How much of the planet would we have to cover with mirrors to neutralize the greenhouse effect?

Answer 1

How much of your brain would we have to cover with intelligence to neutralize the idiot effect?

Answer 2

Hey, NASA is looking for you, or your ideas. They are currently looking into what would it take to put up and unfurl a bunch of mirrors between the earth and the sun.
The loud laughter coming from the building is not promising.
But, in principle, it would work and is a good idea; expensive but a good idea. If nothing else works, this would.
Consider this, if the mirror was far enough from the earth, it wouldn't need to be "that" big to cover 10% of the earth, and lower global warming and heating by 10%, day and night, all over the globe. Not as crazy as might seem at first thought.

A more difficult problem is where to put it so the shadow falls on the earth? Check with your orbital mechanics book you left outside. Don't forget about solar wind pressure that can be used instead of propellant.
At one time, NASA considered sending satellites to the far planets using "Solar Sail". Check it out in the Internet.

Answer 3

First of all although your question is valid, your imaginary planet, I would venture to say is very much imaginary. Regional concentrations of gases are known to exist however, and the Great Red Spot on Jupiter is a primary example. The implication from your question is that all greenhouse gas is CO2. This is not true. There are many other greenhouse gases CH4 is a primary example. Some greenhouse gases are stronger than others meaning that for the same amount of gas the heating effect is larger. Since stronger greenhouse gases do exist, and you have conditioned your question on the equality of the mass, a greenhouse gas that is stronger than CO2 for the same amount of molecules, will produce great heating effect if the strength of the other greenhouse gas is greater than the ratio of a mole of the specified other greenhouse/ the mole of CO2, there would be a heating effect greater than that produced by the same mass of CO2, if the ratio of the respective moles exceeds the inverse. Given the same mass of CO2 a gas with twice the molecular weight of CO2 would contain one half as many molecules. The heating effect to be greater than that of CO2 would have to be greater than 2.

Answer 4

The radiative forcing is 0.6 to 2.4 W/m^2 with a most probable value of 1.6 W/m^2. The average solar constant is 1366 W/m^2 over the earth's cross section of 127,400,000 km^2. The reflectivity of a cheap Al mirror is about 90% and the average albedo of the Earth is 0.3. The required area is thus 1.6 W/m^2/1366W/m^2*127,400,000km^2/(.9-.3) =249,000 km^2
Note that this result applies at the equator. Elsewhere divide by cos(latitude) to get the correct result.

Although the number looks large, it is within human capabilities to do this. The total area is equivalent to approximately 14 New Yorks. Humans have built more than 14 large cities. That being said, there are better options.

Answer 5

Just to clear up some misconceptions above---mirrors on the ground would work. In the greenhouse effect, visible light from the Sun is absorbed at or near ground level. Some of this energy is then re-radiated upwards at far-infrared wavelengths. If the atmosphere is opaque at those wavelengths (because of greenhouse gasses), then the heat is retained by the Earth instead of radiating into space.

If you put a mirror on the ground, the visible light from the Sun is reflected back into space instead of being absorbed. Since the greenhouse gasses (aside from water vapor droplets) are transparent to visible light, that energy will be re-radiated into space, reducing the heating of the Earth.

Answer 6

Beleive it or not this has been considered - both using mirrors on Earth and placing them in space.

There are problems locating them on Earth - the planet revolves and is in darkness half the time, when it's daylight it can be cloudy, although daylight in morning and evening the sun is low on the horizon (the mirrors would be most effective at 1pm when the sun is at it's highest point. Because of these factors the efficiency of the mirrors is likely to be about 20 to 25% of the maximum.

Add in that the atmosphere difuses sunlight, more solar radiation can be reflected from space than from Earth, if they're wet following rain the sunlight will be refracted in all directions, to be effective they would need to track the sun's progress through the sky and this would require huge amounts of power to drive the massive machinery needed. The efficiency is now reduced to perhaps 15%.

The above answer is an excellent one and I'm sure the math is correct but I fear night-time, cloud etc may have been overlooked. Perhaps an area of 1.5 million square km would be more appropriate.

The scientists who researched the space mirrors idea came up with a figure of 100,000 square km. This is a huge object to construct in space, one advantage of being in space is that there's no weather and if it's constructed at the L1 point there's no gravity either (this is the point 1.5 million miles from Earth where the sun's gravity balances that of Earth).

The mirror could be exceptionally lightweight, a similar scheme to construct a sunshade in space would use large glass discs each weighing just 1 gramme and complete with onborad computer and solar powered solar-sails to point the discs toward the sun.

At 1 gramme a piece a rocket designed to carry a heavy payload could carry perhaps 100 million 'mirror panels' at a time (the Shuttle could carry 23 million). 100 rockets, 100 million panels a time, 10 sqaure metres per panel and you have your 100,000 square km solar mirror.

More info...
http://www.nytimes.com/2006/06/27/science/earth/27cool.html?ex=1309060800&en=d0d351a5cf6b48d1&ei=5088&partner=rssnyt&emc=rss
http://news.bbc.co.uk/1/shared/spl/hi/picture_gallery/07/programmes_global_sunshade/html/1.stm

Answer 7

This would do nothing. Mirrors would have to be placed into orbit, outside of the atmosphere. The cost of doing this would be much, MUCH more than the cost of preventative measures.

Edit: While mirrors would reduce a localized warming effect such as the urban heat island phenomenon, the more practical way to do this would be to change black roofs to white, or utilize green roofing. However, while local temperatures would lower and AC costs would be less, the overall problem with global warming is that heat energy cannot escape the layer of green house gasses surrounding the planet.

There are cheaper and more practical ways to make positive changes for the environment.

Answer 8

Too much. It would be more cost effective to create a solar umbrella in space than to build land based solar arrays to neutralize the greenhouse effect.

Answer 9

You know I always wondered it all the rooftops and roads were white instead of black the world wouldn't be a cooler place. It seems asphalt holds more heat than CO2. I mean it's 80 here during the day and at night it goes down in the 40's. That's pretty rapid heat dissapation but the road stays warm most of the night.

Joe cool and idiot girl seem to be very quick to shoot down your idea. I think they must be very closed mided. They don't know that it wouldn't work. I think you're onto something.

Maybe that's what we could use the vast deserts for, No can live there or grow anything anyway. And the lawmakers have just about kicked us off-roader out for good already.

Answer 10

According to the DEFINITION of the greenhouse effect it would do nothing. The sunlight has already lost enough of it's energy that it can't make it back out through the atmosphere into space when it's reflected. You could reflect 100% of the sunlight, and have no effect at all.

Answer 11

Actually to all you nay Sayers, that question is not that far fetched. It is widely believed that the vapour trails being left by jet planes is laced with aluminium oxide. The purpose being to slow down global warming. Its done on the sly because the U.S. does not like to admit to global warming and also the health concerns of dumping aluminium oxide into the atmosphere. Water samples taken from areas with jet streams in the air shows 9 times the normal rate.