Researchers led by the Georgia Institute of Technology report that the mean surface temperature in the region has risen 0.09 degrees Fahrenheit (0.05 degrees Celsius) per decade since 1979. Also, nighttime low temperatures have risen much faster than the daytime high temperatures. The average reduction of the day-to-night temperature range was 0.24 degrees F (0.132 degrees C) per decade.

Their findings will appear in the June 29 print edition of the journal Proceedings of the National Academy of Sciences.

To estimate the temperature changes due to urbanization, researchers used a new approach that integrated meteorological station observations, model-assimilated temperature predictions, satellite-measured greenness and China's census data. The modeling data - provided by the National Oceanic and Atmospheric Administration's Centers for Environmental Prediction and the U.S. Department of Energy - is considered more accurate than previous information because of its improvements in accounting for temperature range differences affected by cloud cover and soil moisture, the researchers note.

"These results are further evidence of the human impact on climate," says lead author Liming Zhou, a Georgia Tech researcher working with Professor Robert Dickinson, a global climate modeler in the Georgia Tech School of Earth and Atmospheric Sciences.

Carbon dioxide from industrial and automobile emissions has been suspected to be the primary force in global warming. Scientists have attributed a 0.9 degrees F (0.5 degrees C) increase in global temperature in the 20th century to a significant atmospheric increase of greenhouse gases, including carbon dioxide. They predict this increase will continue through the 21st century and cause continued increases in extreme weather, rising sea levels, and the retreat of glaciers and polar ice caps.

"Human-induced changes in land use - such as urbanization, deforestation, and agricultural and irrigation practices - can affect local and regional climate and even large-scale atmospheric circulations," Zhou explains. "They may have changed climate as much as greenhouse gases over some particular regions of land."