Heat Budget or Heat Balance
Atmospheric Phenomenas:-
- Insolation: The sun's short-wave radiation that reaches the Earth
- Terrestrial radiation: The long-wave radiation that the Earth emits back into space
- Reflection: The Earth's atmosphere, clouds, and surface reflect some of the sun's radiation back into space
- Absorption: The Earth's atmosphere, clouds, and surface absorb some of the sun's radiation
- Evaporation, convection, rainfall, winds, and ocean circulation: These processes help to balance out the uneven heating from the sun
Heat Budget Components
If the Earth's
heat budget were not balanced, the Earth would either get too hot or too
cold. The sun's uneven heating of the Earth is the root cause of all
climatic characteristics.
(a) Insolation
– Insolation refers to the incoming shortwave solar
radiation to the earth’s surface. The processes involved with insolation in
maintaining heat balance include:
(b) Reflection – Reflection occurs when incoming solar waves bounce back from a surface
that it strikes in the atmosphere, on land, or water, and are not transformed
into heat.
(c) Absorption – Absorption of radiation involves the conversion of electromagnetic
radiation into heat energy.
(d) Scattering – Scattering of solar waves takes place when the radiation strikes small
objects in Earth’s atmosphere, such as air molecules or water droplets or
aerosols which disperse the solar waves in all directions.
(e) Terrestrial
Radiation – Terrestrial Radiation refers to longwave radiation
that is emitted by the Earth׳s surface or by the atmosphere. The processes
involved with Terrestrial Radiation in maintaining heat balance include
(f) Latent heat
transfer – It is the amount of heat transferred during the
point where one substance is ready to change its state.
Example: From
solid to liquid or from liquid to gas,
(g) Sensible
heat transfer – It is the energy that is transferred as heat to an
object, without any change in the state
(h) Emission by
vapour and clouds – Huge amounts of terrestrial
radiation are also released by the water vapour and clouds.
How is the Heat Budget of Earth Analyzed and Calculated?
Consider that
100 percent insolation is received at the top of the atmosphere. While passing
through the atmosphere, some energy is reflected, scattered, and absorbed,
leaving only a fraction to reach Earth's surface.Around 35 units are reflected
into space even before reaching the Earth's surface. Among these, 27 units are
reflected from cloud tops and 2 units from snow and ice-covered areas,
collectively known as the Earth's albedo.
The Earth emits 51 units as terrestrial radiation. Of this, 17 units are emitted directly into space, and the remaining 34 units are absorbed by the atmosphere. Among these, 6 units are directly absorbed, 9 units through convection and turbulence, and 19 units through the latent heat of condensation. The remaining 65 units are absorbed by the Earth and its atmosphere. Out of this, 14 units are absorbed within the atmosphere, and 51 units are absorbed by the Earth's surface.
The atmosphere emits back 48 units (14 units from insolation and 34 units from terrestrial radiation) into space.Hence, the total radiation returning from Earth and the atmosphere is 17 and 48 units, respectively, summing up to 65 units, thus balancing the 65 units of solar insolation received.
Causes of Variation in the Heat Budget of Earth
- Even though the Earth retains a balance between
insolation and terrestrial radiation, we do not find this at all
latitudes.
- The insolation and heat budget in the tropical
zone is larger than that of terrestrial radiation. As a result, it is a
location that has excess heat.
- The heat gain in the polar zone is lesser than
the heat loss. As a result, it is a region with a heat deficit.
- Therefore, insolation and heat budget cause an
imbalance of heat at different latitudes.
- Winds and ocean currents, which carry heat from
zones of surplus heat to heat deficit zones, aid in the mitigation of this
imbalance to some extent.
- This process of redistribution and balancing of
latitudinal heat is termed latitudinal heat balance.
Effects of the Heat Budget of Earth on the Climate System of Earth
- The heat budget of the Earth is significant in
establishing the Earth’s climate. When the heat budget balances, the
temperature on the Earth remains comparatively constant, with no overall
increase or decrease in average temperature.
- Global weather and climate variations are caused
by the uneven heating of the Earth and its atmosphere. This uneven heating
occurs due to latitudinal and seasonal variations in insolation.
- The energy that comes to the Earth and the energy
that is emitted from the Earth does not balance. This imbalance is partly
caused by the energy received from the sun, which changes with the seasons
and changes in the composition of the Earth’s atmosphere. Variations in
the composition of Earth’s atmosphere alter the amount of energy absorbed
and reflected by the atmosphere. Changing factors such as these result in
a very low but substantial energy imbalance on the Earth.
- As human activities increase the quantity of
carbon dioxide in the atmosphere, the energy imbalance builds up. The
Earth’s temperature will rise in response to account for this imbalance.
Since the amounts of carbon dioxide and other greenhouse gasses in our
atmosphere are rising, this value is anticipated to increase yearly,
contributing even more to rising temperatures.
- Earth Radiation balance: It is this imbalance in
the heat budget of the Earth that results in rising temperatures on the
Earth, one of the most substantial effects of climate change.
Importance of Heat Budget of Earth
- The heat balance of the Earth is a crucial
component of what makes it livable, and the heat budget of the Earth
attains this.
- It keeps the planet warm.
- It is essential for enhancing the manufacturing
of solar panels that capture and convert this energy.
- It is accountable for the change in temperature
from the equator to the poles.
- It aids in the process of photosynthesis and
hence the growth of plants.
- It is also responsible for the variation in the
rain patterns from the equator to the poles.
Conclusion
The sun is the ultimate source of heat. The differential heat obtained from the sun is distributed differently across the globe, which is the ultimate reason behind all climatic traits. Hence, understanding the Heat Budget of the Earth and the distribution of temperature in different seasons is crucial for understanding other climatic features such as wind systems, pressure systems, precipitation and so on.
