Two ways to think cool

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By Kirsten Peters

Dogs pant with their tongues hanging out, young men sweat by the bucket and aging geologists just fall over on our faces in the shade on a hot summer’s day. But is there a way we could choose to cool the whole planet in a few decades if we really need to?

Global warming may or may not be our greatest problem in the 21st century. But if it is, there are two ways we could potentially lessen warming. One is exotic, but would address the worldwide problem of warmth. The other is more closely attuned to practical matters and common sense, and would help us limit heat increase that’s so prevalent in and around cities — where most Americans live.

Here’s the global picture:

Astute readers of the news media know that each time there is a major volcanic eruption – like Mount Pinatubo in the Philippines in 1991 or Mount St. Helens in my own fair State of Washington in 1980 — the Earth cools. Pinatubo, for example, cooled the whole world by about one degree Fahrenheit. The effect lasted about a year. In strong cases, the volcanic cooling impacts agriculture and generally decreases crop yields – which is why it shows up in the news and normal people, not just us rock-heads, hear and care about it.

Volcanoes act as year-long cooling agents primarily because of the sulfate in their eruptions, tiny bits of which make it up to Earth’s stratosphere with the force of the blast. We humans also create sulfate particles in the air when we burn coal. That’s because coal, especially nice, cheap coal, has quite a bit of sulfur impurities in it.

Our coal-based sulfate in the air sometimes stays much closer to the ground and contributes to acid rain just downwind of smokestacks, but some of it gets carried upward, too. In either case, it acts as a bit of sunscreen that lowers temperatures.

There are now a few serious proposals about doing more, not less, sulfate “pollution” of the upper atmosphere. If global warming becomes severe, the argument goes, we could launch sulfate into the stratosphere to mimic the natural volcanic effect and lower global temperatures. The “solution” would tend toward the global. The work would have to be done each year, again and again, but all sorts of launching devices could be employed, including relatively cheap devices like airplanes, balloons, and perhaps even battleship guns.

I doubt it will ever come to that, partly because we could expect crop yields to drop. But I do think we could become smarter about a simple matter that would make our cities and suburbs cooler — and actually cool the planet just a bit as well.

Here’s a simple fact: dark colored objects warm up a lot more in sunlight than light colored ones. And, as you know, many roofs are dark: gray-black or dark brown asphalt shingles are popular on houses, black tar on flat roofs, and my own personal favorite, dark slate on a few roofs of historic stonewall houses back East.

What all these roofs have in common is that they warm up greatly when they are bathed in sunlight. That makes for hot roofs, but also for hot air all around the roof during the summers – thus contributing to hot cities and suburbs from Memorial Day to Labor Day.

You can actually see the effect in weather reports during the summer. Temperatures in the country on scorching days in July are routinely lower than in the suburbs and land-locked cities. That occurs for several reasons, including that the country is full of plants that are pumping water up into their leaves where it evaporates (and us country bumpkins stay cool because of it). Meanwhile, cities and suburbs show mostly roofs to the sun — and bake all afternoon long because of it, achieving higher and higher temperatures.

If summer heat turns out to be our greatest trouble, we might be well advised to think about light-colored roofing.  One white roof is like one small bit of snow lingering on the Earth’s surface all summer long, reflecting a great deal of light and energy — so, one roof at a time, we could actually help the whole Earth.  


Dr. E. Kirsten Peters is a native of the rural Northwest, but was trained as a geologist at Princeton and Harvard. A library of earlier Rock Doc columns is available at www.Rock

Doc.wsu.edu. This column is a service of the College of Sciences at Washington State University.