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No. 48 - June 2005

Cooling the Earth

Global warming is one of the most serious problems facing the world today. Certainly the Prime Minister thinks so and the Archbishop of Canterbury fears for the future of the human race. Despite claims that the recent warming is natural, the consensus among climatologists is that the world-wide burning of fossil fuels is largely to blame - increasing emissions of carbon dioxide (CO2), a major greenhouse gas. An unpleasant climatic change is coming with various dire consequences. Overall, mankind is conducting a dangerous experiment with the world's climate, the damage from which could end up costing at least £130 trillion over the next century.

Will the Kyoto Protocol ameliorate the problem? It seems very unlikely. Considering that climatologists are calling for an immediate cut in CO2 output of 60 per cent, it is too little and too late. Instead of falling, CO2 emissions are still rising; since Kyoto in 1997, global traded energy use has risen by 10 per cent and the use of fossil fuels by 10.5 per cent. Moreover, the country that produces the most greenhouse gases (USA) refuses to participate because of the cost. However, even if CO2 levels are slashed in the 21st century and the level stabilises at between 450 and 1000 ppm, the temperature will continue to rise for centuries and sea level will continue to rise for millennia (1).

What then can be done to avoid catastrophe? Is there a high-tech fix? Technology caused the problem; can technology solve it?

Ignoring proposals that merely slow the increase in the output of greenhouse gases, such as switching all electricity generation to nuclear power and/or renewable energy, the technical fixes fall into two groups: those that try to deal with the increasing CO2 and those that attempt to cool the Earth. The former include dumping iron filings in the oceans, growing mutant algae in the high seas or attempting to sequestrate all the CO2 produced by burning fossil fuels, perhaps by burying it in depleted oil fields. The latter include injecting sub-micrometer dust into the stratosphere in shells fired by naval guns, increasing cloud cover by seeding and painting every roof and road white!

An increase in the amount of carbon dioxide is not in itself harmful, except in acidifying the oceans and so harming some sea creatures. Indeed, it could result in an increase in food production as plants absorb more CO2. What we want to avoid is the consequent rise in temperature; this is what the second group of proposals attempts to address. Because CO2 contributes only about 70 % of the global warming effect of man-made greenhouse gases, assessments of warming based only on CO2 rather underestimate it. What is needed is a way of cooling the Earth, regardless of the effects of atmospheric gases.

One way to lower the temperature of the Earth would be to reduce the amount of solar energy reaching it. This could be achieved by placing a shield between the Earth and the Sun so that less solar energy reaches the planet. One geophysicist called this idea 'wild and wacky', although he had no better solution (2).

The idea of placing mirrors in space dates back to Tsiolkovsky and Tsander in the 1920s. That was for propulsion (solar sails), but such a mirror can also reduce the amount of sunlight striking Earth. To work as a solar shield, the mirror must hold itself between the Earth and the Sun for many years. The obvious place for this is at the Earth/Sun L1 Lagrangian point. This is the point between the Earth and the Sun, about 1.5 million km from Earth, where the gravity from the Sun is balanced by that from Earth. Already several artificial satellites have made use of it and the Solar and Heliospheric Observatory Satellite (SOHO) is there now. Because L1 is unstable, the mirror would have to be provided with the means to maintain its position.

Perhaps the first person to suggest using such a shield for this purpose was James Early of the Lawrence Livermore National Laboratory (LLNL) in the USA (3). He proposed a glass shield made from Moon rock that would be launched by mass driver from a manufacturing plant on the Moon. His shield would be 2000 km in diameter and about 10 μm thick, either opaque or transparent in the form of a Fresnel lens, the latter refracting light away from the Earth. In either case, the shield would reduce insolation by about 2 per cent, offsetting the predicted greenhouse trapping expected during this century (based on a doubling of the level of CO2). The shield would weigh about 100 Mt and cost from $1-10 trillion. However, Early pointed out that the economic impact of global warming might be much greater than this. Indeed, it has been estimated that damage from unmitigated climate change over the next century could cost at least $200 trillion and that cutting emissions to 80 per cent of the 1990 level in the US alone may cost $3.6 trillion, thirty times the cost of the Apollo space missions (4).

About the same time as Early's proposal was published, a letter outlining almost the same idea was published by a Swiss scientist (5). His mirror would be made of aluminium, weighing at least 45 Mt. To compensate for a temperature increase on Earth of 2.5 degrees K, the mirror would need to reduce solar radiation by 3.5 per cent and be about 4.5 million square kilometres in area (or a disc 2393 km in diameter).

Kenneth Roy and Robert Kennedy (4) have also advocated shielding at the Earth/Sun L1, but with a shield only 618 km in diameter. They calculated that this would reduce insolation by 0.25 per cent, resulting in a drop in temperature of 1.5 degrees K, the reduction allegedly experienced during 'the Little Ice Age', the period between the mid-sixteenth and seventeenth centuries when there was an absence of sunspots (the Maunder Minimum). Coincidentally, 1.5 degrees K is the lower limit of the IPCC's estimated increase. Roy suggested that, apart from cooling Earth, the shield could generate electricity that could be beamed to Earth by microwave, so paying for the shield. Because each square kilometre of shield would receive 1.4 GW, even if only 10 per cent of that energy were converted, this would provide the total projected planetary electrical demand for 2050 (9.5 TW), incidentally displacing the burning of fossil fuels for this purpose.

Roy and Kennedy also pointed out that the deployment of such a shield would encourage development of the Solar System, something that we need to do anyway. We need to establish extra-terrestrial colonies, not because the Earth's climate will become uncomfortable, but because there are several major threats to the continuation of civilization on Earth (2). Space exploration has already proved its value in communications and monitoring the Earth's environment. It might provide the only realistic means of bringing global warming under control.

What notice has been taken of this idea? Five years ago, New Scientist carried an article that reviewed Early's work (6). It also commented on that of two other scientists at the LLNL, who modelled the effect of such a shield, believing that this would show that the idea would not work (7). To their surprise, the model showed that it would. The New Scientist article also noted the interest in this matter by Edward Teller and others (8, 9). Teller founded the LLNL. In the USA, there is no funding or apparent interest in actually solving global warming; all the current work is centred on understanding the problem in more detail.

The idea of using a shield to cool the Earth came to Early after seeing the ideas of Fogg (10) and Freitas (11) who proposed such a method to help cool Venus as part of terraforming.

Steuart Campbell


  1. 'Kyoto won't stop climate change', New Scientist, 9 October 2004
  2. Bill McGuire: A Guide to the End of the World, OUP 2002
  3. James T Early: 'Space-Based Solar Shield to Offset Greenhouse Effect', J. Brit. Interplanetary Soc., 42, pp 567-69 (1989)
  4. Kenneth I. Roy and Robert Kennedy: 'Mirrors and Smoke - Ameliorating Climate Change with Giant Solar Sails', Whole Earth Review, Summer 2001
  5. Walter Seifritz: 'Mirrors to halt global warming', Nature, 340, 24 August 1989
  6. Nicola Jones: 'Sunblock', New Scientist, 23 September 2000
  7. Bala Govindasamy and Ken Caldeira: 'Geoengineering Earth's radiation balance to mitigate CO2-induced climate change', Geophysical Research Letters, 27/14, pp. 2141-4, 15 July 2000
  8. Edward Teller and Roderick Hyde: 'Global warming and ice ages: 1. Prospects for physics-based modulation of global change', a paper submitted to the 22nd International Seminar on Planetary Emergencies, Erice (Sicily), 20-23 August 1997, preprint UCRL-JC128715 by the LLNL
  9. Edward Teller, Roderick Hyde and Lowell Wood: 'Active climate stabilization: practical physics-based approaches to prevention of climate change', an article submitted to the National Academy of Engineering Symposium in Washington DC, 23-4 April 2002, preprint UCRL-JC-148012 by LLNL
  10. M J Fogg: 'The terraforming of Venus', J. Brit. Interplanetary Soc. 40, pp. 551-64 (1987)
  11. Robert A Freitas Jr: 'Terraforming Mars and Venus using machine self-replicating systems (SRS)', J. Brit. Interplanetary Soc. 36, pp. 139-42 (1983)


Cover page

From the President

Cooling the Earth

See the Sun in a different light

The 2005 Scottish Astronomy Weekend

Z Ursae Maioris

The Televue Radian eyepiece

The Society at work and the City Observatory

About the ASE Journal

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