How much does blacktop contribute to heating the earth?

It is a factor. There’s a phenomenon scientists call the urban heat island effect, and dark pavement is a major contributor.

Yes, a lot, IMO. I live on 5 acres in the hills and while it gets hot, it is nothing compared to the asphalt land of the city. I read somewhere once that the closet big city to me has a record temp. at one one of the shopping malls with about 10 acres of parking lots. It is the hottest part of town.

I believe it!

Blacktop is black because its primary ingredient is bitumen (asphalt), which is… black. I suppose it could be made with coloring agents, but it would take a lot of coloring agent to overcome that black base material, and paint would wear off too soon (and thereby create its own environmental ill effects). All of that would make it pretty expensive, which large users of asphalt are not so keen on paying.

But that’s not “heating the Earth” directly, as it simply reduces albedo, which is a measure of the planet’s reflectiveness. In this case, the Sun still heats the Earth, but reduced albedo helps to hold that heat instead of reflecting it back into space.

Of course, we could fill all of the roads and parking lots with white-roofed (or mirror-roofed) cars. That would help to offset the reduced albedo of the pavement…

@CWOTUS that’s interesting. I have conducted my own personal test of this theory and often the sidewalk feels as hot to my feet as the bitumen. I always assumed it was because the cement sidewalk is not porous whereas most all bitumen is, to varying degrees. I have trod on black earth and red packed and baked earth that was pretty damned hot too, but it didn’t seem as hot as the bitumen. Although an aboriginal friend of mine, one day burned his feet seriously walking on the hot red dirt and his feet were like leather but the temp that day was in the high 30’s and sunny!