The heat budget of the earth

Long term balance keeps Earths average temperature relatively stable. In exams this is the main summary of heat budget.

Earth's heat budget shows the balance between received solar energy and lost energy. Exam tip: remember it as energy balance.

The Sun is the source of most heat and light energy for Earth. Exam tip: treat solar radiation as the basic energy source.

Energy from the Sun comes as shortwave radiation due to high solar temperature. Exam tip: connect incoming radiation with shortwave.

Earth is relatively cooler so it emits longwave radiation. Exam tip: connect outgoing radiation with longwave.

In the long run received and emitted energy remain nearly equal. Exam tip: understand balance as a long-term average state.

Albedo shows the reflecting ability of a surface. Exam tip: remember that snow and clouds have high albedo.

Snow reflects more solar energy because it is bright. Exam tip: connect bright surfaces with high albedo.

Dark surfaces reflect less and absorb more energy. Exam tip: connect dark surfaces with high absorption.

Insolation is incoming solar radiation received by Earth. Exam tip: treat insolation as incoming solar radiation.

Clouds send a part of solar radiation back to space. Exam tip: connect clouds with reflection.

The basic process is absorption of incoming shortwave solar radiation by the land and ocean surface. When the surface absorbs this energy, its internal energy increases and its temperature rises; it then transfers heat to the atmosphere through conduction, convection and terrestrial radiation. Thus option A, “the surface gets heated,” is the correct general effect. The word “main” does not mean that every place heats equally, because albedo, cloud cover, latitude, season and surface properties modify the amount absorbed. Option B is the opposite of the usual immediate effect. Option C is unrelated to surface absorption, and option D is an exaggerated consequence that does not follow simply from receiving solar energy.

Earth's surface emits energy as longwave radiation after heating. Exam tip: treat terrestrial radiation as surface energy emission.

The atmosphere absorbs and returns part of longwave radiation. Exam tip: understand it as a temperature-control process.

Greenhouse gases absorb part of longwave radiation. Exam tip: treat it as a part of natural heat balance.

Carbon dioxide is a greenhouse gas that absorbs longwave radiation. Exam tip: connect it with the greenhouse effect.

During the day the surface receives direct or indirect solar radiation. Exam tip: connect daytime heating with insolation.

At night solar input stops and the surface emits heat. Exam tip: connect night cooling with terrestrial radiation.

If excess energy is stored Earth will keep warming. Exam tip: connect energy surplus with temperature rise.

Earth’s temperature depends on its energy balance. Incoming solar energy warms the Earth system, while outgoing terrestrial radiation removes energy. If the amount lost becomes greater than the amount received, the planet has a net energy deficit. Over time, this deficit causes the average temperature to fall, so the correct answer is option A. A large temperature increase would require more incoming energy than outgoing energy. The statements about rainfall always stopping or permanent daytime do not follow from the heat budget and are unrelated to the stated condition.

The reasoning can be expressed simply as: energy received minus energy lost equals the change in stored energy. When losses exceed gains, stored energy decreases. Since temperature reflects the thermal energy of the Earth system, decreasing stored energy leads to cooling, at least until a new balance is reached. Short-term or regional variations may differ, but the direct global heat-budget result described in this basic question is a temperature decrease. Therefore, option A follows from the energy deficit.

On the whole Earth the long-term average energy balance remains maintained. Exam tip: connect global balance with long-term average.

Clouds and bright surfaces send part of solar energy back. Exam tip: connect reflection with albedo.

Particles and gases in the atmosphere retain some solar energy. Exam tip: connect absorption with gases and dust.

In scattering light or energy changes direction after striking particles. Exam tip: remember scattering as spreading.

The natural greenhouse effect keeps temperature moderate by trapping some heat. Exam tip: treat the natural greenhouse effect as useful for life.