The current argument about the fate of the Earth is not exactly characterized by its narrowness or precision. One day a new report says global warming is underway and all but irreversible. Another report speculates that a tanker full of iron filings in the southern ocean could fertilize enough algae to rival the biomass of the Amazon rain forest -- and so roll back the greenhouse effect.
In the spring, Congress passes a $30 billion Clean Air Act; in the summer, a soil scientist ventures that $500,000 a year would be enough to lime every lake in New York and New England sufficiently to restore their habitability to fish. The great division of opinion among those who concern themselves with planetary affairs often seems to be between a sense of bottomless despair and one of boundless efficacy.
This conflict is apparent in the recent works of a pair of leading lights of opposing camps. Herman Daly, a Louisiana State University professor who has for several years been serving as chief environmental economist of the World Bank, has with coauthor John Cobb published ''For the Common Good: Redirecting the Economy Toward Community, the Environment and a Sustainable Future'' (Beacon Press, $24.95). And Julian Simon, a University of Maryland professor who for 20 years has been among the most effective critics of the full-throated environmentalists, has published a collection of his popular articles, reviews and talks, called ''Population Matters: People, Resources, Environment and Immigration'' (Transaction Publishers, $34.95) as well as a more scholarly tome, ''The Economic Consequences of Immigration.''
Daly and Cobb, economist and theologian, offer a relatively comforting and familiar version of what life should be all about. They flirt with calling for a ''return to socialism,'' but settle instead on the Catholic Church critique of socialism and capitalism, with its emphasis on the person as a member of a community. (Both writers are Protestants.)
''The scale of human activity relative to the biosphere has grown too large,'' they write; the enemy of sustainability is growth. They devote an appropriate amount of effort to deflating the elaborate rhetoric of growth. The first quarter of the book is a critique of neoclassical economics. A substantial appendix presents an alternative to gross national product or growth accounting.
Much flows out of this, and some of it is sophisticated economics -- the discussion of the kind of national tax system that would be conducive to a steady state makes fascinating reading, as do discussions of the illusive concept of the ecological ''carrying capacity'' of particular regions of land.
But as gentle and genteel as is the Daly-Cobb critique of our highly individualistic society, it is not altogether clear that they envisioned a persuasively better way. ''We are glad that China's leaders saw the error of laissez-faire individualism, and we hope for a reversal of recent trends in the United States,'' they write at one point.
Also on their agenda: highly managed trade, regional decentralization and the resettlement of the countryside by the family farm. These are all in some sense desirable goals, but perhaps Daly and Cobb underestimate the importance of achieving them by consensus. Or perhaps that is precisely the point of their concluding chapter on religious vision.
Simon, on the other hand, has little use for the concept of limits. He quotes the physicist Freeman Dyson approvingly: ''Boiled down to one sentence, my message is the unboundedness of life and the consequent unboundedness of human destiny.'' And the chronicle of Simon's jousts with doomsayers over one issue after another makes for illuminating reading. He's crossed swords with practically every environmental prophet in America during the past 20 years -- over disappearing farmland, global famine, vanishing wildlife, illegal aliens, population policies and the rest. He's won far more battles than he's lost.
On balance, I think I prefer Daly. We don't need more permissions -- to multiply our numbers, to greatly alter our environment, to diminish the species population of the Earth, to divide our labor ever more intricately -- nearly so much as we need warnings that there are environmental limits somewhere and that we are surely reaching them. Never mind the Second Law of Thermodynamics -- to live harmoniously with nature seems to be one of the truly universal human imperatives, as intuitively obvious in South America as it is in Asia, North America and Africa.
Surely the preservation and conservation of the ecosystem will become ever more important during the unprecedented knitting-together of the nations of the world during the next 50 years.
But let the last word on the subject belong to Julian Simon. His point, after all, is that whatever we need to do can be done. It is true that more people increase demands on the global system, and so disturb it more, he says. But more people also have brought about better understanding of the system and greater ability to bend it to our will.
''The difference is between a world of 10,000 people many millenia ago, who inadvertently disturbed little and could not intentionally alter much, and as we are many billions now, who disturb much but who can purposefully alter even more.''
David Warsh is a columnist for the Boston Globe.