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Urban Warming in China
Reference
Weng, Q. 2001. A remote sensing-GIS evaluation of urban expansion and its impact on surface temperature in the Zhujiang Delta, China. International Journal of Remote Sensing 22: 1999-2014.

What was done
Covering an area of 17,200 square kilometers, the Zhujiang Delta (located between 2140'N and 23N, and 112E and 113 20'E) is the third largest river delta in China. It has experienced rapid urban development since economic reforms were instituted there in 1978. In an effort to evaluate the effect of land use/land cover changes on surface temperatures in this region, the author conducted a series of analyses on remotely-sensed Landsat Thematic Mapper data in a Geographic Information System (GIS).

What was learned
Considerable changes in land use were noted between 1989 and 1997. The total area associated with cropland declined by nearly 50 percent during this time period, while the area of urban or built-up land increased by nearly the same percentage. Upon normalizing the surface radiant temperature for each year (1989 and 1997), the author utilized the GIS technique of image differencing to produce a radiant temperature change image that was subsequently overlaid in the GIS with images of urban expansion. The results indicated that "urban development between 1989 and 1997 has given rise to an average increase of 13.01K in surface radiant temperature."

What it means
It is highly probable that the urban-induced surface radiant temperature increase of 13C per decade calculated for the Zhujiang Delta of China has introduced an urban warming bias in the near-surface air temperature records of weather stations located there. Removing and/or filtering out such biases in temperature series remain a daunting task for researchers examining global climate change. This challenging work must be done, however, before any change in air temperature can be ascribed to CO2-induced global warming.