A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Man Wrecks Planet: Are the popularly published environmental statistics accurate?

June 20, 2003

Dear Cecil:

I engage in some modest activism on behalf of the environment and a few other causes and I am sensitive about having my facts straight. I keep coming across the following provocative statement: "Today we added 265,000 babies, lost 7,500 acres of rain forest, added 46,000 acres of desert, lost 71 million tons of topsoil, added 15 million tons of carbon dioxide to the air, lost about 70 species — and we get to do it again tomorrow." Certain of the numbers given seem plausible; others seem possibly inflated. What's the straight dope here?

Cecil replies:

As a rule, R.T., you want to distrust any statement printed on a T-shirt, which is where you'll usually find this one. (Principal exception: "I'm with stupid.") But this stuff isn't as off-the-wall as most wash-and-wear propaganda — in fact, if you allow for the inherent imprecision of global environmental statistics, many of the numbers correspond reasonably well with current scientific consensus.

The statement you keep seeing is a paraphrase of the opening lines of Ecological Literacy: Education and the Transition to a Postmodern World by David W. Orr (1992). Orr, who's more of a philosopher than a scientist, provides no cites for his statistics, but I was able to track them down:

  • Today we added 265,000 babies. Close enough. According to the International Programs Center of the U.S. Census Bureau, world population as of October 2002 was increasing by 209,000 per day — 361,000 births offset by 152,000 deaths.
  • Lost 7,500 acres of rain forest. You're the victim of a typo. The most common version of the quote says that 75,000 acres of rain forest are lost per day. (Orr wrote 115 square miles, which is about the same.) Even that number may be low. Based on data compiled in 1990 by the U.N. Food and Agricultural Organization, the world's tropical forests are disappearing at an estimated rate of 38 million acres per year, or 104,000 acres per day.
  • Added 46,000 acres of desert. Close. In 2002 UN secretary-general Kofi Annan said that "6 million hectares [15 million acres] of productive land are being lost because of desertification" annually, which works out to 41,000 acres per day.
  • Lost 71 million tons of topsoil. Possibly low. Lester Brown of the Worldwatch Institute estimated in 1992 that 24 billion tons of cropland topsoil are lost annually worldwide, or 66 million tons per day. However, environmentalist and author Bruce Sundquist, reviewing the literature on the earth's "carrying capacity" (home.alltel.net/bsundquist1/se1.html), comes up with a net topsoil loss rate of 78 billion tons per year, or 215 million tons per day.
  • Added 15 million tons of carbon dioxide. Another error. The substance of importance here is carbon, not carbon dioxide. In a column back in January we established that humans on balance add as much as 1.5 billion tons of carbon to the atmosphere annually. Some of that may be removed by terrestrial "carbon sinks," but that hasn't been definitely established. If instead all the carbon stays airborne, we're adding more than 4 million tons per day (which would be 15 million tons of carbon dioxide if it were all in that form — but it isn't).
  • Lost about 70 species. No number can be confidently assigned to daily species loss because we don't know how many species there are now. Orr sought to acknowledge this in his book by saying that on a typical day 40 to 100 species were eliminated. The T-shirt maker evidently figured that this subtlety would be lost on the average T-shirt reader and split the difference. Even the range given by Orr inadequately conveys what a wild-ass guess we're talking about here. Harvard scientist Edward O. Wilson, one of the leading authorities on biodiversity, estimates that the number of species is between 10 and 20 million, of which a mere 1.5 to 1.8 million have been described. We have no direct knowledge of how many are becoming extinct; it's hard enough keeping track of mammalian extinctions, and most species are bugs and microbes. However, since species loss is tied to habitat loss, Wilson's back-of-the-envelope guess is that, assuming 10 million species in the rain forests, we could be losing 27,000 per year, or roughly 75 a day. Wilson also puts it another way: current species loss due to human intervention is probably 1,000 to 10,000 times greater than what would occur naturally.

Of course it's possible that all the distinguished professors, UN agencies, and so on are mistaken and that environmental deterioration isn't as bad as it seems. But it's not a good sign when you check out T-shirt quotes and find that things aren't merely as grim as the doomsayers would have you believe — in some cases they're worse.

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