Earth's energy budget accounts for the balance between the energy Earth receives from the Sun,and the energy the Earth radiates back into outer space after having been distributed throughout the five components of Earth's climate system and having thus powered Earth’s so-called heat engine. This system is made up of Earth's water, ice, atmosphere, rocky crust, and all living things.
In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of 1 metre against a force of 1 newton.
Outer space, or simply space, is the expanse that exists beyond the Earth and between celestial bodies. Outer space is not completely empty—it is a hard vacuum containing a low density of particles, predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays. The baseline temperature of outer space, as set by the background radiation from the Big Bang, is 2.7 kelvins. The plasma between galaxies accounts for about half of the baryonic (ordinary) matter in the universe; it has a number density of less than one hydrogen atom per cubic metre and a temperature of millions of kelvins; local concentrations of this plasma have condensed into stars and galaxies. Studies indicate that 90% of the mass in most galaxies is in an unknown form, called dark matter, which interacts with other matter through gravitational but not electromagnetic forces. Observations suggest that the majority of the mass-energy in the observable universe is dark energy, a type of vacuum energy that is poorly understood. Intergalactic space takes up most of the volume of the universe, but even galaxies and star systems consist almost entirely of empty space.
Earth's climate arises from the interaction of five major climate system components: the atmosphere (air), the hydrosphere (water), the cryosphere, the lithosphere and the biosphere. Energy, water and different chemical elements are constantly flowing between the different components of the system. Climate is the average of weather, typically over a period of 30 years, and is determined by a combination of processes in the climate system.
Quantifying changes in these amounts is required to accurately model the Earth's climate.
Received radiation is unevenly distributed over the planet, because the Sun heats equatorial regions more than polar regions. "The atmosphere and ocean work non-stop to even out solar heating imbalances through evaporation of surface water, convection, rainfall, winds, and ocean circulation."Earth is very close to being in radiative equilibrium, the situation where the incoming solar energy is balanced by an equal flow of heat to space; under that condition, global temperatures will be relatively stable. Globally, over the course of the year, the Earth system—land surfaces, oceans, and atmosphere—absorbs and then radiates back to space an average of about 340 watts of solar power per square meter. Anything that increases or decreases the amount of incoming or outgoing energy will change global temperatures in response.
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. The surrounding gas must not be saturated with the evaporating substance. When the molecules of the liquid collide, they transfer energy to each other based on how they collide with each other. When a molecule near the surface absorbs enough energy to overcome the vapor pressure, it will escape and enter the surrounding air as a gas. When evaporation occurs, the energy removed from the vaporized liquid will reduce the temperature of the liquid, resulting in evaporative cooling.
Radiative equilibrium is one of the several requirements for thermodynamic equilibrium, but it can occur in the absence of thermodynamic equilibrium. There are various types of radiative equilibrium, which is itself a kind of dynamic equilibrium.
However, Earth's energy balance and heat fluxes depend on many factors, such as atmospheric composition (mainly aerosols and greenhouse gases), the albedo (reflectivity) of surface properties, cloud cover and vegetation and land use patterns.
Albedo is the measure of the diffuse reflection of solar radiation out of the total solar radiation received by an astronomical body. It is dimensionless and measured on a scale from 0 to 1.
Changes in surface temperature due to Earth's energy budget do not occur instantaneously, due to the inertia of the oceans and the cryosphere. The net heat flux is buffered primarily by becoming part of the ocean's heat content, until a new equilibrium state is established between radiative forcings and the climate response.
Inertia is the resistance of any physical object to any change in its velocity. This includes changes to the object's speed, or direction of motion. An aspect of this property is the tendency of objects to keep moving in a straight line at a constant speed, when no forces act upon them.
An ocean is a body of water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans. The word "ocean" is often used interchangeably with "sea" in American English. Strictly speaking, a sea is a body of water partly or fully enclosed by land, though "the sea" refers also to the oceans.
The cryosphere is an all-encompassing term for those portions of Earth's surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps, ice sheets, and frozen ground. Thus, there is a wide overlap with the hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation. Through these feedback processes, the cryosphere plays a significant role in the global climate and in climate model response to global changes. The term deglaciation describes the retreat of cryospheric features. Cryology is the study of cryospheres.
In spite of the enormous transfers of energy into and from the Earth, it maintains a relatively constant temperature because, as a whole, there is little net gain or loss: Earth emits via atmospheric and terrestrial radiation (shifted to longer electromagnetic wavelengths) to space about the same amount of energy as it receives via insolation (all forms of electromagnetic radiation).
To quantify Earth's heat budget or heat balance, let the insolation received at the top of the atmosphere be 100 units (100 units = about 1,360 watts per square meter facing the sun), as shown in the accompanying illustration. Called the albedo of Earth, around 35 units are reflected back to space: 27 from the top of clouds, 2 from snow and ice-covered areas, and 6 by other parts of the atmosphere. The 65 remaining units are absorbed: 14 within the atmosphere and 51 by the Earth’s surface. These 51 units are radiated to space in the form of terrestrial radiation: 17 directly radiated to space and 34 absorbed by the atmosphere (19 through latent heat of condensation, 9 via convection and turbulence, and 6 directly absorbed). The 48 units absorbed by the atmosphere (34 units from terrestrial radiation and 14 from insolation) are finally radiated back to space. These 65 units (17 from the ground and 48 from the atmosphere) balance the 65 units absorbed from the sun in order to maintain zero net gain of energy by the Earth.
The total amount of energy received per second at the top of Earth's atmosphere (TOA) is measured in watts and is given by the solar constant times the cross-sectional area of the Earth corresponded to the radiation . Because the surface area of a sphere is four times the cross-sectional surface area of a sphere (i.e. the area of a circle), the average TOA flux is one quarter of the solar constant and so is approximately 340 W/m². Since the absorption varies with location as well as with diurnal, seasonal and annual variations, the numbers quoted are long-term averages, typically averaged from multiple satellite measurements.
Of the ~340 W/m² of solar radiation received by the Earth, an average of ~77 W/m² is reflected back to space by clouds and the atmosphere and ~23 W/m² is reflected by the surface albedo, leaving ~240 W/m² of solar energy input to the Earth's energy budget. This gives the earth a mean net albedo of 0.29.
The geothermal heat flux from the Earth's interior is estimated to be 47 terawatts watt/square metre, which represents only 0.027% of Earth's total energy budget at the surface, which is dominated by 173,000 terawatts of incoming solar radiation.and split approximately equally between radiogenic heat and heat leftover from the Earth's formation. This comes to 0.087
Human production of energy is even lower, at an estimated 18 TW.[ citation needed ]
Photosynthesis has a larger effect: photosynthetic efficiency turns up to 2% of the sunlight striking plants into biomass. 100 to 140 [ clarification needed ]TW (or around 0.08%) of the initial energy gets captured by photosynthesis, giving energy to plants.
Other minor sources of energy are usually ignored in these calculations, including accretion of interplanetary dust and solar wind, light from stars other than the Sun and the thermal radiation from space. Earlier, Joseph Fourier had claimed that deep space radiation was significant in a paper often cited as the first on the greenhouse effect.
Longwave radiation is usually defined as outgoing infrared energy leaving the planet. However, the atmosphere absorbs parts initially, or cloud cover can reflect radiation. Generally, heat energy is transported between the planet's surface layers (land and ocean) to the atmosphere, transported via evapotranspiration and latent heat fluxes or conduction/convection processes.Ultimately, energy is radiated in the form of longwave infrared radiation back into space.
Recent satellite observations indicate additional precipitation, which is sustained by increased energy leaving the surface through evaporation (the latent heat flux), offsetting increases in longwave flux to the surface.
If the incoming energy flux is not equal to the outgoing energy flux, net heat is added to or lost by the planet (if the incoming flux is larger or smaller than the outgoing respectively).
An imbalance must show in something on Earth warming or cooling (depending on the direction of the imbalance), and the ocean being the largest thermal reservoir on Earth, is a prime candidate for measurements.
Earth's energy imbalance measurements provided by Argo floats have detected an accumulation of ocean heat content (OHC). The estimated imbalance was measured during a deep solar minimum of 2005–2010 to be 0.58 ± 0.15 W/m². This level of detail cannot be inferred directly from measurements of surface energy fluxes, which have combined uncertainties of the order of ± 17 W/m².
Several satellites indirectly measure the energy absorbed and radiated by Earth and by inference the energy imbalance. The NASA Earth Radiation Budget Experiment (ERBE) project involves three such satellites: the Earth Radiation Budget Satellite (ERBS), launched October 1984; NOAA-9, launched December 1984; and NOAA-10, launched September 1986.
Today NASA's satellite instruments, provided by CERES, part of the NASA's Earth Observing System (EOS), are designed to measure both solar-reflected and Earth-emitted radiation.
The major atmospheric gases (oxygen and nitrogen) are transparent to incoming sunlight but are also transparent to outgoing thermal (infrared) radiation. However, water vapor, carbon dioxide, methane and other trace gases are opaque to many wavelengths of thermal radiation. The Earth's surface radiates the net equivalent of 17 percent of the incoming solar energy in the form of thermal infrared. However, the amount that directly escapes to space is only about 12 percent of incoming solar energy. The remaining fraction, 5 to 6 percent, is absorbed by the atmosphere by greenhouse gas molecules.
When greenhouse gas molecules absorb thermal infrared energy, their temperature rises. Those gases then radiate an increased amount of thermal infrared energy in all directions. Heat radiated upward continues to encounter greenhouse gas molecules; those molecules also absorb the heat, and their temperature rises and the amount of heat they radiate increases. The atmosphere thins with altitude, and at roughly 5–6 kilometres, the concentration of greenhouse gases in the overlying atmosphere is so thin that heat can escape to space.
Because greenhouse gas molecules radiate infrared energy in all directions, some of it spreads downward and ultimately returns to the Earth's surface, where it is absorbed. The Earth's surface temperature is thus higher than it would be if it were heated only by direct solar heating. This supplemental heating is the natural greenhouse effect.It is as if the Earth is covered by a blanket that allows high frequency radiation (sunlight) to enter, but slows the rate at which the low frequency infrared radiant energy emitted by the Earth leaves.
A change in the incident radiated portion of the energy budget is referred to as a radiative forcing.
Climate sensitivity is the steady state change in the equilibrium temperature as a result of changes in the energy budget.
Climate forcings are changes that cause temperatures to rise or fall, disrupting the energy balance. Natural climate forcings include changes in the Sun's brightness, Milankovitch cycles (small variations in the shape of Earth's orbit and its axis of rotation that occur over thousands of years) and volcanic eruptions that inject light-reflecting particles as high as the stratosphere. Man-made forcings include particle pollution (aerosols) that absorb and reflect incoming sunlight; deforestation, which changes how the surface reflects and absorbs sunlight; and the rising concentration of atmospheric carbon dioxide and other greenhouse gases, which decreases the rate at which heat is radiated to space.
A forcing can trigger feedbacks that intensify (positive feedback) or weaken (negative feedback) the original forcing. For example, loss of ice at the poles, which makes them less reflective, causes greater absorption of energy and so increases the rate at which the ice melts, is an example of a positive feedback.
The observed planetary energy imbalance during the recent solar minimum shows that solar forcing of climate, although natural and significant, is overwhelmed by anthropogenic climate forcing.
In 2012, NASA scientists reported that to stop global warming atmospheric CO2 content would have to be reduced to 350 ppm or less, assuming all other climate forcings were fixed. The impact of anthropogenic aerosols has not been quantified, but individual aerosol types are thought to have substantial heating and cooling effects.
The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without this atmosphere.
Global warming potential (GWP) is a measure of how much heat a greenhouse gas traps in the atmosphere up to a specific time horizon, relative to carbon dioxide. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide and is expressed as a factor of carbon dioxide.
Climate models use quantitative methods to simulate the interactions of the important drivers of climate, including atmosphere, oceans, land surface and ice. They are used for a variety of purposes from study of the dynamics of the climate system to projections of future climate.
Cloud forcing is, in meteorology, the difference between the radiation budget components for average cloud conditions and cloud-free conditions. Much of the interest in cloud forcing relates to its role as a feedback process in the present period of global warming.
Radiative cooling is the process by which a body loses heat by thermal radiation.
A general circulation model (GCM) is a type of climate model. It employs a mathematical model of the general circulation of a planetary atmosphere or ocean. It uses the Navier–Stokes equations on a rotating sphere with thermodynamic terms for various energy sources. These equations are the basis for computer programs used to simulate the Earth's atmosphere or oceans. Atmospheric and oceanic GCMs are key components along with sea ice and land-surface components.
Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation. Particle motion results in charge-acceleration or dipole oscillation which produces electromagnetic radiation.
Radiative forcing or climate forcing is the difference between insolation (sunlight) absorbed by the Earth and energy radiated back to space. The influences that cause changes to the Earth's climate system altering Earth's radiative equilibrium, forcing temperatures to rise or fall, are called climate forcings. Positive radiative forcing means Earth receives more incoming energy from sunlight than it radiates to space. This net gain of energy will cause warming. Conversely, negative radiative forcing means that Earth loses more energy to space than it receives from the sun, which produces cooling.
This glossary of climate change is a list of definitions of terms and concepts relevant to climate change, global warming, and related topics.
This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting.
A runaway greenhouse effect is when there is enough of a greenhouse gas in a planet's atmosphere such that the gas blocks thermal radiation from the planet, preventing the planet from cooling and from having liquid water on its surface. The runaway greenhouse effect can be defined by a limit on a planet's outgoing longwave radiation which is asymptotically reached due to higher surface temperatures boiling a condensable species into the atmosphere, increasing its optical depth. This runaway positive feedback means the planet cannot cool down through longwave radiation and continues to heat up until it can radiate outside of the absorption bands of the condensable species. The runaway greenhouse effect is often formulated with water vapor as the condensable species. In this case the water vapor reaches the stratosphere and escapes into space via hydrodynamic escape, resulting in a desiccated planet. An example of this is believed to have happened in the early history of Venus.
The anti-greenhouse effect is a mechanism similar to the greenhouse effect, but with the opposite consequence of cooling the surface temperature of a planet. If gases in the atmosphere of a planet have a lesser transmittance for inbound radiation than for outbound radiation, the surface temperature at which inbound and outbound heat fluxes are at equilibrium is lower.
Outgoing Long-wave Radiation (OLR) is electromagnetic radiation of wavelengths between 3.0 and 100 µm emitted from Earth and its atmosphere out to space in the form of thermal radiation. it is also referred to as up-welling long-wave radiation and terrestrial long-wave flux, among others. The flux of energy transported by outgoing long-wave radiation is measured in W/m². In the Earth’s climate system, long-wave radiation involves processes of absorption, scattering, and emissions from atmospheric gases, aerosols, clouds and the surface.
The surface of the Sun radiates light and heat at approximately 5,500 °C. The Earth is much cooler and so radiates heat back away from itself at much longer wavelengths, mostly in the infrared range. The idealized greenhouse model is based on the fact that certain gases in the Earth's atmosphere, including carbon dioxide and water vapour, are transparent to the high-frequency, high-energy solar radiation, but are much more opaque to the lower frequency infrared radiation leaving the surface of the earth. Thus heat is easily let in, but is partially trapped by these gases as it tries to leave. Rather than get hotter and hotter, Kirchhoff's law of thermal radiation says that the gases of the atmosphere also have to re-emit the infrared energy that they absorb, and they do so, also at long infrared wavelengths, both upwards into space as well as downwards back towards the Earth's surface. In the long-term, thermal equilibrium is reached when all the heat energy arriving on the planet is leaving again at the same rate. In this idealized model, the greenhouse gases cause the surface of the planet to be warmer than it would be without them, in order for the required amount of heat energy finally to be radiated out into space from the top of the atmosphere.
A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gases cause the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone. Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F). The atmospheres of Venus, Mars and Titan also contain greenhouse gases.
The planetary equilibrium temperature is a theoretical temperature that a planet would be at when considered simply as if it were a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere is irrelevant, as the equilibrium temperature is calculated purely from a balance with incident stellar energy.
Schwarzschild's equation is used to calculate radiative transfer – energy transfer – through a medium in local thermodynamic equilibrium that both absorbs and emits electromagnetic radiation.
The skin temperature of an atmosphere is the temperature of a hypothetical thin layer high in the atmosphere that is transparent to incident solar radiation and partially absorbing of infrared radiation from the planet. It provides an approximation for the temperature of the tropopause on terrestrial planets with greenhouse gases present in their atmospheres.
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