Hot Times in the City Getting Hotter

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Hot Times in the City Getting Hotter

ITHACA, New York, September 27, 2002 (ENS) - U.S. cities have 10 more hot

nights a year than 40 years ago, Cornell University climate researchers have

discovered. But while summers are heating up in urban areas, in rural

areas, temperatures have remained more constant, said Arthur DeGaetano, a

Cornell associate professor of earth and atmospheric sciences. DeGaetano

reviewed temperature trends from climate reporting stations across the

United States over the past century and examined data from the last 40 years

in greater detail.

" What surprised me was the difference in the extreme temperature trends

between rural and urban areas, " said DeGaetano. " I expected maybe a 25

percent increase for the urban areas compared to the rural ones. I didn't

expect a 300 percent increase across the U.S. "

Working with , a researcher in earth and atmospheric sciences,

DeGaetano found that urban areas across the United States now have an

average of 10 more very warm nights a year than they did 40 years ago. In

rural areas there was an average increase of only three warm nights a year

in the same period.

" This means that cities and the suburbs may be contributing greatly to their

own heat problems, " he said. " Greenhouse gases could be a factor, but not

the one and only cause. There is natural climate variability, and you tend

to see higher temperatures during periods of drought. "

DeGaetano classified a warm night as 70 degrees Fahrenheit in the eastern,

southern and midwestern United States. In the southwest, he said, 80 degrees

would be considered a warm night and 70 degrees would be considered cool.

Since the beginning of the 20th century almost three-fourths of the climate

reporting stations examined in the study have shown an increase in the

number of very warm nights. DeGaetano said that the decade of the 1960s

stands out as a transition between a period that was stable and cool, and

the sharp increase in warm nights that has occurred in recent decades.

" You would not expect such a change in the number of very warm nights to

occur by chance. We saw a statistically significant shift, " DeGaetano said.

In very warm periods throughout the past century, drought has been a factor

in temperature fluctuations.

" Warm temperature trends in the past century across the United States are

strongly influenced by the peaks in warm maximum and warm minimum

temperature extremes during the 1930s and to some extent the 1950s, " said

DeGaetano. " These peaks tend to coincide with widespread drought. "

The Cornell research article, " Trends in Twentieth-Century Temperature

Extremes in the United States, " describes average temperature increases for

all cities and rural areas across the United States. It will be published in

an upcoming issue of the " Journal of Climate. "

Copyright Environment News Service (ENS) 2002.