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Earth's average surface temperature due to its albedo and the greenhouse effect is currently about .[SEP]If Earth were frozen entirely (and hence be more reflective), the average temperature of the planet would drop below .

If Earth were frozen entirely (and hence be more reflective), the average temperature of the planet would drop below .[SEP]If only the continental land masses became covered by glaciers, the mean temperature of the planet would drop to about .

If only the continental land masses became covered by glaciers, the mean temperature of the planet would drop to about .[SEP]In contrast, if the entire Earth was covered by water – a so-called ocean planet – the average temperature on the planet would rise to almost .

In contrast, if the entire Earth was covered by water – a so-called ocean planet – the average temperature on the planet would rise to almost .[SEP]In 2021, scientists reported that Earth dimmed by ~0.5% over two decades (1998-2017) as measured by earthshine using modern photometric techniques.

In 2021, scientists reported that Earth dimmed by ~0.5% over two decades (1998-2017) as measured by earthshine using modern photometric techniques.[SEP]This may have both been co-caused by climate change as well as a substantial increase in global warming.

This may have both been co-caused by climate change as well as a substantial increase in global warming.[SEP]However, the link to climate change has not been explored to date and it is unclear whether or not this represents an ongoing trend.

However, the link to climate change has not been explored to date and it is unclear whether or not this represents an ongoing trend.[SEP]White-sky, black-sky, and blue-sky albedo For land surfaces, it has been shown that the albedo at a particular solar zenith angle θi can be approximated by the proportionate sum of two terms: the directional-hemispherical reflectance at that solar zenith angle, , sometimes referred to as black-sky albedo, and the bi-hemispherical reflectance, , sometimes referred to as white-sky albedo.

White-sky, black-sky, and blue-sky albedo For land surfaces, it has been shown that the albedo at a particular solar zenith angle θi can be approximated by the proportionate sum of two terms: the directional-hemispherical reflectance at that solar zenith angle, , sometimes referred to as black-sky albedo, and the bi-hemispherical reflectance, , sometimes referred to as white-sky albedo.[SEP]with being the proportion of direct radiation from a given solar angle, and being the proportion of diffuse illumination, the actual albedo (also called blue-sky albedo) can then be given as:

with being the proportion of direct radiation from a given solar angle, and being the proportion of diffuse illumination, the actual albedo (also called blue-sky albedo) can then be given as:[SEP]This formula is important because it allows the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface.

This formula is important because it allows the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface.[SEP]Examples of terrestrial albedo effects

Examples of terrestrial albedo effects[SEP]Illumination Albedo is not directly dependent on illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth's surface at that location (e.g. through melting of reflective ice).

Illumination Albedo is not directly dependent on illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth's surface at that location (e.g. through melting of reflective ice).[SEP]That said, albedo and illumination both vary by latitude.

That said, albedo and illumination both vary by latitude.[SEP]Albedo is highest near the poles and lowest in the subtropics, with a local maximum in the tropics.

Albedo is highest near the poles and lowest in the subtropics, with a local maximum in the tropics.[SEP]Insolation effects The intensity of albedo temperature effects depends on the amount of albedo and the level of local insolation (solar irradiance); high albedo areas in the Arctic and Antarctic regions are cold due to low insolation, whereas areas such as the Sahara Desert, which also have a relatively high albedo, will be hotter due to high insolation.

Insolation effects The intensity of albedo temperature effects depends on the amount of albedo and the level of local insolation (solar irradiance); high albedo areas in the Arctic and Antarctic regions are cold due to low insolation, whereas areas such as the Sahara Desert, which also have a relatively high albedo, will be hotter due to high insolation.[SEP]Tropical and sub-tropical rainforest areas have low albedo, and are much hotter than their temperate forest counterparts, which have lower insolation.

Tropical and sub-tropical rainforest areas have low albedo, and are much hotter than their temperate forest counterparts, which have lower insolation.[SEP]Because insolation plays such a big role in the heating and cooling effects of albedo, high insolation areas like the tropics will tend to show a more pronounced fluctuation in local temperature when local albedo changes.

Because insolation plays such a big role in the heating and cooling effects of albedo, high insolation areas like the tropics will tend to show a more pronounced fluctuation in local temperature when local albedo changes.[SEP]Arctic regions notably release more heat back into space than what they absorb, effectively cooling the Earth.

Arctic regions notably release more heat back into space than what they absorb, effectively cooling the Earth.[SEP]This has been a concern since arctic ice and snow has been melting at higher rates due to higher temperatures, creating regions in the arctic that are notably darker (being water or ground which is darker color) and reflects less heat back into space.

This has been a concern since arctic ice and snow has been melting at higher rates due to higher temperatures, creating regions in the arctic that are notably darker (being water or ground which is darker color) and reflects less heat back into space.[SEP]This feedback loop results in a reduced albedo effect.

This feedback loop results in a reduced albedo effect.[SEP]Climate and weather Albedo affects climate by determining how much radiation a planet absorbs.

Climate and weather Albedo affects climate by determining how much radiation a planet absorbs.[SEP]The uneven heating of Earth from albedo variations between land, ice, or ocean surfaces can drive weather.

The uneven heating of Earth from albedo variations between land, ice, or ocean surfaces can drive weather.[SEP]Albedo–temperature feedback When an area's albedo changes due to snowfall, a snow–temperature feedback results.

Albedo–temperature feedback When an area's albedo changes due to snowfall, a snow–temperature feedback results.[SEP]A layer of snowfall increases local albedo, reflecting away sunlight, leading to local cooling.

A layer of snowfall increases local albedo, reflecting away sunlight, leading to local cooling.[SEP]In principle, if no outside temperature change affects this area (e.g., a warm air mass), the raised albedo and lower temperature would maintain the current snow and invite further snowfall, deepening the snow–temperature feedback.

In principle, if no outside temperature change affects this area (e.g., a warm air mass), the raised albedo and lower temperature would maintain the current snow and invite further snowfall, deepening the snow–temperature feedback.[SEP]However, because local weather is dynamic due to the change of seasons, eventually warm air masses and a more direct angle of sunlight (higher insolation) cause melting.

However, because local weather is dynamic due to the change of seasons, eventually warm air masses and a more direct angle of sunlight (higher insolation) cause melting.[SEP]When the melted area reveals surfaces with lower albedo, such as grass, soil, or ocean, the effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating.

When the melted area reveals surfaces with lower albedo, such as grass, soil, or ocean, the effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating.[SEP]Snow Snow albedo is highly variable, ranging from as high as 0.9 for freshly fallen snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow.

Snow Snow albedo is highly variable, ranging from as high as 0.9 for freshly fallen snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow.[SEP]Over Antarctica snow albedo averages a little more than 0.8.

Over Antarctica snow albedo averages a little more than 0.8.[SEP]If a marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt because more radiation is being absorbed by the snowpack (the ice–albedo positive feedback).

If a marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt because more radiation is being absorbed by the snowpack (the ice–albedo positive feedback).[SEP]Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water.

Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water.[SEP]Sea water absorbs more solar radiation than would the same surface covered with reflective snow.

Sea water absorbs more solar radiation than would the same surface covered with reflective snow.[SEP]When sea ice melts, either due to a rise in sea temperature or in response to increased solar radiation from above, the snow-covered surface is reduced, and more surface of sea water is exposed, so the rate of energy absorption increases.

When sea ice melts, either due to a rise in sea temperature or in response to increased solar radiation from above, the snow-covered surface is reduced, and more surface of sea water is exposed, so the rate of energy absorption increases.[SEP]The extra absorbed energy heats the sea water, which in turn increases the rate at which sea ice melts.

The extra absorbed energy heats the sea water, which in turn increases the rate at which sea ice melts.[SEP]As with the preceding example of snowmelt, the process of melting of sea ice is thus another example of a positive feedback.

As with the preceding example of snowmelt, the process of melting of sea ice is thus another example of a positive feedback.[SEP]Both positive feedback loops have long been recognized as important for global warming.

Both positive feedback loops have long been recognized as important for global warming.[SEP]Cryoconite, powdery windblown dust containing soot, sometimes reduces albedo on glaciers and ice sheets.

Cryoconite, powdery windblown dust containing soot, sometimes reduces albedo on glaciers and ice sheets.[SEP]The dynamical nature of albedo in response to positive feedback, together with the effects of small errors in the measurement of albedo, can lead to large errors in energy estimates.

The dynamical nature of albedo in response to positive feedback, together with the effects of small errors in the measurement of albedo, can lead to large errors in energy estimates.[SEP]Because of this, in order to reduce the error of energy estimates, it is important to measure the albedo of snow-covered areas through remote sensing techniques rather than applying a single value for albedo over broad regions.

Because of this, in order to reduce the error of energy estimates, it is important to measure the albedo of snow-covered areas through remote sensing techniques rather than applying a single value for albedo over broad regions.[SEP]Small-scale effects Albedo works on a smaller scale, too.

Small-scale effects Albedo works on a smaller scale, too.[SEP]In sunlight, dark clothes absorb more heat and light-coloured clothes reflect it better, thus allowing some control over body temperature by exploiting the albedo effect of the colour of external clothing.

In sunlight, dark clothes absorb more heat and light-coloured clothes reflect it better, thus allowing some control over body temperature by exploiting the albedo effect of the colour of external clothing.[SEP]Solar photovoltaic effects Albedo can affect the electrical energy output of solar photovoltaic devices.

Solar photovoltaic effects Albedo can affect the electrical energy output of solar photovoltaic devices.[SEP]For example, the effects of a spectrally responsive albedo are illustrated by the differences between the spectrally weighted albedo of solar photovoltaic technology based on hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si)-based compared to traditional spectral-integrated albedo predictions.

For example, the effects of a spectrally responsive albedo are illustrated by the differences between the spectrally weighted albedo of solar photovoltaic technology based on hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si)-based compared to traditional spectral-integrated albedo predictions.[SEP]Research showed impacts of over 10%.

Research showed impacts of over 10%.[SEP]More recently, the analysis was extended to the effects of spectral bias due to the specular reflectivity of 22 commonly occurring surface materials (both human-made and natural) and analyzes the albedo effects on the performance of seven photovoltaic materials covering three common photovoltaic system topologies: industrial (solar farms), commercial flat rooftops and residential pitched-roof applications.

More recently, the analysis was extended to the effects of spectral bias due to the specular reflectivity of 22 commonly occurring surface materials (both human-made and natural) and analyzes the albedo effects on the performance of seven photovoltaic materials covering three common photovoltaic system topologies: industrial (solar farms), commercial flat rooftops and residential pitched-roof applications.[SEP]Trees Because forests generally have a low albedo, (the majority of the ultraviolet and visible spectrum is absorbed through photosynthesis), some scientists have suggested that greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate impacts of deforestation).

Trees Because forests generally have a low albedo, (the majority of the ultraviolet and visible spectrum is absorbed through photosynthesis), some scientists have suggested that greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate impacts of deforestation).[SEP]In the case of evergreen forests with seasonal snow cover albedo reduction may be great enough for deforestation to cause a net cooling effect.

In the case of evergreen forests with seasonal snow cover albedo reduction may be great enough for deforestation to cause a net cooling effect.[SEP]Trees also impact climate in extremely complicated ways through evapotranspiration.

Trees also impact climate in extremely complicated ways through evapotranspiration.[SEP]The water vapor causes cooling on the land surface, causes heating where it condenses, acts a strong greenhouse gas, and can increase albedo when it condenses into clouds.

The water vapor causes cooling on the land surface, causes heating where it condenses, acts a strong greenhouse gas, and can increase albedo when it condenses into clouds.[SEP]Scientists generally treat evapotranspiration as a net cooling impact, and the net climate impact of albedo and evapotranspiration changes from deforestation depends greatly on local climate.

Scientists generally treat evapotranspiration as a net cooling impact, and the net climate impact of albedo and evapotranspiration changes from deforestation depends greatly on local climate.[SEP]In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily.

In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily.[SEP]Deciduous trees have an albedo value of about 0.15 to 0.18 whereas coniferous trees have a value of about 0.09 to 0.15.

Deciduous trees have an albedo value of about 0.15 to 0.18 whereas coniferous trees have a value of about 0.09 to 0.15.[SEP]Variation in summer albedo across both forest types is associated with maximum rates of photosynthesis because plants with high growth capacity display a greater fraction of their foliage for direct interception of incoming radiation in the upper canopy.

Variation in summer albedo across both forest types is associated with maximum rates of photosynthesis because plants with high growth capacity display a greater fraction of their foliage for direct interception of incoming radiation in the upper canopy.[SEP]The result is that wavelengths of light not used in photosynthesis are more likely to be reflected back to space rather than being absorbed by other surfaces lower in the canopy.

The result is that wavelengths of light not used in photosynthesis are more likely to be reflected back to space rather than being absorbed by other surfaces lower in the canopy.[SEP]Studies by the Hadley Centre have investigated the relative (generally warming) effect of albedo change and (cooling) effect of carbon sequestration on planting forests.

Studies by the Hadley Centre have investigated the relative (generally warming) effect of albedo change and (cooling) effect of carbon sequestration on planting forests.[SEP]They found that new forests in tropical and midlatitude areas tended to cool; new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming.

They found that new forests in tropical and midlatitude areas tended to cool; new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming.[SEP]Water reflects light very differently from typical terrestrial materials.

Water reflects light very differently from typical terrestrial materials.[SEP]The reflectivity of a water surface is calculated using the Fresnel equations.

The reflectivity of a water surface is calculated using the Fresnel equations.[SEP]At the scale of the wavelength of light even wavy water is always smooth so the light is reflected in a locally specular manner (not diffusely).

At the scale of the wavelength of light even wavy water is always smooth so the light is reflected in a locally specular manner (not diffusely).[SEP]The glint of light off water is a commonplace effect of this.

The glint of light off water is a commonplace effect of this.[SEP]At small angles of incident light, waviness results in reduced reflectivity because of the steepness of the reflectivity-vs.-incident-angle curve and a locally increased average incident angle.

At small angles of incident light, waviness results in reduced reflectivity because of the steepness of the reflectivity-vs.-incident-angle curve and a locally increased average incident angle.[SEP]Although the reflectivity of water is very low at low and medium angles of incident light, it becomes very high at high angles of incident light such as those that occur on the illuminated side of Earth near the terminator (early morning, late afternoon, and near the poles).

Although the reflectivity of water is very low at low and medium angles of incident light, it becomes very high at high angles of incident light such as those that occur on the illuminated side of Earth near the terminator (early morning, late afternoon, and near the poles).[SEP]However, as mentioned above, waviness causes an appreciable reduction.

However, as mentioned above, waviness causes an appreciable reduction.[SEP]Because light specularly reflected from water does not usually reach the viewer, water is usually considered to have a very low albedo in spite of its high reflectivity at high angles of incident light.

Because light specularly reflected from water does not usually reach the viewer, water is usually considered to have a very low albedo in spite of its high reflectivity at high angles of incident light.[SEP]Note that white caps on waves look white (and have high albedo) because the water is foamed up, so there are many superimposed bubble surfaces which reflect, adding up their reflectivities.

Note that white caps on waves look white (and have high albedo) because the water is foamed up, so there are many superimposed bubble surfaces which reflect, adding up their reflectivities.[SEP]Fresh 'black' ice exhibits Fresnel reflection.

Fresh 'black' ice exhibits Fresnel reflection.[SEP]Snow on top of this sea ice increases the albedo to 0.9.

Snow on top of this sea ice increases the albedo to 0.9.[SEP]Clouds Cloud albedo has substantial influence over atmospheric temperatures.

Clouds Cloud albedo has substantial influence over atmospheric temperatures.[SEP]Different types of clouds exhibit different reflectivity, theoretically ranging in albedo from a minimum of near 0 to a maximum approaching 0.8.

Different types of clouds exhibit different reflectivity, theoretically ranging in albedo from a minimum of near 0 to a maximum approaching 0.8.[SEP]On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water.

On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water.[SEP]Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth."

Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth."[SEP]Albedo and climate in some areas are affected by artificial clouds, such as those created by the contrails of heavy commercial airliner traffic.

Albedo and climate in some areas are affected by artificial clouds, such as those created by the contrails of heavy commercial airliner traffic.[SEP]A study following the burning of the Kuwaiti oil fields during Iraqi occupation showed that temperatures under the burning oil fires were as much as colder than temperatures several miles away under clear skies.

A study following the burning of the Kuwaiti oil fields during Iraqi occupation showed that temperatures under the burning oil fires were as much as colder than temperatures several miles away under clear skies.[SEP]Aerosol effects Aerosols (very fine particles/droplets in the atmosphere) have both direct and indirect effects on Earth's radiative balance.

Aerosol effects Aerosols (very fine particles/droplets in the atmosphere) have both direct and indirect effects on Earth's radiative balance.[SEP]The direct (albedo) effect is generally to cool the planet; the indirect effect (the particles act as cloud condensation nuclei and thereby change cloud properties) is less certain.

The direct (albedo) effect is generally to cool the planet; the indirect effect (the particles act as cloud condensation nuclei and thereby change cloud properties) is less certain.[SEP]As per Spracklen et al.

As per Spracklen et al.[SEP]the effects are: Aerosol direct effect.

the effects are: Aerosol direct effect.[SEP]Aerosols directly scatter and absorb radiation.

Aerosols directly scatter and absorb radiation.[SEP]The scattering of radiation causes atmospheric cooling, whereas absorption can cause atmospheric warming.

The scattering of radiation causes atmospheric cooling, whereas absorption can cause atmospheric warming.[SEP]Aerosols modify the properties of clouds through a subset of the aerosol population called cloud condensation nuclei.

Aerosols modify the properties of clouds through a subset of the aerosol population called cloud condensation nuclei.[SEP]Increased nuclei concentrations lead to increased cloud droplet number concentrations, which in turn leads to increased cloud albedo, increased light scattering and radiative cooling (first indirect effect), but also leads to reduced precipitation efficiency and increased lifetime of the cloud (second indirect effect).

Increased nuclei concentrations lead to increased cloud droplet number concentrations, which in turn leads to increased cloud albedo, increased light scattering and radiative cooling (first indirect effect), but also leads to reduced precipitation efficiency and increased lifetime of the cloud (second indirect effect).[SEP]In extremely polluted cities like Delhi, aerosol pollutants influence local weather and induce an urban cool island effect during the day.

In extremely polluted cities like Delhi, aerosol pollutants influence local weather and induce an urban cool island effect during the day.[SEP]Black carbon Another albedo-related effect on the climate is from black carbon particles.

Black carbon Another albedo-related effect on the climate is from black carbon particles.[SEP]The size of this effect is difficult to quantify: the Intergovernmental Panel on Climate Change estimates that the global mean radiative forcing for black carbon aerosols from fossil fuels is +0.2 W m−2, with a range +0.1 to +0.4 W m−2.

The size of this effect is difficult to quantify: the Intergovernmental Panel on Climate Change estimates that the global mean radiative forcing for black carbon aerosols from fossil fuels is +0.2 W m−2, with a range +0.1 to +0.4 W m−2.[SEP]Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo.

Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo.[SEP]Human activities Human activities (e.g., deforestation, farming, and urbanization) change the albedo of various areas around the globe.

Human activities Human activities (e.g., deforestation, farming, and urbanization) change the albedo of various areas around the globe.[SEP]However, quantification of this effect on the global scale is difficult, further study is required to determine anthropogenic effects.

However, quantification of this effect on the global scale is difficult, further study is required to determine anthropogenic effects.[SEP]Albedo in Astronomy In astronomy, the term albedo can be defined in several different ways, depending upon the application and the wavelength of electromagnetic radiation involved.

Albedo in Astronomy In astronomy, the term albedo can be defined in several different ways, depending upon the application and the wavelength of electromagnetic radiation involved.[SEP]Optical or Visual Albedo The albedos of planets, satellites and minor planets such as asteroids can be used to infer much about their properties.

Optical or Visual Albedo The albedos of planets, satellites and minor planets such as asteroids can be used to infer much about their properties.[SEP]The study of albedos, their dependence on wavelength, lighting angle ("phase angle"), and variation in time composes a major part of the astronomical field of photometry.

The study of albedos, their dependence on wavelength, lighting angle ("phase angle"), and variation in time composes a major part of the astronomical field of photometry.[SEP]For small and far objects that cannot be resolved by telescopes, much of what we know comes from the study of their albedos.

For small and far objects that cannot be resolved by telescopes, much of what we know comes from the study of their albedos.[SEP]For example, the absolute albedo can indicate the surface ice content of outer Solar System objects, the variation of albedo with phase angle gives information about regolith properties, whereas unusually high radar albedo is indicative of high metal content in asteroids.

For example, the absolute albedo can indicate the surface ice content of outer Solar System objects, the variation of albedo with phase angle gives information about regolith properties, whereas unusually high radar albedo is indicative of high metal content in asteroids.[SEP]Enceladus, a moon of Saturn, has one of the highest known optical albedos of any body in the Solar System, with an albedo of 0.99.

Enceladus, a moon of Saturn, has one of the highest known optical albedos of any body in the Solar System, with an albedo of 0.99.[SEP]Another notable high-albedo body is Eris, with an albedo of 0.96.

Another notable high-albedo body is Eris, with an albedo of 0.96.[SEP]Many small objects in the outer Solar System and asteroid belt have low albedos down to about 0.05.

Many small objects in the outer Solar System and asteroid belt have low albedos down to about 0.05.[SEP]A typical comet nucleus has an albedo of 0.04.

A typical comet nucleus has an albedo of 0.04.[SEP]Such a dark surface is thought to be indicative of a primitive and heavily space weathered surface containing some organic compounds.

Such a dark surface is thought to be indicative of a primitive and heavily space weathered surface containing some organic compounds.[SEP]The overall albedo of the Moon is measured to be around 0.14, but it is strongly directional and non-Lambertian, displaying also a strong opposition effect.

The overall albedo of the Moon is measured to be around 0.14, but it is strongly directional and non-Lambertian, displaying also a strong opposition effect.[SEP]Although such reflectance properties are different from those of any terrestrial terrains, they are typical of the regolith surfaces of airless Solar System bodies.

Although such reflectance properties are different from those of any terrestrial terrains, they are typical of the regolith surfaces of airless Solar System bodies.[SEP]Two common optical albedos that are used in astronomy are the (V-band) geometric albedo (measuring brightness when illumination comes from directly behind the observer) and the Bond albedo (measuring total proportion of electromagnetic energy reflected).

Two common optical albedos that are used in astronomy are the (V-band) geometric albedo (measuring brightness when illumination comes from directly behind the observer) and the Bond albedo (measuring total proportion of electromagnetic energy reflected).[SEP]Their values can differ significantly, which is a common source of confusion.