Climate and Biomes

How is the Earth warmed?

*The balance of incoming and outgoing ultraviolet, visible, and infrared energy (“shortwave radiation”) from the sun drive Earth’s climate

Incoming solar radiation is reflected or absorbed

  • ~1/3 of incoming solar radiation is reflected back (as light + UV) to outer space by gasses in our atmosphere or by Earth’s surface

  • solar radiation that’s not relected is absorbed by gases in our atmosphere or by Earth’s surface, becoming warmer and emitting infrared radiaiton (heat)

  • Earth re-radiates incoming infrared radiation

    • Most re-radiated solar radiation is re-absorbed (as heat) by Earth’s surface

    • some escapes the gasses in our atmosphere and goes into outer space

  • Greenhouse gases absorb infrared radiation

    • GHGs: molecules in Earth’s atmosphere that absorb and re-emit infrared radiation

    • ~99% of gases in the atmosphere are nitrogen (78%) and oxygen (21%) → NOT GHGs

    • naturally-occuring greenhouse effect makes Earth livable → keeps the Earth warm enough to live

    • Natural sources of GHGs:

      • water vapor

      • carbon dioxide

      • methane

    • Human Activity sources of GHGs:

      • halocarbons

      • nitrous oxide

      • carbon dioxide

      • methane

    • Global Warming Potential (GWP): relative measure of how much energy the emissions of 1 ton of a gas will absorb over a given period (100 years)

3 Factors Affect Solar Radiation Received at Different Latitudes:

  • Distance sunlight travels through the atmosphere

    • shorter distance at equator → less solar energy reflected/absorbed by atmosphere

  • Angle at which sunlight hits Earth

    • solar energy is spead over smaller area at equator (more concentrated)

  • Reflectivity of Earth’s surface

    • low albedo (brightness) of dark forests at equator absorb more solar energy than ice at poles

*Albedo: fraction of solar energy reflected by a surface (brightness)


Earth’s Tilt causes seasonal Temperatures

  • Solar Equator: latitude that receives the most direct Sun rays (shifts throughout the year)

  • The northern hemisphere receives more sunlight March → Sept

  • the southern hemisphere receives more sunlight Sept → March


Atmospheric Currents Result from Unequal Heating

  • Atmospheric Currents: circulation patterns of air between Earth’s surface and the atmosphere

  • Physics reminders:

    • warm air rises (thats why we get down when theres a fire)

    • warm air can hold more moisture than cold air (thats why its dry in the winter)

    • air moves from areas of high to low pressure


*Polar cells:

  • ~60degrees N/S, air rises and drops moisture

  • cold, dry air sinks

*Ferrel cells (weak):

  • area between ~30-60degrees N/S, lacking distinct atmospheric currents

  • moves warm air towards the poles and cold air down towards the equator


Different rotation speeds lead to deflected surface air circulation → Coriolis Effect

  • Gyre: large-scale ocean circulation pattern

  • unequal heating: warm water expands, moves away from the equator

  • wind patterns, ocean basin topography and salinity - also affected by coriolis effect

  • Gyres redistribute energy through global oceans


Climate ≠ Weather

Climate: typical atmospheric conditions throughout the year; measured over many years (long term patterns)

Weather: variation in temperature and precipitation in a specific place over periods of hours or days (short term patterns)