Asphalt Pavement - Black Surfaces and Sunlight

Environmental Effects of Asphalt Pavements, Roofs, and Parking Lots

  • There are over 100,000 square miles of black asphalt pavement and roofs in the USA.

  • The fact that all such areas have a black color causes massive amounts of solar energy to immediately get absorbed, warming the environment. Walking barefoot across an asphalt parking lot on a bright summer day confirms that fact.

  • If those huge areas could be made white instead of black, they could immediately REFLECT a lot of sunlight back out to space rather than absorbing it.

  • This relatively minor change could help combat Global Warming.

This presentation was first placed on the Internet in August 2007.

This presentation is meant as an EXAMPLE of the sort of thinking that may be necessary to overcome Global Warming problems that humanity is beginning to face and will face for apparently at least 140 more years in the near future.

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We note that our investigation of the scientific analysis of global warming included calculations regarding each of the many variables that can affect global warming. At the end of this presentation are a number of links, the first of which contains those calculations. It might be possible that a credible solution to our dreadful situation might come from affecting any one of those variables. As an example of this logic, this example is provided here:

The Earth's albedo (reflectance) to the Sun's energy is around 34% as indicated in the first presentation. Whether or not the atmosphere acts as a blanket, the Earth would have a harder time becoming dangerously hot if less of the Sun's energy were absorbed by the Earth. Imagine if there were some way that we might somehow increase that albedo a little, maybe up to 36%. The effect (as calculable by the equations in the first presentation) would be a net reduction of incoming energy from 66% to 64%, a significant amount of energy (around 4 * 1015 watts, around 8,000 times as much energy as ALL the electricity used in the United States!). That much change would result in a reduction of the Earth's equilibrium temperature by around 3.9°F., as can be confirmed with the equations of the first page of this presentation.

Could something like this be done? It is not clear whether human activities would be capable of making such a change. That amount of change might not be enough to really eliminate all the problems, but it might enable the persistent existence of plants and animals and people on Earth.

The most logical possibility that occurred to me is regarding the fact that our Government says there are around 8.5 million miles of roads in the US, with the majority of them being paved with asphalt. There are also an impressive amount of area of parking lots which are all asphalt, particularly in and near cities, as well as a surprisingly large number of flat-roofed buildings that have asphalt-based roofs.

This all indicates that there are well over 100,000 square miles of area of the United States that is currently covered by Asphalt, in pavement in highways and roads, in pavement in parking lots, in the Asphalt roofing on countless flat-roofed buildings, etc. (The entire country has around 36 times that area.) Asphalt happens to be black and it has an extremely high absorbtivity and emissivity of solar energy, generally described as being around 0.95 or 95%. So, imagine if all that asphalt were somehow changed in color to extremely reflective white, for example. What effect would that have? The area we are talking about is only around 1/2000 of the surface area of the Earth, so it figures that the effect might be limited. We can convert the 100,000 square miles into square meters of area, and multiply it by the 893 watts of solar energy coming in per square meter, to get a value of around 2.3 * 1014 watts, as being the maximum incoming radiation energy from the Sun. But since the Earth rotates, and is spherical, this actual AVERAGE energy rate is around 6 * 1013 watts, which ACTUALLY hits the Asphalt surfaces of the United States.

For comparison, this is around 120 times the TOTAL amount of electricity energy that we use up in the US! A significant amount of energy.

And if we could change the color of all that asphalt so that it reflects maybe 85% of that incoming solar energy rather than the 5% it currently reflects, that simple action of changing the color of all that asphalt could eliminate around 5 * 1013 watts of (heat) energy from BEING ABSORBED and even entering our planet's ecosystem! The fact that the light is REFLECTED means it stays in the same wavelengths, including visible and ultraviolet, which could then generally pass easily OUTWARD through our atmosphere, without having any global warming effects. A really good thing!

And being the removal of around 100 times the energy of all the electricity we use up (which all becomes heat after we use it), or around 50 times the amount of heat energy that electric powerplants throw off in the process of making that electricity, this would certainly be a wonderful step in the right direction.

Counteracting the massive energy dumping into the atmosphere of electric powerplants and much more, would be a very wonderful accomplishment!

How hard would it be to do such a thing? Maybe fairly easy! Consider the traffic markings on the highways! White lines and yellow lines are EVERYWHERE! True, some are merely painted on, but many are heat-melted (thermoplastic) into becoming part of the roadway. So imagine that instead of a four-inch wide line, the white line now at the edge of every roadway was made far wider, to cover the entire surface of the highway. (Maybe the line markings could then be black or some contrasting color.) The materials used for those lines have already been fully tested for not making the roads too slippery or wearing out too quickly, or otherwise detrimentally affecting the asphalt surface. So such a change could be done virtually next week! The plastic nature of the coating material would even reduce moisture penetration into the asphalt, probably lengthening the life of the road materials! A company in India manufactures a material they call ROMAC, which comes in bags and is heated to around 200°C and then applied in any of several standard methods, to a thickness of around 2.5 mm (0.1 inch). That would be it!


But, sadly, even this would only make a tiny dent in the immense problem of global warming. Using the energy equilibrium calculations of the first page of this presentation, we can calculate the equilibrium temperature of the Earth, with this effort at reflecting so much more of the Sun's energy out into space. It turns out to be disappointingly puny. Even though we would be greatly changing the reflectivity of that 100,000 square miles, it is still only around 1/2000 of the area of the surface of the Earth. The change in the entire Earth's reflectance (Albedo) would therefore be very small, and the calculated reduction on the equilibrium temperature would only be around 0.05°F.

We should certainly do such things, but we clearly need to do far more as well. This is a good indication of how huge the problem is! For us to change the color of EVERY highway and road in America, and every parking lot, and every flat rooftop, in having the benefit around a hundred times better than the total amount of all energy dumped into the atmosphere related to our usage of electricity, STILL only has such a miniscule effect in reducing the equilibrium temperature. It is amazing.

However, if we did this, and changed the color of all of our highways and parking lots and rooftops, maybe other countries might follow and do the same. And maybe people smarter than me will then see other and better ways to reflect more sunlight. Or other creative ways of giving us a fighting chance of survival as a species.


Human nature is really something! More than half the e-mail I have received about this concept has been VICIOUSLY NASTY! People seem to attack me for ORDERING them to do things like this, as if I want to be some Big Brother government or something!

They are clearly quite comfortable with the status quo! Nearly everyone always is! Maybe they think that someone INTENTIONALLY made asphalt black or concrete gray and that they had some profound reason for deciding on such colors! Others have told me that I would be responsible for millions of traffic accidents and thousands of deaths because drivers would not be used to such different colors. Apparently, we are to assume that all drivers are so stupid that they would be incapable of keeping their vehicles under control with this different environment. Such people must be terrified when day turns to night, or it starts to rain or snow or there is fog!

I NEVER mind receiving critical e-mails IF there is some indication that the writer THINKS or is sane! Especially if the notes are meant to suggest improvements for a presentation. But when people write in truly silly and stupid complaints, making clear that they have NO idea what they are trying to talk about, and essentially advertising that they are truly ignorant and angry, no thanks!

DID I ORDER anyone to change the color of highways above? I don't THINK so! I merely SUGGESTED one possible concept (of what I would hope may be thousands) to show ways where we MIGHT ameliorate (I put that word in just for those ignorant people! I have a strange sense of humor!) global warming.

In fact, I would never even have suggested that one EXCEPT that it is an EXISTING TECHNOLOGY which HAS BEEN SUCCESSFULLY USED FOR MANY DECADES as lane markers. Did I ever recommend making highways as slippery as skating rinks? No.

Oh, oh! What if the color change of roads might confuse migrating birds from their correct paths? Or tortoises or the chicken that crossed the road? BILLIONS of birds might die, mightn't they? Yeah, right.


This presentation was first placed on the Internet in August 2007.



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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago