Earth's energy budget accounts for the balance between the
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
that
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
receives from the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
and the energy the Earth loses back into
outer space
Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...
. Smaller energy sources, such as Earth's internal heat, are taken into consideration, but make a tiny contribution compared to solar energy. The energy budget also accounts for how energy moves through the
climate system
Earth's climate system is a complex system having five interacting components: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosphere (living things). '' ...
. Because the Sun heats the equatorial
tropics
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
more than the
polar regions
The polar regions, also called the frigid zones or polar zones, of Earth are the regions of the planet that surround its geographical poles (the North and South Poles), lying within the polar circles. These high latitudes are dominated by float ...
, received
solar irradiance
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/ ...
is unevenly distributed. As the energy seeks equilibrium across the planet, it drives interactions in Earth's climate system, i.e., Earth's
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
,
ice
Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
,
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
,
rocky crust, and all
living things. The result is Earth's
climate
Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...
.
Earth's energy budget depends on many factors, such as atmospheric
aerosols
An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog or mist, dust, forest exudates, and geyser steam. Examples of anthrop ...
,
greenhouse gases
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...
, the planet's surface
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
(reflectivity),
clouds
In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may com ...
, vegetation, land use patterns, and more. When the incoming and outgoing
energy flux Energy flux is the rate of transfer of energy through a surface. The quantity is defined in two different ways, depending on the context:
# Total rate of energy transfer (not per unit area); SI units: W = J⋅s−1.
# Specific rate of energy transfe ...
es are in balance, Earth is in
radiative equilibrium Radiative equilibrium is the condition where the total thermal radiation leaving an object is equal to the total thermal radiation entering it. It is one of the several requirements for thermodynamic equilibrium, but it can occur in the absence of t ...
and the climate system will be ''relatively'' stable.
Global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
occurs when earth receives more energy than it gives back to space, and
global cooling
Global cooling was a conjecture, especially during the 1970s, of imminent cooling of the Earth culminating in a period of extensive glaciation, due to the cooling effects of aerosols or orbital forcing.
Some press reports in the 1970s specul ...
takes place when the outgoing energy is greater.
Multiple types of measurements and observations show a warming imbalance since at least year 1970.
The
rate of heating from this human-caused event is without precedent.
When the energy budget changes, there is a delay before average
global surface temperature
In earth science, global surface temperature (GST; sometimes referred to as global mean surface temperature, GMST, or global average surface temperature) is calculated by averaging the temperature at the surface of the sea and air temperature ...
changes significantly. This is due to the
thermal inertia
In thermodynamics, a material's thermal effusivity, thermal inertia or thermal responsivity is a measure of its ability to exchange thermal energy with its surroundings. It is defined as the square root of the product of the material's thermal co ...
of the
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
s, land and
cryosphere
]
The cryosphere (from the Ancient Greek, Greek ''kryos'', "cold", "frost" or "ice" and ''sphaira'', "globe, ball") is an all-encompassing term for those portions of Earth's surface where water is in solid form, including sea ice, lake ice, ri ...
.
Accurate quantification of these energy flows and storage amounts is a requirement within most
climate model
Numerical 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 cl ...
s.
Earth's energy flows
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
solar insolation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
(all forms of electromagnetic radiation).
Incoming solar energy (shortwave radiation)
The total amount of energy received per second at the top of
Earth's atmosphere
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...
(TOA) is measured in
watt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
s and is given by the
solar constant
The solar constant (''GSC'') is a flux density measuring mean solar electromagnetic radiation (total solar irradiance) per unit area. It is measured on a surface perpendicular to the rays, one astronomical unit (au) from the Sun (roughly the ...
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 area of a sphere (i.e. the area of a circle), the globally and yearly averaged TOA flux is one quarter of the solar constant and so is approximately 340 watts per square
meter
The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its prefi ...
(W/m
2).
Since the absorption varies with location as well as with diurnal, seasonal and annual variations, the numbers quoted are multi-year averages obtained from multiple satellite measurements.
Of the ~340 W/m
2 of solar radiation received by the Earth, an average of ~77 W/m
2 is reflected back to space by clouds and the atmosphere and ~23 W/m
2 is reflected by the surface
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
, leaving ~240 W/m
2 of solar energy input to the Earth's energy budget. This amount is called the absorbed solar radiation (ASR). It implies a value of about 0.3 for the mean net albedo of Earth, also called its
Bond albedo
The Bond albedo (or ''spheric albedo'' or ''planetary albedo'' or ''bolometric albedo''), named after the American astronomer George Phillips Bond (1825–1865), who originally proposed it, is the fraction of power in the total electromagnetic rad ...
(A):
:
Outgoing longwave radiation
Outgoing longwave radiation (OLR) is usually defined as outgoing energy leaving the planet, most of which is in the
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
band
Band or BAND may refer to:
Places
*Bánd, a village in Hungary
*Band, Iran, a village in Urmia County, West Azerbaijan Province, Iran
*Band, Mureș, a commune in Romania
* Band-e Majid Khan, a village in Bukan County, West Azerbaijan Province, I ...
. Generally, absorbed solar energy is converted to different forms of heat energy. Some of this energy is emitted as OLR directly to space, while the rest is first transported through the climate system as radiant and other forms of thermal energy. For example, indirect emissions occur following heat transport from the planet's surface layers (land and ocean) to the atmosphere via
evapotranspiration
Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transpi ...
and
latent heat
Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition.
Latent heat can be understo ...
fluxes or
conduction
Conductor or conduction may refer to:
Music
* Conductor (music), a person who leads a musical ensemble, such as an orchestra.
* Conductor (album), ''Conductor'' (album), an album by indie rock band The Comas
* Conduction, a type of structured f ...
/
convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
processes.
Ultimately, all of outgoing energy is radiated in the form of longwave radiation back into space.
The transport of OLR from Earth's surface through its multi-layered atmosphere follows
Kirchoff's law of thermal radiation
In heat transfer, Kirchhoff's law of thermal radiation refers to wavelength-specific radiative emission and absorption by a material body in thermodynamic equilibrium, including radiative exchange equilibrium. It is a special case of Onsage ...
. A
one-layer model produces an approximate description of OLR which yields temperatures at the surface (T
s=288
Kelvin
The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...
) and at the middle of the
troposphere
The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
(T
a=242 Kelvin) that are close to observed average values:
:
In this expression σ is the
Stefan-Boltzmann constant and ε represents the
emissivity
The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is n ...
of the atmosphere. Aerosols, clouds, water vapor, and trace greenhouse gases contribute to an average value of about ε=0.78. The strong (fourth-power) temperature sensitivity acts to help maintain a near-balance of the outgoing energy flow to the incoming flow via small changes in the planet's
absolute temperature
Thermodynamic temperature is a quantity defined in thermodynamics as distinct from kinetic theory or statistical mechanics.
Historically, thermodynamic temperature was defined by Kelvin in terms of a macroscopic relation between thermodynamic wor ...
s.
Earth's internal heat sources and other small effects
The
geothermal heat flow from the Earth's interior is estimated to be 47
terawatt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wat ...
s (TW)
and split approximately equally between
radiogenic
A radiogenic nuclide is a nuclide that is produced by a process of radioactive decay. It may itself be radioactive (a radionuclide) or stable (a stable nuclide).
Radiogenic nuclides (more commonly referred to as radiogenic isotopes) form some of ...
heat and heat left over from the Earth's formation. This corresponds to an average flux of 0.087 W/m
2 and represents only 0.027% of Earth's total energy budget at the surface, being dwarfed by the 173,000 TW of incoming
solar radiation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
.
Human production of energy is even lower at an estimated 160,000 TW-hr for all of year 2019. This corresponds to an average continuous heat flow of about 18 TW.
However, consumption is growing rapidly and energy production with fossil fuels also produces an increase in atmospheric greenhouse gases, leading to a more than 20 times larger
imbalance
A balance disorder is a disturbance that causes an individual to feel unsteady, for example when standing or walking. It may be accompanied by feelings of giddiness, or wooziness, or having a sensation of movement, spinning, or floating. Balance ...
in the incoming/outgoing flows that originate from solar radiation.
Photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
also has a significant effect: An estimated 140 TW (or around 0.08%) of incident energy gets captured by photosynthesis, giving energy to plants to produce
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
.
A similar flow of thermal energy is released over the course of a year when plants are used as food or fuel.
Other minor sources of energy are usually ignored in the calculations, including accretion of
interplanetary dust
The interplanetary dust cloud, or zodiacal cloud (as the source of the zodiacal light), consists of cosmic dust (small particles floating in outer space) that pervades the space between planets within planetary systems, such as the Solar System. ...
and
solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
, light from stars other than the Sun and the thermal radiation from space. Earlier,
Joseph Fourier
Jean-Baptiste Joseph Fourier (; ; 21 March 1768 – 16 May 1830) was a French people, French mathematician and physicist born in Auxerre and best known for initiating the investigation of Fourier series, which eventually developed into Fourier an ...
had claimed that deep space radiation was significant in a paper often cited as the first on the
greenhouse effect
The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...
.
Budget analysis
![Earth_heat_balance_Sankey_diagram](https://upload.wikimedia.org/wikipedia/commons/2/29/Earth_heat_balance_Sankey_diagram.svg)
In simplest terms, Earth's energy budget is balanced when the incoming flow equals the outgoing flow. Since a portion of incoming energy is directly reflected, the balance can also be stated as absorbed incoming solar (shortwave) radiation equal to outgoing longwave radiation:
:
Internal flow analysis
To describe some of the internal flows within the budget, let the insolation received at the top of the atmosphere be 100 units (=340 W/m
2), as shown in the accompanying Sankey diagram. Called the
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
of Earth, around 35 units in this example are directly 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 (ASR=220 W/m
2) are absorbed: 14 within the atmosphere and 51 by the Earth's surface.
The 51 units reaching and absorbed by the surface are emitted back to space through various forms of terrestrial energy: 17 directly radiated to space and 34 absorbed by the atmosphere (19 through
latent heat of vaporisation
The enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. T ...
, 9 via convection and turbulence, and 6 as absorbed infrared by
greenhouse gases
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...
). The 48 units absorbed by the atmosphere (34 units from terrestrial energy and 14 from insolation) are then finally radiated back to space. This simplified example neglects some details of mechanisms that recirculate, store, and thus lead to further buildup of heat near the surface.
Ultimately the 65 units (17 from the ground and 48 from the atmosphere) are emitted as OLR. They approximately balance the 65 units (ASR) absorbed from the sun in order to maintain a net-zero gain of energy by Earth.
Role of the greenhouse effect
![Greenhouse Effect](https://upload.wikimedia.org/wikipedia/commons/c/cd/Greenhouse_effect.svg)
The major
atmospheric
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
gases (
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
and
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
) are transparent to incoming sunlight but are also transparent to outgoing longwave (thermal/infrared) radiation. However,
water vapor
(99.9839 °C)
, -
, Boiling point
,
, -
, specific gas constant
, 461.5 J/( kg·K)
, -
, Heat of vaporization
, 2.27 MJ/kg
, -
, Heat capacity
, 1.864 kJ/(kg·K)
Water vapor, water vapour or aqueous vapor is the gaseous pha ...
,
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
,
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
and other trace gases are opaque to many
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
s of thermal radiation.
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
Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
, and at roughly 5–6
kilometre
The kilometre ( SI symbol: km; or ), spelt kilometer in American English, is a unit of length in the International System of Units (SI), equal to one thousand metres (kilo- being the SI prefix for ). It is now the measurement unit used for ex ...
s, 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. Earth's
in-situ surface temperatures are thus higher than they would be if governed 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 longwave infrared radiation leaves.
As viewed from Earth's surrounding space, greenhouse gases influence the planet's atmospheric
emissivity
The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is n ...
(ε). Changes in atmospheric composition can thus shift the overall radiation balance. For example, an increase in heat trapping by a growing concentration of greenhouse gases (i.e. an ''enhanced greenhouse effect'') forces a decrease in OLR and a warming (restorative) energy imbalance. Ultimately when the amount of greenhouse gases increases or decreases, in-situ surface temperatures rise or fall until the ASR = OLR balance is again achieved.
Heat storage reservoirs
![Earth's Heat Accumulation](https://upload.wikimedia.org/wikipedia/commons/5/59/Earth%27s_Heat_Accumulation.png)
Land, ice, and oceans are active material constituents of Earth's climate system along with the atmosphere. They have far greater mass and
heat capacity
Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K).
Heat capacity i ...
, and thus much more
thermal inertia
In thermodynamics, a material's thermal effusivity, thermal inertia or thermal responsivity is a measure of its ability to exchange thermal energy with its surroundings. It is defined as the square root of the product of the material's thermal co ...
. When radiation is directly absorbed or the surface temperature changes,
thermal energy
The term "thermal energy" is used loosely in various contexts in physics and engineering. It can refer to several different well-defined physical concepts. These include the internal energy or enthalpy of a body of matter and radiation; heat, d ...
will flow as
sensible heat
Sensible heat is heat exchanged by a body or thermodynamic system in which the exchange of heat changes the temperature of the body or system, and some macroscopic variables of the body or system, but leaves unchanged certain other macroscopic vari ...
either into or out of the bulk mass of these components via conduction/convection
heat transfer
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...
processes. The transformation of water between its solid/liquid/vapor states also acts as a source or sink of
potential energy
In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors.
Common types of potential energy include the gravitational potentia ...
in the form of
latent heat
Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition.
Latent heat can be understo ...
. These processes buffer the surface conditions against some of the rapid radiative changes in the atmosphere. As a result, the daytime versus nighttime difference in surface temperatures is relatively small. Likewise, Earth's climate system as a whole shows a delayed response to shifts in the atmospheric radiation balance.
The top few meters of Earth's oceans harbor more thermal energy than its entire atmosphere.
Like atmospheric gases,
fluidic
Fluidics, or fluidic logic, is the use of a fluid to perform analog or digital operations similar to those performed with electronics.
The physical basis of fluidics is pneumatics and hydraulics, based on the theoretical foundation of fluid ...
ocean waters transport vast amounts of such energy over the planet's surface. Sensible heat also moves into and out of great depths under conditions that favor
downwelling
Downwelling is the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air. It is the ''sinking'' limb of a convecti ...
or
upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutr ...
.
Over 90 percent of the extra energy that has accumulated on Earth from ongoing global warming since 1970 has been
stored in the ocean.
[ About one-third has propagated to depths below 700 meters. The overall rate of growth has also risen during recent decades, reaching close to 500 TW (1 W/m2) as of 2020.] That led to about 14 zettajoules (ZJ) of heat gain for the year, exceeding the 570 exajoules (=160,000 TW-hr) of total primary energy consumed by humans by a factor of at least 20.
Heating/cooling rate analysis
Generally speaking, changes to Earth's energy flux balance can be thought of as being the result of external forcings (both natural and anthropogenic, radiative and non-radiative), system feedbacks, and internal system variability. Such changes are primarily expressed as observable shifts in temperature (T), clouds (C), water vapor (W), aerosols (A), trace greenhouse gases (G), land/ocean/ice surface reflectance (S), and as minor shifts in insolaton (I) among other possible factors. Earth's heating/cooling rate can then be analyzed over selected timeframes (Δt) as the net change in energy (ΔE) associated with these attributes:
:
Here the term ΔET is negative-valued when temperature rises due to the strong direct influence on OLR.
The recent increase in trace greenhouse gases produces an enhanced greenhouse effect, and thus a positive ΔEG forcing term. By contrast, a large volcanic eruption (e.g. Mount Pinatubo 1991, El Chichón
El Chichón, also known as Chichonal, is an active volcano in Francisco León, Chiapas, Francisco León, north-western Chiapas, Mexico. El Chichón is part of a geologic zone known as the Chiapanecan Volcanic Arc. El Chichón is a complex of dome ...
1982) can inject sulfur-containing compounds into the upper atmosphere. High concentrations of stratospheric sulfur aerosols Stratospheric sulfur aerosols are sulfur-rich particles which exist in the stratosphere region of the Earth's atmosphere. The layer of the atmosphere in which they exist is known as the Junge layer, or simply the stratospheric aerosol layer. These p ...
may persist for up to a few years, yielding a negative forcing contribution to ΔEA. Various other types of anthropogenic aerosol emissions make both positive and negative contributions to ΔEA. Solar cycle
The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfa ...
s produce ΔEI smaller in magnitude than those of recent ΔEG trends from human activity.
Climate forcings are complex since they can produce direct and indirect feedback
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled ...
s that intensify (positive feedback
Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the ...
) or weaken (negative feedback
Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, whether caused by ...
) the original forcing. These often follow the temperature response. Water vapor trends as a positive feedback with respect to temperature changes due to evaporation shifts and the Clausius-Clapeyron relation. An increase in water vapor results in positive ΔEW due to further enhancement of the greenhouse effect. A slower positive feedback is the ice-albedo feedback. For example, the loss of Arctic ice due to rising temperatures makes the region less reflective, leading to greater absorption of energy and even faster ice melt rates, thus positive influence on ΔES. Collectively, feedbacks tend to amplify global warming or cooling.
Clouds are responsible for about half of Earth's albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
and are powerful expressions of internal variability of the climate system. They may also act as feedbacks to forcings, and could be forcings themselves if for example a result of cloud seeding
Cloud seeding is a type of weather modification that aims to change the amount or type of precipitation that falls from clouds by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical p ...
activity. Contributions to ΔEC vary regionally and depending upon cloud type. Measurements from satellites are gathered in concert with simulations from models in the effort to improve understanding and reduce uncertainty.
Earth's energy imbalance
If Earth's incoming energy flux is larger or smaller than the outgoing energy flux, then the planet will gain (warm) or lose (cool) net heat energy in accordance with the law of energy conservation
In physics and chemistry, the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be Conservation law, ''conserved'' over time. This law, first proposed and tested by Émilie du Chât ...
:
:
When Earth's energy imbalance (EEI) shifts by a sufficiently large amount, it is directly measurable by orbiting satellite-based radiometric instruments. Imbalances which fail to reverse over time will also drive long-term temperature changes in the atmospheric, oceanic, land, and ice components of the climate system
Earth's climate system is a complex system having five interacting components: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosphere (living things). '' ...
. In situ temperature changes and related effects thus provide indirect measures of EEI. From mid-2005 to mid-2019, satellite and ocean temperature observations have each independently shown an approximate doubling of the (global) warming imbalance in Earth's energy budget.
Direct measurement
Several satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...
s directly measure the energy absorbed and radiated by Earth, and thus by inference the energy imbalance. The NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
Earth Radiation Budget Experiment
The Earth Radiation Budget Satellite (ERBS) is a NASA scientific research satellite within NASA's ERBE (Earth Radiation Budget Experiment) Research Program - a three-satellite mission, designed to investigate the Earth radiation budget. It also ...
(ERBE) project involves three such satellites: the Earth Radiation Budget Satellite
The Earth Radiation Budget Satellite (ERBS) is a NASA scientific research satellite within NASA's ERBE (Earth Radiation Budget Experiment) Research Program - a three-satellite mission, designed to investigate the Earth radiation budget. It also ...
(ERBS), launched October 1984; NOAA-9, launched December 1984; and NOAA-10, launched September 1986.
NASA's Clouds and the Earth's Radiant Energy System
Clouds and the Earth's Radiant Energy System (CERES) is NASA climatological experiment from Earth orbit. The CERES are scientific satellite instruments, part of the NASA's Earth Observing System (EOS), designed to measure both solar-reflected an ...
(CERES) instruments are part of its Earth Observing System
The Earth Observing System (EOS) is a program of NASA comprising a series of artificial satellite missions and scientific instruments in Earth orbit designed for long-term global observations of the land surface, biosphere, atmosphere, and oceans ...
(EOS) since 1998. CERES is designed to measure both solar-reflected (short wavelength) and Earth-emitted (long wavelength) radiation. Analysis of CERES data by its principal investigators showed an increasing trend in EEI from in 2005 to in 2019. Contributing factors included more water vapor, less clouds, increasing greenhouse gases, and declining ice that were partially offset by rising temperatures. Subsequent investigation of the behavior using the GFDL
The GNU Free Documentation License (GNU FDL or simply GFDL) is a copyleft license for free documentation, designed by the Free Software Foundation (FSF) for the GNU Project. It is similar to the GNU General Public License, giving readers the r ...
CM4/AM4 climate model
Numerical 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 cl ...
concluded there was a less than 1% chance that internal climate variability alone caused the trend.
Other researchers have used data from CERES, AIRS, CloudSat
CloudSat is a NASA Earth observation satellite, which was launched on a Delta II rocket on April 28, 2006. It uses radar to measure the altitude and properties of clouds, adding to information on the relationship between clouds and climate in ord ...
, and other EOS instruments to look for trends of radiative forcing
Radiative forcing (or climate forcing) is the change in energy flux in the atmosphere caused by natural or anthropogenic factors of climate change as measured by watts / metre2. It is a scientific concept used to quantify and compare the external ...
embedded within the EEI data. Their analysis showed a forcing rise of from years 2003 to 2018. About 80% of the increase was associated with the rising concentration of greenhouse gases
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...
which reduced the outgoing longwave radiation.
Further satellite measurements including TRMM
The Tropical Rainfall Measuring Mission (TRMM) was a joint space mission between NASA and JAXA designed to monitor and study tropical rainfall. The term refers to both the mission itself and the satellite that the mission used to collect data. ...
and CALIPSO
CALIPSO is a joint NASA (USA) and CNES (France) environmental satellite, built in the Cannes Mandelieu Space Center, which was launched atop a Delta II rocket on April 28, 2006. Its name stands for Cloud-Aerosol Lidar and Infrared Pathfinder Sate ...
data have indicated additional precipitation, which is sustained by increased energy leaving the surface through evaporation (the latent heat flux), offsetting some of the increase in the longwave greenhouse flux to the surface.
It is noteworthy that radiometric calibration
Radiometric calibration is a general term used in science and technology for any set of calibration techniques in support of the measurement of electromagnetic radiation and atomic particle radiation. These can be for instance, in the field of rad ...
uncertainties limit the capability of the current generation of satellite-based instruments, which are otherwise stable and precise. As a result, relative changes in EEI are quantifiable with an accuracy
Accuracy and precision are two measures of ''observational error''.
''Accuracy'' is how close a given set of measurements (observations or readings) are to their ''true value'', while ''precision'' is how close the measurements are to each other ...
which is not also achievable for any single measurement of the absolute imbalance.
In situ measurements
Global surface temperature (GST) is calculated by averaging temperatures measured at the surface of the sea along with air temperatures measured over land. Reliable data extending to at least 1880 shows that GST has undergone a steady increase of about 0.18°C per decade since about year 1970.
Ocean waters are especially effective absorbents of solar energy and have far greater total heat capacity
Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K).
Heat capacity i ...
than the atmosphere. Research vessels and stations have sampled sea temperatures at depth and around the globe since before 1960. Additionally after year 2000, an expanding network of over 3000 Argo robotic floats has measured the temperature anomaly, or equivalently the change in ocean heat content (OHC). Since at least 1990, OHC has increased at a steady or accelerating rate. Changes in OHC provide the most robust indirect measure of EEI since the oceans take up 90% of the excess heat.
The extent of floating and grounded ice is measured by satellites, while the change in mass is then inferred from measured changes in sea level in concert with computational models that account for thermal expansion and other factors. Observations since 1994 show that ice has retreated from every part of Earth at an accelerating rate.
Importance as a climate change metric
Climate researchers Kevin Trenberth
Kevin Edward Trenberth (born 8 November 1944) is part of the Climate Analysis Section at the US NCAR National Center for Atmospheric Research. He was a lead author of the 2001 and 2007 IPCC Scientific Assessment of Climate Change (see IPCC Fourt ...
, James Hansen
James Edward Hansen (born March 29, 1942) is an American adjunct professor directing the Program on Climate Science, Awareness and Solutions of the Earth Institute at Columbia University. He is best known for his research in climatology, his 1 ...
, and colleagues have identified the monitoring of Earth's energy imbalance as an imperative to help policymakers guide the pace of planning for climate change adaptation
Climate change adaptation is the process of adjusting to current or expected effects of climate change.IPCC, 2022Annex II: Glossary öller, V., R. van Diemen, J.B.R. Matthews, C. Méndez, S. Semenov, J.S. Fuglestvedt, A. Reisinger (eds.) InClimat ...
. Because of climate system inertia, longer-term EEI trends can forecast further changes that are "in the pipeline".
In 2012, NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
scientists reported that to stop global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
atmospheric CO2 concentration would have to be reduced to 350 ppm or less, assuming all other climate forcings were fixed. As of 2020, atmospheric CO2 reached 415 ppm and all long-lived greenhouse gases exceeded a 500 ppm -equivalent concentration due to continued growth in human emissions.
See also
* Lorenz energy cycle The Lorenz energy cycle describes the generation, conversion and dissipation of energy in the general atmospheric circulation. It is named after the meteorologist Edward N. Lorenz who worked on its mathematical formulation in the 1950s.
Descrip ...
* Planetary equilibrium temperature
The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is ...
* Climate sensitivity
Climate sensitivity is a measure of how much Earth's surface will cool or warm after a specified factor causes a change in its climate system, such as how much it will warm for a doubling in the atmospheric carbon dioxide () concentration. In te ...
* Tipping points in the climate system
In climate science, a tipping point is a critical threshold that, when crossed, leads to large and often irreversible changes in the climate system. If tipping points are crossed, they are likely to have severe impacts on human society. Tippin ...
* Anthropogenic metabolism Anthropogenic metabolism, also referred to as metabolism of the anthroposphere, is a term used in industrial ecology, material flow analysis, and waste management to describe the material and energy turnover of human society. It emerges from the app ...
*
References
Additional bibliography for cited sources
IPCC reports
AR5 Working Group I Report
* (pb: ).
**
Special Report on Global Warming of 1.5 °C
*
Global Warming of 1.5 ºC —
**
**
AR6 Working Group I Report
*
**
**
**
External links
NASA: The Atmosphere's Energy Budget
Clouds and Earth's Radiant Energy System (CERES)
NASA/GEWEX Surface Radiation Budget (SRB) Project
{{DEFAULTSORT:Earth's Energy Budget
Atmospheric sciences
Climate forcing
Climate variability and change
Climatology
Earth
Earth sciences
Energy
Environmental science
Oceanography
Articles containing video clips