2000

Climate Flip-Flop

A recent report by the National Research Council of the National Academy of Sciences has attempted to reconcile the difference in temperature trends between surface and atmospheric observations. The surface data shows a strong warming trend, while the satellite data show a zero to slightly positive trend. The climate models, however, predict that the troposphere would warm more rapidly than the surface in response to increases in atmospheric greenhouse gas concentrations. The report noted in particular the ground-based warming observed over the last 20 years.

One explanation may lie in a natural climate cycle that occurs every 20 to 30 years, known as the Pacific Decadal Oscillation (PDO). According to the scientists at the University of Washington who discovered the phenomenon, the Pacific Ocean goes through cycles of warm and cool periods every 20 or 30 years. The years 1925 to 1946 and 1977 to 1998, for instance, were dominated by a warm phase, while cooler Pacific waters dominated the period in between. This cold phase leads to weather patterns in the U.S. similar to those produced by La Nia (Washington Post, January 20, 2000).

This may help explain global temperature trends over these time periods. The global temperature record measured at the surface shows that the years 1911 to 1945 experienced a rate of warming similar to the one from 1977 to the present. Of course, the cooling trend from 1945 to 1977 had some scientists, such as Stephen Schneider, worried about global cooling. It may be that the PDO can go a long way toward explaining many of the trends observed in the global temperature data as well as the discrepancy between the satellite and surface temperature measurements. If we are indeed entering a cold phase, winters will be colder and wetter, with a higher possibility of drought in the Southwest. This could also lead to heightened hurricane activity in the Atlantic.

In a related item, Colorado State University hurricane expert William Gray has released his hurricane predictions for the year 2000. He predicts that 11 named storms will form in the Atlantic Ocean and Gulf of Mexico this year. This heightened hurricane activity is due to “a marked shift in temperatures in both oceans, back to levels not seen since the active hurricane decades of the 1940s and 1950s,” notes the Stuart News/Port St. Lucie News (January 21, 1999). “The data reflect a naturally occurring fluctuation in ocean conditions, not a sign of global climate change.”

Climate Change Certainty Overstated

Colorados state climatologist, Roger Pielke, Sr., a professor at Colorado State University, says that people should not worry about global warming, according to the Denver Post (January 14, 2000). Pielke presented research at the American Meteorological Societys annual meeting that showed that land use change has a significant effect on the climate system that is not adequately accounted for in the climate models. “If land-use change is as important on the climate system as our results suggest, there is a large uncertainty in the future climate, since there is no evidence that we can accurately predict the future landscape,” said Pielke.

The presence of plants, for instance, influences the Earths energy budget, said Pielke. Increases in atmospheric CO₂ concentrations may increase the area covered by plants, which will lead to more transpiration. This water vapor could have one of two effects: It could cool the atmosphere directly or through cloud formation or it could warm the atmosphere as a greenhouse gas. “This is an example of a complex feedback between vegetation and the atmosphere that we do not completely understand,” Pielke said. Other influences on land use can also effect the Earths energy budget.

“Since landscape and other atmosphere-surface interactions involve complex, non-linear feedbacks, it becomes impossible to predict future climate accurately,” Pielke said. “This suggests that the scientific community might be overstating the certainty of global climate change.”