Could painting majority of rooftops in the US white help prevent global warming?

although the (in)famous butterfly in the himalaya

could cause an ice-age according to chaos theory,

I am afraid you overestimate the roof effect vastly.

You would think so, but the loss of ice isn't the cause, it is one of the consequences that also accelerates the rate at which the problem progresses.

The problem is due to the fact that some of the sunlight loses enough energy on the trip in through the atmosphere that it doesn't have enough left to get back out if it is reflected back. Certain gases cause this, and increasing thei concentration in the air causes more heat to be trapped. The gases released by certain human activities are added to the gases released by natural processes, so the amount of heat being trapped has increased steadily since industrialization began. Since we can't do much about most of the natural sources, the only way available to avoid Global warming reaching a point where humans can't live is to reduce human production of those types of gases. It would require a large reduction, not a small one, and there is a lot of political opposition related to lost profits by oil and coal companies, and things like that.

The way in which this would help would be to reduce the "urban heat island" effect.

Urban areas are hotter than the surrounding countryside because black tar roofs and concrete don't reduce heat. They gather it and radiate it at night. While white roofs would help to reflect sunlight away from the city, thus lowering the temperature and lowering the need for air conditioning, a better solution would be a massive implementation of green roofing technology. Not only would the urban heat island effect be mitigated, the increased green space would help to clean urban air, help to reduce storm water runoff, as well as absorb carbon dioxide.

No, this wouldn't have a measurable effect on global warming because homes take up such a small percentage of the Earth's surface. It would decrease the effects of urban heat islands on a local scale, but would not have an effect on a global scale.

Yes, it would help a little bit.

To counteract the effects of GW, you'd basically have to paint an entire continent with reflective paint.

Yes, if you believe that CO2 causes global warming. Painting your roof white, will cause your homes attic to be cooler, and will use less energy to keep your house cool in the summer.

This sounded bogus at first but that's an interesting theory. I'm sorry I don't have an answer for that. I bet it would be a good one to post to Popular Mechanics though, they're big into the Green issue.

Nice try, but I think you need to go back to the drawing board, because that's not going to work.

unfortunately, no.