Another question concerning climate change ...

[Mike Peregrine]

Started to post this in Patrick's thread, but it didn't really belong ...

I've had a question lately that I wonder if anyone knows anything about or whether it has been explored much scientifically or what the going thinking on the subject may be ...

The other day the air temperature was cold - in the low 20s here ... well below freezing. There had been some light snow the night before that had accumulated along the edges of the streets. The sunlight was striking the street and enough heat was radiated by the concrete surface to melt the snow, in spite of the cold temperatures. Now we've all seen that and it's nothing special. But my question is ... considering the industrialization of the modern world and the fact that man has now covered the planet in a web of concrete road surfaces and structures, would there be any way that this could contribute to warming? The planet used to be covered in more areas of green vegetation, which takes sunlight and absorbs it in the the creation of energy. As man has spread, so has the effects he has in clearing vegetation and through poor land management, the size of desert areas has increased, which also creates a spread over large areas of lighter colored soils and sand ... possibly radiating more heat directly into the boundary layer air than it absorbs. Hope this makes sense. What I'm wondering is whether it's not just a C02 emission question, but also the types of surfaces that have increased earthwide that are more likely to radiate heat rather than absorb it - sort of the same way clouds radiate sunlight back into space ... but this is at surface level.

Maybe this is part of the heat island effect that Jim talked about in the other thread - but I would think that not only urban areas would contribue to the overall effect it would have on warming ... the road network alone is extremely vast - - - anyway, just wondered about it.

 

[Jeff Snyder]

It is possible, particularly in those areas that are built-up over a very large area (like the New England area). Any drive through the plains will reveal that only a very very small area of the land is builtup (asphalt, shingles, etc), as you can drive for hours between larger population areas. Some of the major roads (interstates) are concrete, which is lighter in color than even some natural land areas (like forests), in which case I'd think that the higher albedo would actually lead to a cooler local area. Remember, in many cases, lighter color means higher albedo and more solar energy that is reflected back into space; dark areas have lower albedo, so more insolation is absorbed by the surface (allowing the surface to warm, or dry if it's wet, which then warms the air above it -- i.e. sensible heating). This is much the reason why it can be VERY hot immediately above a blacktop road during the summer. The blacktop areas, and many larger cities, do locally warm the low-levels I think, and this heat-island effect (including any potential impacts on precipitation downstream) is partially understood.

 

[Mike Peregrine]

Thanks for these excellent responses. I had a feeling that something along this line of study probably existed, but hadn't heard a thing about it yet or even how it is labeled. I wonder why it isn't presented as an alternative possibility in any of the publicity or articles I've read.

Chris' explanation of the presence of moisture in the scenario seems logical. When I lived in NC, the dense foliage seems to make a big difference in how tolerable the summer air feels ... the moisture released during photosynthesis releases latent heat during evaporation, so the air beneath the trees is often pretty pleasant, even on the hottest days.

And even though you might have more of a noticeable regional effect in areas such as New England or Japan, this still contributes to the sum total of all the parts. Even though the plains are not nearly as developed, if you were to lay all of the interstates, country roads, parking lots and concrete surfaces side by side, I bet the land area covereage would be staggering to consider. And here there is not as much tree covereage or overhanging vegetation to inhibit the heat radiation back into the environment. I just bet there's a measurable effect of some kind even here.

I would also think that the TYPE of surface involved would play a heavy role. For example - heat radiating from an asphault roof ... a darker color, but the type of surface seems to encourage the release of heat energy into the environment, whereas a ceramic roof may be inclined to store more of that energy, or release it in a different way than asphault might.

 

[Mike Peregrine]

Have you been able to find much data to support any conclusions concerning how the heat island effect might encourage/discourage convection? This is pretty interesting too ... so let's say heat island encourages updraft, which encourages convection ... then would the ultimate result mean greater convective coverage? - Because convection is an enormous mechanism for releasing heat energy, so this would all play into the overall equation as well. What an interesting question for thesis work - - -

At the same time, I wonder if heat island may end up discouraging convection too. Let's say you have a large urban area sprawled across the plains. Convection occurs partly because a parcel of air becomes heated and buoyant and begins to rise. But if you are dealing with a large enough 'heat island' area, you would have more or less equalized heating (I would think - just talking out of my butt here), so less of a chance of one parcel rising in favor over another. Would size of the urban area make any difference?