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presented at the 27th Annual Asilomar Microcomputer Workshop
Lots of people talk about global warming, but few offer a solution, and none are cheap. The Kyoto remedy is to reduce the emission of greenhouse gases worldwide by fiat. But stuffing corks into every smokestack and tailpipe will be expensive and politically problematic. In the US alone, cutting CO2 emissions to 80% of the 1990 level may cost $3.6 trillion (1990 dollars), 30 times Apollo’s price tag, and only postpone the inevitable.
On the other hand, damage from unmitigated climate change and social upheavals will surely be vast -- at least $200 trillion over the next century. Rich First Worlders may lose most of the money, but poor Third Worlders below the 10-meter contour will do most of the dying. With globalized culture and CNN showing them every day the life they haven�t got, they are unlikely to passively acquiesce in this fate. Catastrophes may even disrupt developed economies enough to cut off basic resources (e.g. food, arable land, fuel). It is hard to imagine fractious, gridlocked First World institutions coping with such stress without major warfare.
For the same money, why not buy an insurance policy that covers the whole Earth?
The idea of using mirrors in space for propulsion dates back to Tsiolkovsky and Tsander in the 1920s. A conventional rocket boosting continuously would eventually exhaust its fuel, but a mirror generates continuous thrust without fuel, because in space, even insubstantial sunlight exerts pressure. Most treatments have focused on hauling payloads around the solar system. While that form of transportation may eventually happen, the same basic idea can be easily adapted to reduce the amount of sunlight striking the earth (aka "solar constant").
(A real solar sail was launched from a Russian nuclear submarine this year, but reentered after an upper stage failure.)
Space mirrors can also reduce the amount of sunlight striking the earth! To work as a parasol, a sail must hold itself between the Earth and the Sun for many years. The ideal spot is the L1 Lagrange point, 1.5 million kilometers inside Earth’s orbit on the Earth-Sun axis. A parasol will have to actively reconfigure itself to maintain this somewhat unnatural position, but this should be achievable by mid-21st century distributed automation. While providing free thrust to a space mirror, solar photons cannot complete their journey to Earth to heat us up. Intercept enough photons in space, and greenhouse gases become irrelevant!
In fact, the solar sails can be maneuvered to hover over Earth's poles in order to increase solar heating if necessary.
How much shading is enough? Between the mid-16th and 17th centuries, the sunspot cycle shut down, reducing solar output by a mere 0.25%. Astronomers call this “the Maunder minimum”27; historians call it “the Little Ice Age” - the coldest period since the last great ice age 10,000 years ago. The Thames River froze for the first time in recorded history, European population growth stalled, crops failed, and sea ice cut off Iceland from Europe. Tycho Brahe, noted Danish astronomer, recorded winter temperatures 2.7°F below average. We note that the lower limit of IPCC’s estimated Greenhouse temperature change is also 2.7°F, but in the opposite direction. Therefore, manipulating the solar constant by a similar fraction, i.e. creating a “mirrored Maunder Minimum” should let us adjust global temperature just to our liking.
Our calculations indicate a need for 390,000 square kilometers of space mirrors, orbiting at L1, massing hundreds of megatons.
This giant rheostat in the sky has major advantages � it�s:
How could we pay for this scheme? Pre-existing utility premiums and redirected insurance subsidies.
Standard of living is highly correlated with abundant, cheap electricity. 1400 megawatts of solar energy pass through every square kilometer at earth orbit. Any sunlight not reflected for thrust is absorbed and available for use by onboard systems, such as brains and ion engines. If just 10% of this absorbed energy is converted into electricity and beamed to Earth instead, each 10 km2 of sail would displace one major billion-dollar carbon burner (or nuke) on the ground, plus associated pollution. Together the shields could provide total planetary electrical demand by 2050, 300+ quads/year. Replacing the world�s generating plant by 2050 is going to cost roughly $20 trillion; why not set a little aside now for clean energy from space and stay cool too? Displacing terrestrial prime movers that burn carbon somewhere in their cycle may ultimately have a greater beneficial effect on the climate change than shading the sun.
Solar sails can be part of the solution to the problem of global warming and climate change, possibly the whole answer. Intercepting sunlight before it hits earth may also lead to some degree of weather control. Building solar sails requires the development of a massive space infrastructure that does not exist today. Large anomalous reflections may signal Enquiring Minds Out There that they�re not alone. Sunshields in space may not only give humanity a better climate on the ground, but also open the door to the whole solar system, a gift that will keep on giving.
I thank my co-author Ken Roy PE, as well as John Wharton, Eric Hughes, Dwayne A. Day Ph.D., Mike Markowitz, and B. Derk Bruins Ph.D. All mistakes are my responsibility.
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