Earth's energy budget refers to the tracking of how much energy is flowing into and out of the Earth's climate, where the energy is going, and if the energy coming in balances with the energy going out. The Earth receives energy from the Sun, and it also reflects and radiates energy back into space. All of the energy that warms the atmosphere, oceans and land must be radiated back into space in order to maintain our current climate. If the amount of energy radiating back into space is decreased by even a very small amount, it can lead to warming. It is believed that increasing levels of carbon dioxide in the atmosphere has a 'greenhouse effect' of reducing the amount of energy radiated into space.
1. ENERGY BUDGET OF EARTH
Presented by:
Hemant
M.Sc. Environment studies
17001556002
CEEES (DEENBANDHU CHOTU RAM UNIVERSITY OF SCIENCE AND
TECHNOLOGY, MURTHAL, SONIPAT)
3. INTRODUCTION
Earth's energy budget refers to the tracking of how much energy is flowing into and
out of the Earth's climate, where the energy is going, and if the energy coming in
balances with the energy going out. The Earth receives energy from the Sun, and it
also reflects and radiates energy back into space. This balance of incoming and
outgoing energy creates our climate that supports life as we know it on Earth. The Law
of Conservation of Energy states that energy can neither be created nor destroyed, but
it can be transformed from one state to another. Energy from the Sun is delivered as
light energy, and some of that energy is used to warm the Earth, and the differences in
densities of air and water between warm and cold regions of the atmosphere and
oceans induce currents. Heat also drives the evaporation of water from the oceans
and drives the water cycle. Some light energy is converted into chemical energy
through photosynthesis, and stored as biomass.
All of the energy that warms the atmosphere, oceans and land must be radiated back
into space in order to maintain our current climate. If the amount of energy radiating
back into space is decreased by even a very small amount, it can lead to warming. It is
believed that increasing levels of carbon dioxide in the atmosphere has a 'greenhouse
effect' of reducing the amount of energy radiated into space.
4. INCOMING SOLAR RADIATION
The sun radiates mostly in the visible band, but also in the ultraviolet (shorter wavelength).
When averaged globally and annually, only 51% of the solar radiation striking the earth and
its atmosphere is absorbed at the surface.
The atmosphere absorbs 19% of incoming solar radiation and the remaining 30% is
reflected back into space.
The shortest wavelengths of solar radiation (those most dangerous to life) are absorbed by
molecules in the upper and middle atmosphere.
In particular, ozone selectively absorbs ultraviolet radiation while allowing visible radiation
to pass through relatively unhindered.
Reflection significantly affects the solar radiation that reaches the ground, as the sun's rays
could be reflected off of air molecules (termed scattering), clouds or the ground itself.
Light-colored or shiny objects reflect more radiation than dark objects. Energy that is
reflected cannot be absorbed or transmitted through an object.
Meteorologists refer to the percent of radiation returning from a surface compared to the
incident radiation as the "albedo". For example, the earth reflects an average of 30% of the
incoming radiation, so the average albedo is 30%, or 0.3. Most of the earth's average
reflection results from clouds.
7. OUTGOING TERRESTRIAL RADIATION
The earth's surface, atmosphere, and clouds emit radiation in the infrared band
and near-infrared band.
Outgoing infrared (IR) radiation from the earth's surface (also called terrestrial
radiation) is selectively absorbed by certain molecules, particularly water vapor
and carbon dioxide.
Gases which absorb IR radiation are termed collectively as "greenhouse gases".
Water vapor and carbon dioxide emit infrared radiation.
Infrared radiation from greenhouse gases in the atmosphere is emitted in all
directions, including back to the earth's surface. It is this re-emission to the earth's
surface that maintains a higher temperature on our planet than what would be
possible without the atmosphere.
Condensed water is also an efficient absorber and emitter of IR radiation. Thus,
clouds act in a manner similar to greenhouse gases.