Tuesday, June 17, 2008

He wants to fix warming

kw: book reviews, nonfiction, global warming

I have been hearing about the "greenhouse effect", now usually called "global warming", quite literally all my life. It was one of the first scientific concepts that was explained to me in a way I could understand, about the age of seven or eight. I have always understood that "greenhouse gases" such as CO2 trap more heat in the atmosphere.

It is really simple: light of all colors, visible and invisible, but heavily weighted around a peak in the yellow-green part of the visible spectrum (between 0.5 and 0.6 micrometer wavelength), passes through the atmosphere to strike the earth or the clouds above it. A lot of the light just bounces off and goes back into space; the rest raises the temperature of the ground. That warm ground, primarily within 50° North and South of the Equator, radiates infrared upward. This radiation covers a very broad band centered around the "far infrared" wavelength of 12 micrometers (your somewhat warmer body naturally radiates nearer to 11.5 micrometers). The Sun doesn't send much radiation in these wavelength ranges downwards.

Now, suppose you put a big filter in the sky that blocks radiation between 9 and 15 micrometers, just reflects it right back to the ground, but lets all others pass. The same amount of sunlight (minus a tiny bit of far infrared) comes down, but less infrared goes up. To restore the balance, the ground has to heat up until the amount going back up, now only in the ranges shorter than 9 and longer than 15. The concept is simple. The math is not so simple: Svante Arrhenius calculated in the 1890s (no computers to help—it took him a year) that raising CO2 a certain amount—enough to effectively "shut the window"—would boost the earth's average temperature by four or five °C (7-9°F).

Simple, but with a proviso: heat transfer is energy transfer. Adding energy to the earth's near-surface systems adds energy to all of them, mainly winds, ocean currents and storms. The more energy that goes into the "motion systems", the less goes into raw temperature. And nobody has figured out what the balance is between faster currents, bigger windstorms, and temperature.

There are sure a lot of educated guesses out there, though. Collect the best of the guesses and add them to the things we do know with some confidence, and a talented scholar like Wallace S. Broecker can produce Fixing Climate: What Past Climate Changes Reveal About the Current Threat and How to Counter It. Dr. Broecker and co-author Robert Kunzig present a solid synthesis of the best pro-"warming is a threat" thinking, and add a few chapters of "what can we do about it?".

Take a good look at this chart, a record of the four ice ages of the past 400,000 years, measured from the ice core drilled above Lake Vostok in Antarctica. The dates are pretty reliable, because you can count yearly dust bands.

The blue line is relative global temperature, measured by ratios of Oxygen isotopes. see the book for how these work. I find the jaggedness of these curves to be of great interest; there is a large variation on a scale of one to two thousand years evident during the cold periods. During the warmer "interglacial" periods, warm/dry and cool/wet swings on a similar time scale also occur; the most recent cooling was the "Little Ice Age" (LIA) that ended in the late 1800s. Valley Forge was an awful place in the winter of 1775, just ask George Washington. It is relatively pleasant today. But it was even nicer 1,000 years ago, though you'll have to find a long-lived Iroquois to ask.

The green line is measured Carbon Dioxide abundance; on the scale given, the modern amount of 380 ppm is literally an inch of so off the chart. The red line is dust. It is no surprise that the coldest periods were the dustiest.

I don't have a chart to show the eight "Bond Events" that have occurred in the past 11,000 years, but some of them included cold worse than the LIA and heat greater than the present time of "record heat waves". Broecker and Kunzig don't mention Bond Events.

That doesn't mean they are wrong, though. I think human releases of CO2 really are adding to the heat load of Earth's surface, atmosphere and oceans. I just don't think it is all bad news. I have on hand a report, the Global Agro-ecological Assessment for Agriculture in the 21st Century by Fischer, Shah, Velthuizen and Nachtergaele. In its section on cultivable land (p13), we find that only Asia is using all the land available to it for food. The two areas with the most potential for expanded farming are Africa and South America; a distant third and fourth are Europe plus Russia and North America.

There is no comparable chart for the expected changes with a warmer climate, but there is a table on p23 with some estimates. Basically, because rainfall will increase in most areas, even though certain major desert areas will expand, they predict that global agriculture will be slightly more favorable, with these extrema:
  • For Europe, Russia, and North America, the warmer the better.
  • South America will experience the greatest decrease of cultivable land (10% to 20%).
  • Africa will experience a modest decrease.
  • Asia and Oceania will be little affected.
What nobody says enough about is which crops will be favored or disfavored. All crops do better with more CO2 in the air, but Rice does the best. Farmers who are well enough off feed the gas to rice paddies, where it is found that ten to twelve times the "ordinary" amount of ambient CO2 gives bumper rice crops. Maize and sugarcane are little affected, because they use C4 photosynthesis, which can make effective use of even one-fifth the "ordinary" amount of CO2. (In my opinion, C4 photosynthesis is the prime driver of glacial cycles, since such plants became widespread in the Pliocene: more grass = more ice.)

Dr. Broecker's analysis in the last few chapters of the book is most captivating. He discusses, and eliminates, nearly all "alternative energy" as a short-term solution. He settles on Carbon Dioxide Sequestration for both long- and short-term potential, though he holds out little hope that Americans will have the political will to do much about it.

He makes one stunning comparison: Firstly, the amount of CO2 we must gather yearly for "total offset", if liquefied, would cover Manhattan Island almost a quarter mile deep. However, and secondly, the amount of wastewater we treat in the US every year would cover Manhattan twice that deep. The infrastructure to treat that water was all built in the past forty years. So the infrastructure to "do a job" on the sky is but half as grand. It is quite doable. This is the kind of image I'd like to see made much more of, publicly. It is likely that we'll want to do something to counter our gassing-up of the atmosphere, at some point. It is doable.

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