Earth radiation balance

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Energy budget of the Earth.

Earth’s radiation balance

The assortment of different heat (energy) fluxes involved in the Earth’s radiation balance is shown in the diagram to the right. There are several different key fluxes, including the heating of the Earth by the Sun and the escape of Earth’s heat to space. Hot objects tend to lose heat to their surroundings. Even though space is a vacuum and hence unable to transport heat by conduction, even so the Earth loses heat to space by different means. Earth heat loss is predominantly by way of emission of infra-red radiation. Some of the Sun’s incoming heat is also directly reflected back to space due to the Earth's brightness. And then there is also the greenhouse effect, the ‘insulating blanket’ that blocks some of the infra-red heat loss to space.

These and other aspects make up the interesting system that is Earth’s energy balance. If any one component of this system is altered then the system automatically re-adjusts to re-balance incoming and outgoing radiation. The timescale of adjustment is influenced by the thermal inertia of the Earth, which is principally made up of the thermal inertia of the ocean. The large amount of energy input required to heat up each cubic metre of seawater introduces (on the global scale) a time lag between any change in radiative heating and the resulting (eventual) change in Earth temperature. This is an important aspect of global warming.

The following phenomena can be explored using the Jmodels energy balance model:

(a) global warming: including the greenhouse effect and the time lag in heating.

(b) global dimming: the effect of anthropogenic aerosols in blocking incoming sunlight and thereby masking some of the global warming.

(c) energy balance on other planets: and the Goldilocks problem.

(d) Faint Young Sun: the Sun was much fainter during Earth’s early history, so how come the early Earth didn't freeze over?

(e) volcanic eruptions: why did the eruption of Mount Pinatubo have such a large effect on climate? What should we expect from larger eruptions?

Further Reading

  • Henderson-Sellers, A. and McGuffie, K. (1997). A Climate Modelling Primer, 2nd Edition, John Wiley and Sons Ltd.