---

Rushing to Judgment
by Jack M. Hollander
Related Articles
Experimenting with Earth by V. Ramanathan, Tim P. Barnett

Is Earth warming? The planet has warmed since the mid-1800s, but before that it cooled for more than five centuries. Cycles of warming and cooling have been part of Earth's natural climate history for millions of years. So what is the global warming debate about? It's about the proposition that human use of fossil fuels has contributed significantly to the past century's warming, and that expected future warming may have catastrophic global consequences. But hard evidence for this human contribution simply does not exist; the evidence we have is suggestive at best. Does that mean the human effects are not occurring? Not necessarily. But media coverage of global warming has been so alarmist that it fails to convey how flimsy the evidence really is. Most people don't realize that many strong statements about a human contribution to global warming are based more on politics than on science. Indeed, the climate change issue has become so highly politicized that its scientific and political aspects are now almost indistinguishable. The United Nations Inter-­governmental Panel on Climate Change (IPCC), upon which governments everywhere have depended for the best scientific information, has been transformed from a bona fide effort in international scientific cooperation into what one of its leading participants terms "a hybrid scientific/political organization."...

... Earth's climate is constantly changing from natural causes that, for the most part, are not understood. How are we to distinguish the human contribution, which may be very small, from the natural contribution, which may be small or large? Put another way, is the additional carbon dioxide humans are adding to the atmosphere likely to have a measurable effect on global temperature, which is in any case changing continually from natural causes? Or is the temperature effect from the additional carbon dioxide likely to be imperceptible, and therefore unimportant as a practical matter?

Global warming is not something that happened only recently. In Earth's long history, climate change is the rule rather than the exception, and studies of Earth's temperature record going back a million years clearly reveal a number of climate cycles' warming and cooling trends. Their causes are multiple - possibly including periodic changes in solar output and variations in Earth's tilt and orbit - but poorly understood. In recent times, Earth entered a warming period. From thermometer records, we know that the air at Earth's surface warmed about 0.6ºC over the period from the 1860s to the present. The observed warming, however, does not correlate well with the growth in fossil fuel use during that period. About half of the observed warming took place before 1940, though it was only after 1940 that the amounts of greenhouse gases produced by fossil fuel burning rose rapidly, as a result of the heavy industrial expansions of World War II and the postwar boom (80 percent of the carbon dioxide from human activities was added to the air after 1940).

Surprisingly, from about 1940 until about 1980, during a period of rapid increase in fossil fuel burning, global surface temperatures actually displayed a slight cooling trend rather than an acceleration of the warming trend that would have been expected from greenhouse gases. During the 1970s some scientists even became concerned about the possibility of a new ice age from an extended period of global cooling (a report of the U.S. National Academy of Sciences reflected that concern). Physicist Freeman Dyson notes that "the onset of the next ice age [would be] a far more severe catastrophe than anything associated with warming."...