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  Наука > Геология
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Doing Something About the Climate

The Century in Review: Twain's remark about the weather is no longer a laughing matter

Mark Twain supposedly wrote, "Everybody talks about the weather, but nobody does anything about it." That got a laugh from readers in 1897—not only could nobody influence the sun and rain, but nobody could even imagine how to try. You might as well shake your fist at the law of gravity.

But what was a joke a hundred years ago is sounding more and more scary these days, because the weather might be changing, and it might be our fault. And if it's our fault, then it's our responsibility to fix it. I'm talking about the various phenomena we lump under "global warming, climate change, the greenhouse effect." That has been a scientific story throughout the 20th century, and a policy question that will dominate the 21st.

Only a year before Twain wrote his joke, the great Swedish chemist Svante Arrhenius (1859–1927) published a paper first describing what we know as the greenhouse effect. Certain gases in the atmosphere are transparent to visible light but opaque to infrared light, like the glass of a greenhouse. Thus the energy that comes down from the Sun is trapped underneath the Earth's atmosphere in the form of heat, exactly the way a greenhouse stays warm in the cold season. Water vapor and carbon dioxide (CO2) are the two most important of these gases.

Arrhenius noted that the world's developed countries were producing more and more CO2 from energy production, and he concluded that the world's overall temperature ought to rise. He calculated that if the concentration of CO2 in the air were doubled, the Earth's temperature would rise by several degrees.

This was a very far-reaching prediction, and there were no means to test it for several decades, and not all that much data either. We needed more than just weather records—we needed a basic understanding of climate. Climate is what the weather would be like if there were no weather—if all the clouds, rain, high and low temperatures, wind, and haze were averaged out for the whole season or the whole year. Climate is weather in general, and it's more than just meteorology.

Climate is the result of a complicated dance between the whole Earth system and the energy falling upon it from the Sun. Part of that energy warms up the air, but the rest warms the solid earth and the oceans. The currents in the ocean carry warm water here and cold water there, moving heat around. The continents move—for instance, when Panama rose out of the sea a few million years ago, it cut off a strong current between the Atlantic and Pacific oceans. Over thousands (not millions) of years, ocean currents seem to flicker back and forth between different configurations. Living things affect the levels of greenhouse gases in the air. The sea rises and falls for several different reasons. And all of these things affect every other thing.

Geologists have shown us what no set of weather records can—they have pieced together a good picture of how the global climate has changed over the last several hundred thousand years, and a fair picture of climate changes for some millions of years before that. The scary thing this record shows is that world temperatures sometimes have shifted drastically in just a decade or two, going from warm to cold or cold to warm—and staying there for thousands of years. William Calvin calls this "the great climate flip-flop." CO2 has fluctuated too. But nowadays, as Arrhenius foresaw, CO2 is well on the way to doubling.

Computer models can't deal with such a complex situation. They are a fantastic achievement and getting better all the time, but they can't yet model the kind of behavior that we know has happened.

One of my favorite scientists, Wallace Broecker, has spent his life exploring this field: "Whatever pushed Earth's climate didn't lead to smooth changes," he has written, "but rather to jumps from one state of operation to another. So the question naturally arises, What is the probability that through adding CO2 we will cause the climate system to jump to one of its alternate modes of operation? I contend that since we can't yet reproduce any of these jumps in computer simulations, we don't really know how many modes of operation Earth has, and we certainly don't have any idea what it might take to push the system from one to another. . . . So we're entering dangerous territory and provoking an ornery beast. . . .

"My lifetime study of Earth's climate system has humbled me. I'm convinced that we have greatly underestimated the complexity of this system. The importance of obscure phenomena, ranging from those that control the size of raindrops to those that control the amount of water pouring into the deep sea from the shelves of the Antarctic continent, makes reliable modeling very difficult, if not impossible. If we're going to predict the future, we have to achieve a much greater understanding of these small-scale processes that together generate large-scale effects."

But you can't tell any of this from what they say on TV, from soundbites, or from any one source on the Web. Much of what's there is simply political literature. Greenpeace is sure of its facts (although it wrongly states that carbon dioxide, not water vapor, is the most significant greenhouse gas) and sure of its enemies. And on the other side the Greening Earth Society is happy to tell you its version of the facts (though it wrongly states that extra carbon dioxide in the air can do us only good) and is eager to attack its enemies.

The situation is uncertain, and humans hate uncertainty. But for a precise description of our uncertainty, I recommend the latest policy statement on climate change from the rigorously scientific American Geophysical Union.

When it comes to climate, the whole world has changed over the last hundred years. What was distant speculation has become an urgent political problem—what must we do about the global climate given what we know? And Mark Twain's joke is no longer funny at the end of this century.


I recommend the papers of Wallace Broecker. Since publishing the piece I quoted, he has refined his speculations in the pages of GSA Today. He also has interesting things to say about oxygen and his experience in turning the Biosphere into a proper science experiment.


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