Referring to "Earth in the Balance," his 1992 compendium of environmental alarms, Al Gore recently said, "There's not a statement in that book that I don't endorse. Not one. The evidence has firmed up the positions I sketched there." Positions such as:

"The climate changes that we are now bringing about by modifying the global atmosphere are likely to dwarf completely the ones that caused the great subsistence crisis of 1816-19, for example, or those that set the stage for the Black Death," and "are likely to be five times larger than the fluctuations that produced the Little Ice Age, for example, or the global climate change that led to the Great Famine of 1315-17."

Gore's eco-pessimism helped produce the 1997 Kyoto Protocol, which assigns to nations vastly different duties to reduce carbon emissions responsible for global warming. America's duty under this agreement (which the Senate is not about to ratify) would be to reduce carbon use by 550 million tons per year in 2010. That might mean reducing by 40 percent the use of coal and oil.

Before policymakers undertake trillions of dollars in abatement costs, they should consider evidence that does not "firm up" Gore's thesis. Consider a booklet published by the American Enterprise Institute, "The Greening of Global Warming" by Robert Mendelsohn of the Yale School of Forestry and Environmental Studies.

He says that in the past decade our understanding of the effects of climate change has undergone a "near revolution" because the natural science and economic analyses underlying predictions have "altered dramatically." Science foresees milder climate scenarios. Ecologists are shifting from predictions of "ecosystem collapse" to long-term predictions that include benefits:

"These changes are so dramatic that it is not clear whether the net economic effects from climate change over the next century will be harmful or helpful. The new research further suggests that . . . many countries will benefit from warming--the very countries, ironically, that have contributed the most to historic emissions."

Gore's 1992 strictures about global warming reflected the 1989 assessment by the Environmental Protection Agency, which influenced subsequent studies that concluded that damages from climate change would be, Mendelsohn says, "universal and devastating."

The predicted (by the EPA) doubling of greenhouse gases was projected to produce temperature increases between three degrees and six degrees Celsius. Sea levels would rise one meter, many tree species would disappear (e.g., maples would die off in southern New England), and all animal species, and especially endangered ones, would be stressed. Sharp reductions of precipitation during growing seasons would be one reason why many crops would suffer 30 percent to 40 percent reductions in yields. Beneficiaries of warming would be pests that would ravage crops and trees, and diseases borne by insects. Timber scarcities, increased water pollution due to insufficient dilution by runoffs, huge costs for sea walls and for energy for cooling--the litany of woes was long.

Now improved analyses--of the interaction of oceans and atmosphere, of the cooling effect of sulfates found in the atmospheres of northern industrial countries, and much else--support the conclusion that warming will be only one degree to 3.5 degrees Celsius. Precipitation will increase, as will many plants: The average crop would be 30 percent more productive with projected increases in carbon dioxide.

"There is," Mendelsohn writes, "an unstated myth in ecology that natural conditions must be optimal. That is, we must be at the top of the hill now." The myth is sometimes sustained by discounting the potential of societal adaptation, such as that which controlled the malaria that used to afflict travelers along the Ohio River.

People with Gore's turn of mind--people who seem to relish environmental threats as reasons for expanding government's supervision of all behavior--have not really been happy since the putative "energy crisis" of the 1970s. Of course, predictions of the coming exhaustion of oil reserves have been hardy perennials .

Alex Taylor III, writing in Fortune, notes that in 1874, just 15 years after Col. Edwin Drake drilled the first oil well in Pennsylvania, the state's chief geologist said that the use of kerosene for lighting would drain U.S. petroleum reserves by 1878. "In 1939, and again in 1951, the Department of the Interior added up all the reserves in the world and reported, both times, that 13 years of oil remained." One reason more oil has been found this year than in any other year this decade is that offshore drilling, which was done in only 300 feet of water in 1965, will soon be done in 10,000 feet.

Never in recorded history have birth rates been as low, or per capita food production as high, as at the moment. Gore must pray for relief from the accumulating evidence that Earth is not really hanging in precarious balance.