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In urban communities, less than 1 in 100 inhabitants died from Spanish flu in 1918, but in isolated communities up to 9 out of 10 died. An important explanation for the differences is due to different exposure to influenza in the decades before the Spanish flu came. Those living in urban communities probably had a higher degree of pre-existing immunity that protected against illness and death in 1918 than those living in very isolated rural areas. This is shown in a new study from the Norwegian Institute of Public Health.

UC Berkeley physicist Richard Muller and others were looking at the so-called urban heat island effect - the notion that because more urban temperature stations are included in global temperature data sets than are rural ones, the global average temperature was being skewed upward because these sites tend to retain more heat. Hence, global warming trends are exaggerated. Using data from such urban heat islands as Tokyo, they hypothesized, could introduce "a severe warming bias in global averages using urban stations." In fact, the data trend was "opposite in sign to that expected if the urban heat island effect was adding anomalous warming to the record. The small size, and its negative sign, supports the key conclusion of prior groups that urban warming does not unduly bias estimates of recent global temperature change."

In the next 20 years, more than 590,000 square miles of land globally - more than twice the size of Texas - will be gobbled up by cities, a trend that shows no signs of stopping and one that could pose threats on several levels, says a Texas A&M University geographer who is part of a national team studying the problem.