- ITHACA, N.Y. -- If you think
that summers are getting hotter, you could be right -- depending on where
you live. Summers are heating up if you live in or near any major U.S.
city. But in rural areas, temperatures have remained relatively constant.
-
- "What surprised me was the difference in the extreme
temperature trends between rural and urban areas," says Arthur T.
DeGaetano, Cornell associate professor of earth and atmospheric sciences,
who 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. "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."
-
- Because of population growth in urban and suburban areas
over the past four decades, particularly in major East Coast cities, there
are more hot summer nights than ever, says DeGaetano. "This means
that cities and the suburbs may be contributing greatly to their own heat
problems," he says. "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."
-
- Working with Robert J. Allen, a researcher in earth and
atmospheric sciences, he 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.
-
- The growth was the lowest in the central United States,
with only two more very warm nights. West of the Rocky Mountains the increase
has been about five nights. DeGaetano explains this disparity by the fact
that there are simply fewer urban areas in these regions.
-
- DeGaetano classifies a warm night as 70 degrees Fahrenheit
in the Eastern, Southern and Midwestern United States. In the Southwest,
he says, 80 degrees would be considered a warm night and 70 degrees would
be considered cool.
-
- The 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 a forthcomingJournal of Climate . It was supported by grants
from NASA and from the National Oceanic and Atmospheric Administration.
-
- 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 says that the decade of the
1960s stands out as a transition between a period that was relatively 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,"
he explains.
-
- Climate-reporting stations located in urban areas often
are indicators of the huge growth around them. In Manhattan, for example,
the station is located in Central Park, which was surrounded by a highly
developed urban area even a century ago. Thus that station did not show
the wild fluctuations recorded in cities such as Miami and Los Angeles,
which have grown exponentially over the past 100 years.
-
- In very warm periods throughout the past century, drought
has been a factor. "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. And these peaks tend to coincide with widespread drought,"
says DeGaetano.
-
-
-
- Editor's Note: The original news release can be found
at http://www.news.cornell.edu/releases/Sept02/HotterSummers.bpf.html
-
- Note: This story has been adapted from a news release
issued by Cornell University for journalists and other members of the public.
If you wish to quote from any part of this story, please credit Cornell
University as the original source. You may also wish to include the following
link in any citation:
-
- http://www.sciencedaily.com/releases/2002/09/020930075212.htm
- Copyright © 1995-2002 ScienceDaily Magazine
|