By JR on Thursday, October 20, 2011
A neat and unsurprising demolition of a straw man. The original academic journal article is here. It's just another modelling exercise by the energetic Mark Z. Jacobson. I wonder how he will feel when he realizes that his hundreds of papers were all based on a false premise (AGW)? He is relatively young so he will most probably live to see that day.
Anyway, the conclusions of this paper are undoubtedly correct, if trivial. Less than 1% of the earth's surface is covered by cities so their overall heat contribution has to be minor. What Jacobson overlooks is the reality not captured by the models: The reality that the locations of temperature monitoring stations are far closer to urban heat sources than is allowed for in the official statistics. Hansen apparently makes some such allowances but he keeps secret the details so we can assume that the adjustments are poorly done if not fraudulent.
Urban expansion means that urban heat is captured much more in actual temperature measurements than it would be in a ideal world. Jacobson deals with the ideal rather than the real. Because of the peri-urban location of many temperature-measuring stations, urban heat is almost certainly much larger in its influence on the statistics than it should be and the tiny increment (measured in tenths of a degree) in global temperature over the last century or so could be entirely due to the steady encroachment of urban areas into what were once rural locations
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."