Solar Radiation Management - Background

Background

The phenomenon of global dimming is widely known, and is not necessarily a geoengineering technique. It occurs in normal conditions, due to aerosols caused by pollution, 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 has been in the troposphere, except that resulting from volcanos, which affect mainly the stratosphere.

By intentionally changing the Earth's albedo, 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 projects have been proposed in order to reduce global warming. The effect of rising greenhouse gas concentrations in the atmosphere on global climate is a warming effect on the planet. By modifying the albedo (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 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, which only become apparent from large scale experiments.

Various small-scale experiments have been carried out on techniques such as cloud seeding, increasing the volume of stratospheric sulfur aerosols and implementing cool roof 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. 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 L₁ locations.