Cities' role in global warming said minor

PALO ALTO, Calif., Oct. 19 (UPI) -- Cities put more heat into the atmosphere than rural areas but U.S. researchers say it's modest compared with what greenhouse gases contribute to global warming.

"Between 2 percent and 4 percent of the gross global warming since the Industrial Revolution may be due to urban heat islands," Mark Z. Jacobson, Stanford University professor of civil and environmental engineering, said.

Greenhouse gas contributes about 79 percent to gross warming and black soot from burning fossil fuels accounts for about 18 percent of, a Stanford release said Wednesday.

Some global warming skeptics have argued the urban heat island effect is so strong it has been skewing temperature measurements that suggest global warming is happening.

Jacobson and his colleagues dispute this.

"This study shows that the urban heat island effect is a relatively minor contributor to warming, contrary to what climate skeptics have claimed," Jacobson said. "Greenhouse gases and particulate black carbon cause far more warming."