The climate system

Our planet’s climate is a complex system powered by solar radiation.  “There are three fundamental ways to change the radiation balance of the Earth:

1) by changing the incoming solar radiation (e.g., by changes in Earth’s orbit or in the Sun itself);

2) by changing the fraction of solar radiation that is reflected (called ‘albedo’; e.g., by changes in cloud cover, atmospheric particles or vegetation); and

3) by altering the longwave radiation from Earth back towards space (e.g., by changing greenhouse gas concentrations).”

Components of the climate system:

At the planet level our climate system comprises five key components and the interactions between them:

  • The atmosphere (the gases that surround the planet);
  • The hydrosphere (dominated by the oceans but also including fresh water, rivers, lakes, and groundwater);
  • The biosphere (all living things and soils);
  • The cryosphere (ice sheets; sea ice and mountain glaciers);
  • The lithosphere (the surface of the earth’s crust).

These five elements are linked by a series of dynamic cycles, such as the water cycle, which together generate our climate and weather.  Affecting these cycles are a number of feedback mechanisms (both positive – accumulative; and negative – dampening) and external forcings.

It has been suggested by another student on the course that we could separate out humanity as a sixth key component in the system, as the ‘anthroposphere’, as we enter into the anthropocene (with thanks to Paul Price).

Feedback mechanisms: positive (amplifying) and negative (diminishing)

Within the climate system are a series of feedback mechanisms, which directly affect the planet’s climate.  They three key ones are:

  • Water vapour feedback (positive feedback – increased planetary temperature causes more water vapour to evaporate from the hydrosphere and travel to the atmosphere, where it acts as a blanket gas, causing the planet’s temperature to again increase).
  • Ice albedo feedback (positive feedback – increased temperature causes more ice to melt, which reduces the area of heat reflective ice and increases the area of heat absorbing dark sea, in turn increasing planetary temperature)
  • Radiation feedback (negative feedback – when a planetary element such as the lithosphere is warm, it radiates heat, causing it to lose energy, causing it to cool down.)

External forcings:

External forcings are factors that are external to the climate system that have the capacity to alter it.  They include:

  • Volcanic eruptions ejecting aerosols high into the atmosphere;
  • Solar variations sending increased or diminished quantities of solar radiation to the earth’s surface;
  • Human-made gases, namely carbon dioxide, methane, nitrous oxide, ozone and CFCs entering the atmosphere

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