Does science support the proposition that man-made greenhouse gases are leading to a climate change? In fact, the evidence for the claim that the earth has grown warmer is shaky.
Federal government statistics show no rise in temperatures. British naval records have found no significant change in temperatures at sea since the mid-1800s. The reported worldwide increases in temperature (0.5° to 1.0°F since the late nineteenth century) occurred mainly before 1940—before the rapid rise in CO2.
Even if we accept the figures showing that the world has become 1°F warmer, the computer models predict that a much greater climb in temperature should have occurred over the past hundred years than that which has been measured. Even the National Academy of Sciences is skeptical of the validity of the computer models and warns that the modeling of clouds—a key climate factor—is inadequate and poorly understood. Science magazine has documented that the models need to be adjusted to replicate the current and past climates. Recently some researchers claimed that, by including aerosols, the models fit the temperature records. Yet Patrick Michaels, a University of Virginia climatologist and a critic of global warming hysteria, has shown that the reported better fit resulted from using only a truncated portion of the record. Even with aerosols in the model, the computer results fail to track accurate temperatures over the last few years.
HOW MUCH, HOW FAST?
Virtually all climatologists agree that an increase in greenhouse gases will affect climate, although they are unsure as to how and to what degree. The theoretical predictions of temperature change have continuously been slashed as more information and better models have been developed. A decade or more ago, researchers forecast sea levels rising eighteen feet by the middle of the twenty-first century; current predictions are more in the range of six inches to three feet in the next hundred years. The 1990 Scientific Assessment from the Intergovernmental Panel on Climate Change forecast global warming at 6° to 14°F by 2050; the 1996 Assessment estimated warming of 2° to 6°F by 2100, a cut of more than 50 percent over a period twice as long. In other words, if climate change occurs, it will come at only about one-quarter of the speed of earlier predictions.
The speed as well as the magnitude of any climate change will determine its effect on the globe. Although many environmentalists have contended that the rate of change in temperature will exceed any that has occurred since the last ice age, it now appears that any warming will occur more slowly. Moreover, researchers have now determined that climate variability has been greater over the past ten thousand years than anything we have experienced during the last century and a half.
WATER AND ICE
Some predict that the warming will be very modest but that a buildup of greenhouse gases will result in increased evaporation and cloud cover. In that scenario, climate change will affect temperature marginally but will have greater impact on rainfall. If that view of warming is correct, any rise in sea levels will be small; the levels may even drop. Accordingly, even though the oceans may warm marginally and thus expand, increased precipitation and especially snowfall in Antarctica will add to the amount of water trapped in gla-ciers and perhaps lead to a net fall in water levels.
In contrast, scary news articles intimate that global warming might melt the polar ice caps and lead to a huge rise in sea levels. Most of the Arctic Ocean is covered with floating ice; if it melted it would not have any effect on water levels. The only large bodies of frozen water that, if melted, would measurably increase the height of the oceans are in Greenland and Antarctica. The glaciers in Greenland are surrounded by mountains that block them from sliding suddenly into the sea, and their melting would take centuries.
As our economy becomes more information based, will we continue to depend as heavily on fossil fuels?
The Antarctic is covered with glaciers thousands of feet thick. The West Antarctic ice sheet could be discharged into the sea, a development that might raise ocean levels by sixteen to twenty feet within a hundred years and thus be extraordinarily costly. Fortunately, the experts believe that it is also extremely unlikely. Professor Charles Bentley of the Geophysical and Polar Research Center at the University of Wisconsin writes: “In light of the evidence for recent stability, it is difficult to see how climate warming . . . could trigger a collapse of the WAIS [West Antarctic ice sheet] in the next century or two. Ice sheets take thousands of years to respond to changes in surface temperature.”
We are not only uncertain about the direction of sea levels but unclear about the future growth in greenhouse gas emissions. There is little doubt that the concentration of CO2 in the atmosphere has been rising for well over a hundred years. In 1990, the concentration of carbon dioxide in the atmosphere was measured at 353 parts per million by volume, a rise of 25 percent from the pre–Industrial Revolution figure of 280 parts per million. Human activity, especially burning fossil fuels, has contributed to this change. What is uncertain is the future. Will humans continue to depend for energy primarily on coal, oil, and wood? Certainly for the next few decades the world will derive its main source of energy from carbon-based fuels.
In the industrialized West, however, carbon dioxide production relative to national income has been declining. As our economy becomes more information based and less oriented toward heavy industry, we also become less dependent on coal and petroleum. Predictions about what kind of energy might be used a hundred years hence have little validity. Some forecast that, long before then, mankind will have run out of oil and natural gas. Coal supplies appear to be plentiful for several hundred years, but coal has other drawbacks beyond those related to CO2 emissions. Coal mining is dangerous; burning coal produces sulfur oxides that contribute to acid rain; coal burning also produces particulates that may be hazardous to human health.
The wide range of emission forecasts reflects uncertainty about future economic growth rates, the availability of cheap fossil fuels, population expansion, and whether countries will be willing to pay the costs of cutting emissions. If China were to continue to grow rapidly and to rely on its existing huge stocks of coal, carbon dioxide emissions would continue to grow regardless of whatever the rest of the world were to do.
THE HISTORICAL RECORD
The models that employ the various scenarios are poor at replicating past climate and even current weather conditions. Temperature data for the world, measured over the last hundred years, show an increase of about 1°F or less. Partisans point to this as evidence of warming, but much of that boost in worldwide temperatures occurred before 1940 and a good portion took place around 1920, before widespread industrialization. From 1940 to the mid-1970s, global temperatures declined a little, setting off speculation about global cooling. Then, starting in the second half of the 1970s, the world became warmer. Overall for this century, temperatures have risen most at night and during the winter, with a fall in summer daytime readings.
Within the United States, which has the best records, thermometers have registered no significant gain for the 101 years between 1895 and 1996. What were temperatures in 1896 compared with those of 1996? Slightly warmer! Nor has precipitation varied. The general circulation models that have been predicting warming forecast that the polar regions should warm the most. Over the last fifty-five years, no significant warming has been measured at either pole. American researchers at the South Pole, who have been keeping records for forty years, recorded the coldest month ever in July 1997.
Moreover, there are problems with the measurements used to calculate temperature trends worldwide. Those data are based on ground measurements, taken mainly in cities. Most of the world, especially the Southern Hemisphere, is water, and there are no figures for much of this area. Mountainous regions also sport few thermometers. Poor and primitive areas are underrepresented in the data since most gauges are located in the more economically advanced parts of the world.
Another major problem with the data is that, as cities grow and pave more of their area with asphalt and cement, heat is trapped, thus raising local readings. Although climatologists claim to have adjusted for this bias, questions remain about whether the record can accurately portray world temperature changes.
Furthermore, since 1979 satellites circling the earth have measured temperatures around the globe, including much of the world where no one can regularly take temperatures. Those data fail to show an increase in global temperatures over the period 1979 to 1997, even though the models predict and earth-based thermometers show a slight rise. Although the satellite figures are controversial, they are highly correlated with the readings from weather balloons, taken twice a day around the planet. Critics of the satellite figures point out that they reflect the average temperature between the earth’s surface and fifteen thousand feet. However, not only do the data from space cover the planet, but they are free from the heat-island effect and are accurate to within plus or minus 0.02 degrees.
Environmentalists view climate change as a catastrophe necessitating immediate and major steps to head off or mitigate. Whether global warming will occur is uncertain. Although temperature data until now could reflect a warming planet, they are also consistent with normal fluctuations in weather. From a scientific viewpoint the evidence for global warming must be “not proven.”