Earth's Temperature & Radiation Balance

What determines Earth's temperature?

The balance between incoming radiation absorbed and outgoing radiation emitted, together with reflection into space.

What is the main source of energy reaching Earth?

Electromagnetic radiation from the Sun.

What happens to some incoming solar radiation?

It is reflected back into space by clouds, the atmosphere and Earth's surface.

What happens to solar radiation absorbed by Earth's surface?

It transfers energy to the surface, increasing its thermal energy.

How does Earth transfer energy back towards space?

Mainly by emitting infrared radiation.

What happens if Earth absorbs more radiation than it emits?

Earth's average temperature tends to increase.

What happens if Earth emits more radiation than it absorbs?

Earth's average temperature tends to decrease.

What happens when absorbed and emitted radiation are balanced?

Earth's average temperature remains approximately constant, assuming other energy transfers are balanced.

Why do different surfaces absorb different amounts of solar radiation?

They have different reflectivities and absorptivities.

Why can dark surfaces warm more quickly in sunlight?

They generally absorb more incident radiation than light-coloured surfaces.

Why can snow and ice help keep Earth's surface cooler?

They reflect a large proportion of incoming solar radiation.

What is albedo?

The proportion of incoming radiation reflected by a surface.

What happens when Earth's average albedo increases?

More solar radiation is reflected into space, tending to reduce warming.

What happens when Earth's average albedo decreases?

More solar radiation is absorbed, tending to increase warming.

What is the greenhouse effect?

The warming effect caused when greenhouse gases absorb and emit infrared radiation, reducing the rate at which energy escapes to space.

How do greenhouse gases affect outgoing infrared radiation?

They absorb and re-emit some infrared radiation, including towards Earth's surface.

Why can an increase in greenhouse gases raise Earth's average temperature?

It can reduce outgoing energy transfer to space at a given surface temperature, causing warming until a new balance is reached.

Why do clouds affect Earth's temperature?

They can reflect incoming sunlight and absorb and emit infrared radiation.

Why is Earth's radiation balance important?

It determines whether Earth experiences net warming, net cooling or approximately stable temperatures.

How can a radiation-balance diagram be interpreted?

Compare the incoming, reflected, absorbed and emitted energy flows to determine whether there is a net gain or loss.