Cities behind warming trend: Urban weather stations give wrong impression of actual temperature
Sunday 13 October 2002
At the end of September, Arthur DeGaetano, a Cornell University climatologist, reported that Americans suffer 10 more hot summer nights than they did 40 years ago, but only "if they live in or near a major city." In rural areas, the average increase has been only two or three more hot nights.
"This means that cities and suburbs may be contributing greatly to their own heat problems," says DeGaetano. He won't dismiss completely the theory that human activities are creating a more general global warming. He leaves room for doubt that "greenhouse gases could be a factor, but not the one and only cause."
"Natural climate variability," the kind that has always existed -- industrialization or no industrialization -- is, according to DeGaetano more likely a cause.
For instance, "you tend to see higher temperatures during periods of drought," he says. After examining temperature trends over the past century from weather stations across the U.S., DeGaetano concluded areas experiencing drought recorded higher average daily temperatures, but that temperatures returned to near normal values when the rains returned.
This latter observation is inconsistent with the predictions of the global warming alarmists and their elaborate computer models. They hold that the planet's temperature is rising fairly consistently, and droughts are becoming more widespread and longer-lasting. The rise is causing the droughts. And that without drastic curtailment of human emission-producing activities, the trend is irreversible.
DeGaetano found, instead, that temperature rise followed the onset of drought, rather than vice versa, and that temperatures tend to fall once droughts end.
But the most startling finding of his study, which will be published in a forthcoming issue of the Journal of Climate, is the vast difference between higher temperatures at urban and rural weather stations. "I expected maybe a 25 per cent increase for the urban areas compared to the rural ones," DeGaetano said. "I didn't expect a 300 per cent increase."
The most likely cause of this difference is the urban heat island effect. Industrial, commercial and personal activity in cities makes cities warmer places than fields, farms and villages. Cities also give off more of the incoming solar radiation they absorb each day.
This effect could be behind the false impression that the globe is warming. More than three-quarters of weather stations in the industrialized world are in large urban centres. But as people have moved from farms to cities over the past century, in all industrialized nations, cities have grown up around the majority of weather stations. This advance of development itself has, as DeGaetano observed, caused the temperature readings in cities to skyrocket more than three times faster than the readings at rural stations. And since 75 per cent or more of weather stations have experienced this phenomenon, it has given overall global temperature observations (which are still predominately drawn from industrialized countries) the appearance of a worldwide warming. Miami and Los Angeles, DeGaetano found, have experienced "exponential" increases in temperature in the past century. New York has experienced almost none.
That's because 100 years ago, both L.A. and Miami were small towns. But the weather station in New York, in Central Park, was already surrounded by a major city then.
If you doubt the importance of the location of weather stations, consider this finding from an unrelated study by University of Alabama at Huntsville climatologist John Christy. Christy has combed through every temperature reading in his state over the past 108 years and found that the times of day at which readings are taken at multiple locations, or the varying methods by which they are taken, or the reliability of the temperature takers (many early readings were "fudged"), can make a difference of as much as one-tenth of a degree Celsius, per decade, statewide in temperature readings, or about the same rate of "global warming" predicted by the greenhouse theorists.
In an earlier study, DeGaetano pointed out that establishing temperature trends over the past century was very difficult using surface readings because of the many variations from site to site in how those temperatures are taken. Imagine the inconsistencies in the developing world, where volunteers still take many readings.
Weather balloons have shown no warming for the past 45 years. Satellites have shown no warming for the past 23 years. Both methods are infinitely more reliable than surface temperature readings. Yet we are about to radically reorder the culture and economies of the developed world based on the heat island-influenced, error-prone, inconsistent surface readings alone.
Columnist, Edmonton Journal
Editorial Board Member, National Post