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How much of a difference would it make if every roof, road and vehicle were painted white? This would certainly reduce the urban heat island effect but how much of a difference would it make to total scattered insolation? Apologies in advance for this the bizarre question.

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Go out into the countryside and look around. Then try to estimate the fraction of Earth's surface that is covered with buildings, roads and vehicles. Hint: it is very small. – dmckee Jun 7 '14 at 18:46
dmckee while this is true in average, enhanced reflectivity in a dense urban area would lower the average absorbed power, and probably the average temperature. But on the other hand, if you are willing to paint all the roofs, why bother? put some solar panels and some solar freakin' roadways: – diffeomorphism Jun 7 '14 at 19:57
up vote 1 down vote accepted

Currently around $3.5 \text{ million }\text{km}^2$ of the earth is under urban population. Source :

Let's assume total area to be painted as white as any other ice sheet would be $2.3 \text{ million }\text{km}^2$

But we already have the following ice sheets, Antarctica ($14 \text{ million }\text{km}^2$), Greenland ($2 \text{ million }\text{km}^2$) and ice sheet's in arctic ocean (average of $7 \text{ million }\text{km}^2$ over the year).

This sums up the total ice mass to be $23 \text{ million }\text{km}^2$

Now these large ice sheets reflect about $2$% of the total sunlight that reaches earth. Even if we do paint every urban building white at maximum it would bring about the reflected sunlight to $2.2$% or let's call it $3$%

But what does this $0.1$ to $1$ percent increase in reflection mean for us?

Currently a total of 70% sunlight is absorbed on earth which is 3,850,000 exajoules per year, if we reduce this to $69% this would mean a reduction of 55,000 exajoules energy absorption per year.

Well, I am by no means an expert but the current absorbed energy keeps the average temperature of earth at $14^\text{o}$, though this process may reduce the average by too less a number to notice, it would definitely mean a lot for the urban areas, as all this reflected energy would bring a targeted cooling effect on the overheated cities!

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Great answer. Thank you. – Seanosapien Jun 11 '14 at 19:31

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