maintaining energy balance.
   2. At night, cloud cover traps long-wave radiation, reducing heat loss.
   3. Clear skies, however, lead to significant heat loss, especially in deserts.
2. Impact of Clouds:
   1. Cloudy Nights: Less heat escapes, leading to warmer temperatures.
   2. Clear Nights: Greater heat loss results in cooler temperatures and larger temperature swings.

Key Factors Influencing Energy Distribution

1. Surface Albedo: The reflectivity of surfaces impacts how much solar radiation is absorbed or reflected.
   1. High Albedo: Fresh snow reflects 75–90%.
   2. Low Albedo: Dark soil absorbs most energy.
2. Latent Heat Transfer: Heat is stored and released during phase changes (e.g., water evaporation and condensation), powering weather systems like storms.

The Greenhouse Effect is A Natural Process Supporting Life

1. The greenhouse effect is a natural process where greenhouse gases (e.g. water vapor, carbon dioxide, methane, nitrogen oxides) trap heat, keeping the Earth warm enough to sustain life.
2. Without it, the Earth’s average temperature would have been about 33°C cooler, making life impossible.

How the Greenhouse Effect Works

1. Incoming Solar Radiation: Short-wave solar radiation passes through the atmosphere and is absorbed by the Earth’s surface, warming it.
2. Outgoing Long-Wave Radiation: The Earth re-emits heat as long-wave radiation, which is either absorbed or re-radiated back to the surface by greenhouse gases in the atmosphere.
3. Heat Retention: The trapped heat keeps the planet’s average temperature around 15°C, compared to extremes on the Moon (100°C by day, -150°C by night).

The Roles of Various Greenhouse Gases

1. Water Vapor

1. Makes up 95% of greenhouse gases by volume and 50% of the greenhouse effect, but not directly implicated in human-induced climate change.

2. Carbon Dioxide (CO₂)

1. Contributes 20% to the greenhouse effect.
2. Levels increased from 315 ppm (particles per million) (1950) to over 420 ppm (2024), primarily due to:
   1. Burning fossil fuels (coal, oil, natural gas).
   2. Deforestation (removing trees that absorb CO₂).

3. Methane (CH₄)

1. Accounts for 10% of the greenhouse effect, with levels rising by 1% annually.
2. Sources include:
   1. Agriculture (cattle and paddy fields emit large amounts).
   2. Thawing permafrost, which releases trapped methane.

4. Chlorofluorocarbons (CFCs)

1. Synthetic gases that trap up to 10,000 times more heat than CO₂.
2. CFCs damage the ozone layer (different process!) and contribute significantly to global warming.

Global Warming Disrupts the Energy Balance

1. By maintaining the energy balance, the Earth has enjoyed a stable climate during Holocene - last ~12 thousand years.
2. Global warming occurs when greenhouse gases, like CO₂ and methane, trap additional heat in the atmosphere, disrupting the energy balance.
3. Its impacts include:
   1. Rising temperatures that alter global wind and ocean currents.
   2. Increasing evaporation that accelerates water cycle intensifying weather events.
   3. Melting ice caps that reduce reflection, amplifying warming (positive feedback loop) and cause rising sea levels.