The balance between the incoming solar radiation received by the Earth and the outgoing radiation lost to space is called the:

The Earth's heat budget (or energy budget) is the balance between the energy the Earth receives from the Sun and the energy it sends back to space. Because the two are roughly equal over time, the Earth's average temperature stays fairly constant.

Incoming solar radiation (insolation):

Consider 100 units of solar energy reaching the top of the atmosphere.

About 35 units are reflected back to space without heating the Earth: about 27 units from clouds, 2 units from snow and ice, and the rest by scattering in the atmosphere. This reflected fraction is called the Earth's albedo.

About 14 units are absorbed by the atmosphere.

About 51 units are absorbed by the Earth's surface.

Outgoing radiation:

• The Earth's surface, having absorbed 51 units, gives this energy back as long-wave (infrared) terrestrial radiation.
• Much of it is absorbed by greenhouse gases and later radiated back to space by the atmosphere.
• In total, 65 units (14 from the atmosphere's own absorption plus 51 from the surface) are eventually lost to space, balancing the 65 units absorbed.

Latitudinal imbalance:

• Between about 40 degrees North and 40 degrees South, the Earth receives more energy than it loses (a surplus).
• Near the poles, it loses more than it receives (a deficit).
• This imbalance is corrected by the transfer of heat from the tropics towards the poles through winds and ocean currents.

Why the heat budget matters:

The increase in greenhouse gases due to human activities traps more outgoing radiation, upsetting the balance and causing global warming.

Why not the other options?

• ✗Albedo is the fraction of sunlight reflected by a surface or by the Earth as a whole (about 0.3).
• ✗The greenhouse effect is the trapping of outgoing infrared radiation by certain gases.
• ✗Lapse rate is the rate at which temperature falls with height in the troposphere, about 6.5 degrees Celsius per kilometre.