Earth’s heat budget

Earth's heat budget: balance of incoming and outgoing heat on earth is referred to as its heat budget. The heat budget appears below

of all the solar radiation reaching the earth, 30% is reflected back to space from clouds, water, and the surface. the remaining 70% is absorbed by the earth(47% by the land & ocean and 23% by the atmosphere). the heat absorbed by the land & ocean is exchanged by the atmosphere in the form of conduction, radiation, and latent heat( phase change). 

Conduction: transfer for energy(heat energy) between particles when they are in contact with each other. air is a poor conductor, so the transfer of energy from conduction between the earth and the atmosphere is very less (about 7% of the incoming solar radiation)

Energy from the sun is emitted in short wave radiation due to high temperature, it takes 8 min for this energy to reach the surface of the earth, we experience this as a combination of visible light and radiant heat. Energy from the earth is emitted as longwave radiation as the earth is much colder than the sun all the longwave radiation emitted by earth would pass directly to space. almost all the gases that make the atmosphere of the earth are transparent except ozone, which observes the UV portion of the incoming solar radiation from the sun. 

The atmosphere contains many gases which include greenhouse gases like Hydrogen, carbon dioxide, and methane. these gases are transparent to incoming short wave radiation but opaque to some wavelengths of longwave radiation from the earth. molecules of these gases absorb long waveform the earth and remit less longwave radiation than they absorb, which traps some of the heat energy in the atmosphere and cause earth temperature to increase(greenhouse effect)

Many scientists believe that the venus has experienced what's called a "runaway greenhouse effect" causing it to become the hottest planet in the solar system with a temperature of  462ºC. early in the history  of our sun venus may have had a global ocean, as the sun got stronger, the global ocean got began to evaporate. as the water vapour is a green house gas hence the amount of long wave radiation trapped in atmosphere of venus increased. causing the temperature to rise. the hotter temperature eventually led to the ocean boiling away creating more water vapours, over time Hydrogen escaped from the atmosphereleaving the oxygen to combine with carbon now venus has an atmosphere with 96.5% of Carbon Dioxide. 

Greenhouse effect is also responsible for climate change or global warming. since the industrial revolution the percentage of  green house gases especially Carbon Dioxide, and Methane has increased drastically, which results in the rapid warming of the global climate. Carbon Dioxide concentration in the atmosphere has increased about 25% due to which the global temperature has risen 0.5ºC over the century. Unless the production of these green houses is restricted, this rapid warming trend may continue, with potential dire consequences. 

The largest pathway for heat exchange between the land. ocean and the atmosphere is through the laterng heat (phase change). when water chages it's phase either the heat is absorbed or the heat is released, and these phase changes transfer hear between the ocean and the atmosphere. the heat that is absorbed by the atmosphere either directly from solar radiation or as a result of conduction, radiation and latent heat, is eventually radiated back into space

Inbalance in heating of earth's surface

we all know that earth is an elliptical body. hence the sunlight distrubated over its surface is not equal. different region od the earth receive differnt amount of sunlight. this difference occur because of different reasons. 

the sunlight falls perpendicular to the surface of the earth only at equatorial region, and in the rest of the regions the angle between the incoming solar radiation and the surface of the earth is less than 90º . the same amount of income radiation falls on a small area ar equator but it will be spread over a large area ar poles. Thus the tropics receive more intense sunlight and a greater amount of heating per unit of area than the polar regions. at poles higher amount of energy is reflected back into the space, poles have higher albedo. and at equator the energy is absorbed which is why Equator region is warm compared to the poles. 

the interest fact to be notic here is that the poles emit more heat energy than the receive and the tropic region emits less energy than they receive. so we can expect that in coming time the poles may become more cool than present and the equator region may become more warmer than present., yet this is not the case so what is happening? 

it's a simple mechanism. the heat absorbed at the equator region is not isolated, some of the absorbed energy (about 20%) is moved at the poles, this 20% of energy and the actual heat absorbed at poles is emitted from the poles back to the space. which actually increases the amount of emitted energy at poles and decreases at the tropics. this mechanism is known as ocean and atmospheric circulation.