Solar radiation management - AbsoluteAstronomy.com

Solar radiation management (SRM) projects are a type of geoengineering

Geoengineering

The concept of Geoengineering refers to the deliberate large-scale engineering and manipulation of the planetary environment to combat or counteract anthropogenic changes in atmospheric chemistry The Intergovernmental Panel on Climate Change concluded in 2007 that geoengineering options, such...

which seek to reflect sunlight and thus reduce global warming

Global warming

Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

. Examples include the creation of stratospheric sulfur aerosols

Stratospheric sulfur aerosols (geoengineering)

The ability of stratospheric sulfate aerosols to create a global dimming effect has made them a possible candidate for use in geoengineering projects to limit the effect and impact of climate change due to rising levels of greenhouse gases...

. They do not reduce greenhouse gas

Greenhouse gas

A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...

concentrations in the atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

, and thus do not address problems such as ocean acidification

Ocean acidification

Ocean acidification is the name given to the ongoing decrease in the pH and increase in acidity of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide from the atmosphere....

caused by these gases. Their principal advantages as an approach to geoengineering is the speed with which they can be deployed and become fully active, as well as their low financial cost. By comparison, other geoengineering techniques based on greenhouse gas remediation

Greenhouse gas remediation

Greenhouse gas remediation projects are a type of geoengineering and seek to remove greenhouse gases from the atmosphere, and thus tackle the root cause of global warming. These techniques either directly remove greenhouse gases, or alternatively seek to influence natural processes to remove...

, such as ocean iron fertilization

Iron fertilization

Iron fertilization is the intentional introduction of iron to the upper ocean to stimulate a phytoplankton bloom. This is intended to enhance biological productivity, which can benefit the marine food chain and remove carbon dioxide from the atmosphere. Iron is a trace element necessary for...

, need to sequester the anthropogenic carbon excess before they can arrest global warming

Global warming

. Solar radiation management projects can therefore be used as a geoengineering

Geoengineering

'quick fix' while levels of greenhouse gases can be brought under control by greenhouse gas remediation

Greenhouse gas remediation

techniques.

A study by Lenton and Vaughan suggest that marine cloud brightening and stratospheric sulfur aerosols

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 particles consist of a mixture of sulfuric acid...

are each capable of reversing the warming effect of a doubling of the level of

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

in the atmosphere

Atmosphere

(when compared to pre-industrial levels).

Background

The phenomenon of global dimming

Global dimming

Global dimming is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4%...

is widely known, and is not necessarily a geoengineering technique. It occurs in normal conditions, due to aerosols caused by pollution

Pollution

Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

, or caused naturally as a result of volcanoes and major forest fires. However, its deliberate manipulation is a tool of the geoengineer. The majority of recent global dimming

Global dimming

has been in the troposphere

Troposphere

The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

, except that resulting from volcano

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

s, which affect mainly the stratosphere

Stratosphere

The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...

.

By intentionally changing the Earth's albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

, or reflectivity, scientists propose that we could reflect more heat back out into space, or intercept sunlight before it reaches the Earth through a literal shade built in space. A 0.5% albedo increase would roughly halve the effect of CO₂ doubling.

These geoengineering

Geoengineering

projects have been proposed in order to reduce global warming

Global warming

. The effect of rising greenhouse gas

Greenhouse gas

concentrations in the atmosphere

Atmosphere

on global climate is a warming effect on the planet. By modifying the albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

(whiteness) of the Earth's surface, or by preventing sunlight reaching the Earth by using a solar shade, this warming effect can be cancelled out - although it should be noted that the cancellation is imperfect, with regional discrepancies remaining.

The applicability of many techniques listed here has not been comprehensively tested. Even if the effects in computer simulation models or of small-scale interventions are known, there may be cumulative problems such as ozone depletion

Ozone depletion

Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...

, which only become apparent from large scale experiments.

Various small-scale experiments have been carried out on techniques such as cloud seeding

Cloud seeding

Cloud seeding, a form of intentional weather modification, is the attempt 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 processes within the cloud...

, increasing the volume of stratospheric sulfur aerosols

Stratospheric sulfur aerosols

and implementing cool roof

Cool roof

Cool roofs are the roofs that can deliver high solar reflectance and high thermal emittance...

technology.

As early as 1974, Russian expert Mikhail Budyko suggested that if global warming became a problem, we could cool down the planet by burning sulfur in the stratosphere, which would create a haze. Paul Crutzen suggests that this would cost 25 to 50 billion dollars per year. It would, however, increase the environmental problem of acid rain

Acid rain

Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions . It can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of carbon dioxide, sulfur dioxide and nitrogen...

. However, this is now believed to be a minor side effect.

A preliminary study by Edward Teller and others in 1997 presented the pros and cons of various relatively "low-tech" proposals to mitigate global warming through scattering/reflecting sunlight away from the Earth via insertion of various materials in the upper stratosphere, low earth orbit, and locations.

Limitations

As well as the imperfect cancellation of the effect of greenhouse gases on global warming

Global warming

, there are other significant problems with solar radiation management as a from of geoengineering

Geoengineering

not least of these are effects on the global hydrological cycle and the inability of such techniques to reduce ocean acidification

Ocean acidification

Ocean acidification is the name given to the ongoing decrease in the pH and increase in acidity of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide from the atmosphere....

.

Particular to solar radiation management, a risk of abrupt cessation exists. If SRM were to abruptly stop, the climate would rapidly warm. This would cause a sudden rise in global temperatures towards levels which would have existed without the use of the geoengineering technique. The rapid rise in temperature may lead to more severe consequences than a gradual rise of the same magnitude.

Atmospheric projects

These projects seek to modify the atmosphere, either by enhancing natural processes such as the sulfur cycle

Sulfur cycle

The sulfur cycle are the collection of processes by which sulfur moves to and from minerals and living systems. Such biogeochemical cycles are important in geology because they affect many minerals...

, or by using artificial techniques such as reflective balloons.

Stratospheric sulfur aerosols

Stratospheric sulfur aerosols (geoengineering)

: proposed by Paul Crutzen, with the purpose to modify the Earth's albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

with reflective or absorptive materials spread over portions of its surface. This would typically be achieved using hydrogen sulfide

Hydrogen sulfide

Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

or sulfur dioxide

Sulfur dioxide

Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

, delivered using artillery

Artillery

Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

, aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

(such as the high-flying F15-C) or balloons.
Ozone depletion

Ozone depletion

is a risk of such techniques, but only if high enough quantities of aerosols drift to, or are deposited in, polar stratospheric clouds before the levels of CFCs and other ozone destroying gases fall naturally to safe levels because CFCs can settle on larger sulfate particles, increasing their ozone destroying potential.
This proposal, not unlike the others, carries with it considerable risks, including increased drought or acid rain.
Broadly speaking, this technique is seen as a credible geoengineering scheme, although not one without major risks, and challenges for its implementation. This technique can give >3.7W/m² of globally averaged negative forcing, which is sufficient to entirely offset the warming caused by a doubling of CO₂.

Reflective aerosols or dust

Methods based on increasing the aerosol content in the lower stratosphere for climate modification were proposed by a Russian scientist, Budyko.

United States Patent 5003186 suggested that tiny metal flakes could be "added to the fuel of jet airliners, so that the particles would be emitted from the jet engine exhaust while the airliner was at its cruising altitude." Alternative proposals, not known to have been published in peer-reviewed journals, include the addition of silicon compounds to jet fuel to make silicon dioxide

Silicon dioxide

The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

particles in the exhaust.

A more sophisticated approach, using multi-layered nanoparticles (consisting of aluminum and barium titanate

Barium titanate

Barium titanate is the inorganic compound with the chemical formula BaTiO3. Barium titanate is a white powder and transparent as larger crystals...

), was published by David Keith

David Keith (scientist)

David W. Keith is a Canadian environmental scientist. He is the former director of the Institute for Sustainable Energy, Environment and Economy Energy and Environmental Systems Group at the University of Calgary. Keith is noted for his work in carbon dioxide air capture, and has been featured on...

in 2010. He suggests utilizing the effects of photophoresis

Photophoresis

Photophoresis denotes the phenomenon that small particles suspended in gas or liquids start to migrate when illuminated by a sufficiently intense beam of light. The existence of this phenomenon is owed to a non-uniform distribution of temperature of an illuminated particle in a fluid medium...

to increase the amount of time the aerosols stay airborne.

Alleged secret experiments with aircraft exhaust modification are one version of the Chemtrail conspiracy theory.

In 1992, a report by the US National Academy of Sciences (NAS) on geoengineering noted that dust is a better choice compared to sulphur, because dust is from natural soil and so should have no noticeable effect on the ground as it gradually falls into the troposphere and rains out. It estimated that about 10¹⁰ kg dust would be required to mitigate the warming from a doubling of atmospheric or about 1 kg dust per 100 t of carbon emissions.

An example of the effects of the imposition of aerosol particles in the atmosphere can be found in history. Comets have been blamed for the dramatic but brief cooling period which commenced in 1159 BCE, and resulted in widespread disruption to civilisations at the time. However, this mechanism, and even the involvement of a comet

Comet

A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

, is not universally accepted. If a comet was indeed to blame, the action of its aerosols could also have been by the mechanism of cloud condensation nuclei

Cloud condensation nuclei

Cloud condensation nuclei or CCNs are small particles typically 0.2 µm, or 1/100 th the size of a cloud droplet ) about which cloud droplets coalesce. Water requires a non-gaseous surface to make the transition from a vapour to a liquid. In the atmosphere, this surface presents itself as tiny...

. Other examples of climate change events linked to comets include the famines around 536 CE.

Cloud whitening / marine cloud brightening / cloud reflectivity enhancement

Various schemes have been suggested,
such as that proposed by John Latham

John Latham

John Latham may refer to:* John Latham , British physician, naturalist and author* John Latham English physician, President of the Royal College of Physicians...

and Stephen Salter

Stephen Salter

Stephen Hugh Salter is Emeritus Professor of Engineering Design at the University of Edinburgh and inventor of the eponymous Salter duck wave energy device...

, which works by spraying seawater in the atmosphere to increase the reflectiveness of clouds. The extra condensation nuclei created by the spray will change the size distribution of the drops in existing clouds to make them whiter. The sprayers would use fleets of unmanned Rotor ships known as Flettner vessels to spray mist created from seawater into the air to thicken clouds and thus reflect more radiation from the Earth. The whitening effect is created by using very small cloud condensation nuclei

Cloud condensation nuclei

, which whiten the clouds due to the Twomey effect

Twomey effect

Twomey effect — describes how cloud condensation nuclei , possibly from anthropogenic pollution, may increase the amount of solar radiation reflected by clouds. This is an indirect effect....

.

This technique can give >3.7W/m² of globally averaged negative forcing,
which is sufficient to reverse the warming effect of a doubling of CO₂.

Ocean sulfur cycle enhancement

Enhancing the natural sulfur cycle

Sulfur cycle

in the Southern Ocean

Southern Ocean

The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...

ocean by fertilizing a small portion with iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

in order to enhance dimethyl sulfide

Dimethyl sulfide

Dimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...

production and cloud reflectivity

Reflectivity

In optics and photometry, reflectivity is the fraction of incident radiation reflected by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength...

. The goal is to slow Antarctic

Antarctic

The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...

ice from melting and raising sea level

Sea level

Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

. Such techniques also tend to sequester carbon, but in this specific project the enhancement of cloud albedo was both the desired outcome and measured result. An alternative technique proposes the vertical mixing of ocean water, to bring deep-water nutrients to surface plankton. This technique can give only 0.016W/m² of globally averaged negative forcing, which is essentially insignificant for geoengineering

Geoengineering

purposes.

Reflective balloons

Placing billions of aluminized, hydrogen-filled balloons in the stratosphere has been suggested to provide a reflective screen.

These reflectors would be placed at a high enough altitude so that they do not interfere with air traffic. The cost estimate is about 20 times as much as the distribution of dust in the stratosphere, making these schemes economically nonviable. The large number of reflectors and the trash problem posed by their fall make the system unattractive.

Cloud seeding

has been proposed using various methods to to distribute the cloud-seeding materials, including airliners and ships or power plants. Reck (1978) studied the effect of increases in cloud cover and, using a radiative-convective atmospheric model, found that a 4 to 5 percent increase in low-level cloud cover would be sufficient to offset the warming predicted from a doubling of preindustrial CO₂. This value is in reasonable agreement with Randall et al. (1984), who estimated that a 4 percent increase was required in the amount of marine stratocumulus, which comprises the bulk of the low clouds on a global basis."

Cool roof

Painting pavements and roof materials in white or pale colours to reflect solar radiation, known as 'cool roof

Cool roof

Cool roofs are the roofs that can deliver high solar reflectance and high thermal emittance...

' technology, and encouraged by legislation in some areas (notably California). This is a benign technique, although limited in its ultimate effectiveness by the costrained surface area available for treatment. This technique can give between 0.01-0.19W/m² of globally averaged negative forcing, depending on whether cities or all settlements are so treated. This is generally insignificant when compared to the 3.7W/m² of positive forcing from a doubling of CO₂. However, in many cases it can be achieved at little or no cost by simply selecting different materials. Further, it can reduce the need for air conditioning

Air conditioning

An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

, which causes CO₂ emissions which worsen global warming

Global warming

. For this reason alone it is still demonstrably worth pursuing.

Reflective sheeting

Reflective plastic sheets covering 67000 square miles (173,529.2 km²) of desert, to reflect the Sun’s energy. This technique can give globally averaged 1.74W/m² of negative forcing, which is insufficient to offset the 3.7W/m² of positive forcing from a doubling of CO₂, but is still a very significant contribution and is sufficient to offset the current level of warming (approx. 1.7W/m²). However, the effect would be strongly regional, and would not be ideal for controlling Arctic shrinkage

Arctic shrinkage

Ongoing changes in the climate of the Arctic include rising temperatures, loss of sea ice, and melting of the Greenland ice sheet. Projections of sea ice loss suggest that the Arctic ocean will likely be free of summer sea ice sometime between 2060 and 2080, while another estimate puts this date at...

, which is one of the most significant problems resulting from global warming.

Ocean changes

An early geoengineering

Geoengineering

idea was to use pale coloured floating litter

Litter

Litter consists of waste products such as containers, papers, wrappers or faeces which have been disposed of without consent. Litter can also be used as a verb...

within certain stable oceanic gyres. This litter would tend to group into large and stable areas, such as the Great Pacific Garbage Patch

Great Pacific Garbage Patch

The Great Pacific Garbage Patch, also described as the Pacific Trash Vortex, is a gyre of marine litter in the central North Pacific Ocean located roughly between 135°W to 155°W and 35°N to 42°N...

.

Oceanic foams have also been suggested, using microscopic bubbles suspended in the upper layers of the photic zone

Photic zone

The photic zone or euphotic zone is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur...

Forestry

Reforestation

Reforestation is the natural or intentional restocking of existing forests and woodlands that have been depleted, usually through deforestation....

in tropical areas has a cooling effect. Deforestation

Deforestation

Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....

of high-latitude

Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

and high-altitude

Altitude

Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

forests exposes snow

Snow

Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...

and this increases albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

Grassland management

Changes to grassland have been proposed to increase albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

. This technique can give 0.64W/m² of globally averaged negative forcing, which is insufficient to offset the 3.7W/m² of positive forcing from a doubling of CO₂, but could make a minor contribution towards it.

High-albedo crop varieties

Selecting or genetically modifying

Genetically modified organism

A genetically modified organism or genetically engineered organism is an organism whose genetic material has been altered using genetic engineering techniques. These techniques, generally known as recombinant DNA technology, use DNA molecules from different sources, which are combined into one...

commercial crops with high albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

has been suggested. This has the advantage of being relatively simple to implement, with farmers simply switching from one variety to another. Temperate

Temperate

In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...

areas may experience a 1°C cooling as a result of this technique. This technique is an example of bio-geoengineering

Bio-geoengineering

Bio-geoengineering is a form of geoengineering which seeks to use or modify plants or other living things to modify the Earth's climate.Bio-energy with carbon storage, afforestation projects, and ocean nourishment could be considered examples of bio-geoengineering....

. This technique can give 0.44W/m² of globally averaged negative forcing, which is insufficient to offset the 3.7W/m² of positive forcing from a doubling of CO₂, but could make a minor contribution towards it.

Space projects

Space-based geoengineering

Geoengineering

projects are seen by many commentators and scientists as being far-fetched at present.

Space mirrors

Mirrors in space: proposed by Roger Angel with the purpose to deflect a percentage of solar sunlight into space, using mirrors orbit

Orbit

In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

ing around the Earth.

Moon dust

Mining moon dust to create a shielding cloud was proposed by Curtis Struck at Iowa State University

Iowa State University

Iowa State University of Science and Technology, more commonly known as Iowa State University , is a public land-grant and space-grant research university located in Ames, Iowa, United States. Iowa State has produced astronauts, scientists, and Nobel and Pulitzer Prize winners, along with a host of...

in Ames

Ames, Iowa

Ames is a city located in the central part of the U.S. state of Iowa in Story County, and approximately north of Des Moines. The U.S. Census Bureau designates that Ames, Iowa metropolitan statistical area as encompassing all of Story County, and which, when combined with the Boone, Iowa...

Dispersive solutions

Several authors have proposed dispersing light before it reaches the Earth by putting a very large diffraction grating

Diffraction grating

In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...

(thin wire mesh) or lens

Lens (optics)

A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...

in space, perhaps at the L1 point between the Earth and the Sun. Using a Fresnel lens in this manner was proposed in 1989 by J. T. Early. Using a diffraction grating was proposed in 1997 by Edward Teller

Edward Teller

Edward Teller was a Hungarian-American theoretical physicist, known colloquially as "the father of the hydrogen bomb," even though he did not care for the title. Teller made numerous contributions to nuclear and molecular physics, spectroscopy , and surface physics...

, Lowell Wood

Lowell Wood

Lowell Wood is an American astrophysicist who has been involved with the Strategic Defense Initiative and with geoengineering studies. He has been affiliated with Lawrence Livermore National Laboratory and the Hoover Institution, and chaired the EMP Commission. Wood invented the Mosquito laser.-...

, and Roderick Hyde. In 2004, physicist and science fiction author Gregory Benford

Gregory Benford

Gregory Benford is an American science fiction author and astrophysicist who is on the faculty of the Department of Physics and Astronomy at the University of California, Irvine...

calculated that a concave rotating Fresnel lens

Fresnel lens

A Fresnel lens is a type of lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design...

1000 kilometres across, yet only a few millimeters thick, floating in space at the point, would reduce the solar energy reaching the Earth by approximately 0.5% to 1%. He estimated that this would cost around US$

United States dollar

The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....

10 billion

1000000000 (number)

1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109....

up front, and another $10 billion in supportive cost during its lifespan. These ideas conflict with reality poorly in that a 1000 kilometre diameter fresnell is a 1000 kilometre diameter solar sail and it would cost a stupendous amount of energy to hold such a mirror at Lagrange-1 with the solar wind blowing at gale force way out there. Side-effects include that, if this lens were built and global warming were avoided, there would be less incentive to reduce greenhouse gases, and humans might continue to produce too much carbon dioxide until it caused some other environmental catastrophe, such as a chemical change in ocean water

Ocean acidification

Ocean acidification is the name given to the ongoing decrease in the pH and increase in acidity of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide from the atmosphere....

that could be disastrous to ocean life

Marine biology

Marine biology is the scientific study of organisms in the ocean or other marine or brackish bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather...

Background

Limitations

Atmospheric projects

Stratospheric sulfur aerosols

Reflective aerosols or dust

Cloud whitening / marine cloud brightening / cloud reflectivity enhancement

Ocean sulfur cycle enhancement

Reflective balloons

Cloud seeding

Cool roof

Reflective sheeting

Ocean changes

Forestry

Grassland management

High-albedo crop varieties

Space projects

Space mirrors

Moon dust

Dispersive solutions

See also

Further reading