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# 1.2 Forcing the global thermostat

Forcings either alter the energy into the planet, or the energy out, pushing the climate into a warmer or cooler state (unless an equal forcing is acting in the opposite way). Depending on the size and type of forcing, it may take thousands of years for the climate to finish responding.

Figure 1 illustrates an analogy for a radiative forcing: it is simply something that acts to change the Earth’s energy budget (which results in a climate change). In this case the ‘suspect’ radiative forcing is a mystery hand.

Figure 1 A ‘radiative forcing’ (mystery hand) acts to change the ‘Earth’s energy budget’ (thermostat dial) which produces a change in climate (room temperature).

Forcings are measured in watts per metre squared (W/m2). One watt (1 W) is defined as 1 joule per second. This is a unit that is commonly used in electric lightbulbs, with modern bulbs using ~15 W/m2.

You will now take a closer look at the various ‘suspects’ and ‘red herrings’ that have acted to change this budget in the past and therefore warmed or cooled the planet.

◄Contents►Next: 2 Radiative forcings – increasing temperature

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