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 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