Are humans about to kill the Earth, or is it the other way around?


Is Earth fragile and vulnerable or tough and ruthless? Is it possible for us to trash a whole planet? Or is it about to trash us?

"Gaea, as I see her, is no doting mother tolerant of misdemeanors, nor is she some fragile and delicate damsel in danger from brutal mankind. She is stern and tough, always keeping the world warm and comfortable for those who obey the rules, but ruthless in her destruction of those who transgress," said James Lovelock, originator of the idea that Earth is one integrated organism. (Gaea is from Greek mythology; Earth was personified as mother of the Titans.)

The little upstart species that labels itself "Man the Wise" may be crushed by the revenge of a huge, angered planet. That's one way to look at our current predicament.

Then there's the other way, the fragile-Earth theory, often expressed by astronauts and cosmonauts looking down from space. Cosmonaut Sigmund Jahn of East Germany: "Before I flew, I was already aware of how small and vulnerable our planet is; but only when I saw it from space, in all its ineffable beauty and fragility, did I realize that humankind's most urgent task is to cherish and preserve it."

U.S. astronaut Loren Acton: "There, contained in the thin, moving, incredibly fragile shell of the biosphere, is everything that is dear to you."

As far as we know -- and we probably do not know enough -- the answer to whether Earth is fragile or tough is yes, both. Relative to most of the energy and material flows on Earth, the machinations of humankind are puny. The planet's powers are much, much bigger than our own. But in a few sensitive places we are making an impact on a planetary scale, and that impact is not a good one.

Take energy, for instance. The human economy runs on a power flow of 10 trillion watts, trivial compared with the 80,000 trillion watts that flow to Earth's surface from the sun. In the global energy picture we are hardly noticeable.

But the fossil fuels we burn have given off enough carbon dioxide to raise the atmospheric concentration of that gas by 35 percent so far. We can have such a great effect only because carbon dioxide is a minor gas (0.03 percent of the atmosphere). Minor though it is, however, it happens to be positioned (in wavelength terms) right where it blocks the outflow of heat from Earth. That 80,000 trillion watts flowing in from the sun has to flow out again. If it is blocked, Earth will heat up.

Which is to say, our energy use is trivial, but it throws a monkey wrench into a critical valve that adjusts the heat balance of the whole planet.

We make only about a million tons of chlorofluorocarbon, or CFC, gases a year, inconsequential compared with the 50 million billion tons of the whole atmosphere. And not even much compared with the thin veil of ozone in the stratosphere. But that ozone layer is another of Earth's delicate points, and chlorine released from those CFCs happens to destroy ozone without being destroyed itself. A little goes a long way. One chlorine atom can destroy at least 100,000 ozone molecules.

A mere 30 years of human CFC production has reduced stratospheric ozone by 3 percent in the tropics, 10 percent at mid-latitudes and 50 percent at some times of year at the South Pole. That could be serious, because ozone protects all life from destructive ultraviolet radiation from the sun.

We are causing that problem not because we are big and tough, but because we produce a few unusually powerful chemicals that Earth has never seen before and that happen to attack a small stock of a critical atmospheric gas.

For another example of our smallness-bigness, take water. Humans use directly only 0.7 percent of the 500,000 cubic kilometers of rain that fall each year. But of that massive rain flow, most falls on the oceans or runs off the land in floods. Only 9,000 cubic kilometers is dependable base flow of Earth's accessible rivers. We use 3,500 and pollute another 3,000 -- that is, we use or spoil more than two-thirds of Earth's accessible freshwater runoff.

So what? We have no idea so what. We know about the immediate problems we cause ourselves and other living things because of water scarcity and pollution. We do not know whether our water pollution and diversions can disrupt entire planetary functions. They might, because water is tied together with energy, and water and energy are the drivers of weather, and weather is another global phenomenon that is hypersensitive to small disruptions.

Our fertilizer factories fix 90 million tons per year of nitrogen from the air into nitrate and ammonia for the soil. That's about as much as all nature does, which is to say that we are doubling the flow of the natural nitrogen cycle. The result is population explosions of some soil organisms, die-offs of others and nitrate pollution of rivers and ground waters.

We dig phosphate out of Earth, also for fertilizer, and release it to the environment eight times faster than nature does. That creates, among other effects, green-Jell-O lakes clotted with algae blooms and dead fish. Human-generated nitrogen and phosphate flows run nature on supercharge, somewhat like revving the body up on a diet of pure sugar.

By processing ores and burning fossil fuels, we release sulfur dioxide six times faster than nature does. The result is acid rain.

We mine mercury at a speed about equal to its natural rate of weathering from rocks; cadmium at a rate 30 times faster than natural weathering; lead 10 times faster. Deposits on the Greenland icecap show that the lead content of the atmosphere increased five times between 1750 and 1940, and four times more since 1940. The lead content of the open ocean has increased three to five times since the introduction of lead-based gasoline.

Are those big effects or small ones? In tons of materials they are no big deal. Gaea releases minerals from rocks thousands of times faster than we do. But mercury, cadmium and lead are toxic heavy metals, no problem to the physical planet but deadly to most forms of life.

And life, after all, is what we are interested in. We are dependent not so much on Earth, the third planet orbiting the sun, as on Gaea, the integrated system that includes, sustains and is shaped by life.

Ecologists calculate that Homo sapiens now appropriates 25 percent of the net photosynthetic product of Gaea -- which is to say 25 percent of the energy that powers all life (40 percent of the energy that powers life on land). We do that not only directly, harvesting the food, fiber and fuel crops revved up by our fertilizers, but indirectly, suppressing biotic potential through spills and sprays, burning and paving, acid rain and heavy metals. And we expect our population to double within 40 more years and our economy to double sooner than that.

The tiny fraction of Earth's energy that flows through life is the most important and sensitive point of all, because it powers the improbable chemistry that gives our planet, alone of all planets we know, an oxygen atmosphere, a nitrogen cycle, an ozone layer, an ocean with a constant concentration of salt and a greenhouse effect large enough to keep that ocean from freezing and small enough to keep it from boiling away.

James Lovelock came up with the idea of Gaea when he looked at the atmosphere of Mars (before we had sent space probes there) and predicted confidently that there was no life there. Its atmosphere was in the perfect chemical equilibrium of a dead planet. Earth's atmosphere, in contrast, could be possible only if living things at every instant were interfering with its chemistry, bringing forth a strange, chemically unstable yet constantly regenerated mixture of gases, which proclaim to all the universe that here burns the elegant slow flame of abundant life.

That is the flame we are appropriating, redirecting, supercharging in some places and snuffing out in others. We humans, even at our collective worst or best, are nowhere near powerful enough to destroy a whole planet or to save it. With our swelling populations and industries, however, we are becoming powerful enough to destroy or save the living balance, the cycles regeneration and rebirth that are created by and that support Gaea's many forms of life -- including ourselves.

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