Cities, Agriculture Heat Things Up
Sprawling cites and agricultural practices are contributing to global warming. Revised calculations in Nature magazine suggest that land-use changes are causing the Earth’s surface temperature to rise by about 0.27 oC per century.
Cities tend to be warmer than nearby rural areas because buildings absorb and retain heat. This ‘urban heat island’ effect means that temperatures are higher at urban monitoring stations than rural ones.
Agriculture can introduce biases too, such as when irrigation increases heat retention in soil.
Eugenia Kalnay and Ming Cai estimated the impact of these land-use effects over the past 50 years by comparing US temperature measurements at surface stations with those measured by satellites and weather balloons, which are far enough above the land surface to escape the biases.
A less prominent climate change that has been detected is a decline in the differences between maximum surface temperatures during the day and minimum temperatures at night. The researchers conclude that half of this observed effect is caused by changes in land use.