Radiation, Global Energy Budget, and Temperature

Energy from the Sun drives Earth's climate system.
- This energy travels through space as electromagnetic radiation (EMR).

All EMR travels at the speed of light, approximately 186,000 miles per second.
All objects with temperatures greater than 0^ ext{o} Kelvin (-273^ ext{o} C) radiate EMR.
Warmer objects emit a greater amount of EMR than cooler objects.
Warmer objects emit EMR at shorter wavelengths.

The Sun is extremely hot, with a surface temperature of approximately 5500^ ext{o} C (9,900^ ext{o} F).
EMR is emitted from the Sun in all directions.
The Sun mainly emits ultraviolet, visible light, and short-wave infrared radiation.
This is collectively referred to as shortwave radiation or incoming solar radiation.

Wavelength is defined as the distance between wave crests. The unit nanometer (nm) is (10^{-9}m), micrometer (\mu m) is (10^{-6}m) and millimeter (mm) is (10^{-3}m).
Electromagnetic Spectrum:
- Shorter Wavelengths (Higher Energy):
  - Gamma rays: .001nm (10^{-12}m) - Penetrate Earth's atmosphere.
  - X-rays: 1nm (10^{-9}m).
  - Ultraviolet: 10^{-8}m - Partially penetrates Earth's atmosphere.
  - Visible light: .5 \times 10^{-6}m - Fully penetrates Earth's atmosphere, crucial energy in Earth's climate system.
  - Infrared: 10^{-5}m - Partially penetrates Earth's atmosphere.
- Longer Wavelengths (Lower Energy):
  - Microwaves: 1mm (10^{-3}m) to 10^{-2}m - Partially penetrates Earth's atmosphere.
  - Radio waves: 1m to 10^3m - Fully penetrates Earth's atmosphere.
Temperature of emitting bodies (K) for different wavelengths:
- 10^{-12}m (Gamma Ray): 10 Million K (e.g., atomic nuclei).
- 10^{-10}m (X-ray):
- 10^{-8}m (Ultraviolet): 10,000 K.
- 10^{-5}m (Infrared): 100 K.
- 1m (Radio): 1 K.
Sun's EMR Emission Intensity: Peaks in the visible light range (around .5 micrometers), with significant output in ultraviolet and short-wave infrared.

Earth's average temperature is much cooler, around 15^ ext{o} C (59^ ext{o} F).
Earth mainly emits thermal infrared EMR.
This is referred to as long-wave radiation.
Earth's EMR Emission Intensity: Peaks in the long-wave infrared range (around 10 micrometers).

Transmission: Radiation passes through a medium (e.g., atmosphere, ocean, soil) without significant loss or change in intensity.
Absorption: The energy of radiation is converted into heat by the medium.
Scattering: Weaker radiation is diffused or dispersed in multiple directions.
Reflection: Radiation bounces off a surface without losing intensity.

Albedo is a measure of a surface's reflectivity, expressed as the percentage of incoming solar radiation reflected from that surface.
High Albedo (40-90%): Surfaces like fresh snow (e.g., Denali, AK) reflect a large portion of energy.
Intermediate Albedo (25-60%): Examples include some agricultural lands or partially cloudy skies.
Low Albedo (5-20%): Surfaces like dark soil, asphalt, or open ocean absorb most of the energy.
Examples: Clouds can have intermediate albedo (10-60%), while open water tends to have low albedo (10-20%).

Radiation:
- Requires no transfer medium.
- Energy is transmitted by electromagnetic waves.
- This is the primary mechanism of energy transmission from the Sun to Earth.
Conduction:
- Transfer of energy through direct molecular contact, from higher to lower energy areas.
- Air is a poor conductor of energy.
- It is particularly important for heat transfers occurring very close to a surface (e.g., between the ground and the lowest layer of air).
  - Example: Heat transfer in tundra soil between thawed and frozen layers.
Convection:
- Transfer of energy by the movement of a fluid (liquid or gas).
- Less dense (warmer) fluid rises, displacing denser (cooler) fluid.
- Includes: Sensible Heat Transfer and Latent Heat Transfer.
- a) Sensible Heat Transfer:
  - Occurs when air or water of one temperature moves to a location with a different temperature, directly transferring heat.
- b) Latent Heat Transfer:
  - Heat transfer associated with the movement of water vapor.
  - Critical processes include evaporation and evapotranspiration, where heat is absorbed during phase change and released elsewhere.