"Land-based temperature readings are corrupted by the urban heat island effect," he says. "Urban areas encroaching on thermometer stations warm the micro-climate around the thermometer due to vegetation changes, concrete, cars and houses."
As such, he alleges that the GISS figures - which are enormously influential in the climate change debate - are "hopelessly corrupted" and may even be manipulated to suit Hansen's views on global warming.
A group of weather buffs in the US also has attacked GISS's methodology, putting together an online photo gallery of US weather stations at website www.surfacestations.org that shows some thermometers situated next to asphalt runways and parking lots where they would pick up excess warming.
But GISS says the distorting impact of this urban warming is negated because data from these stations is modified to remove these effects and give a true reading. Hansen acknowledges there may be flaws in the weather station data because temperature measurement is not always a precise science. But he says this does not mean big-picture trends can't be drawn from the data.
He says: "That doesn't mean you give up on the science and that you can't draw valid conclusions about the nature of earth's temperature change."Then in discussing the GISS Y2K correction it says merely before quoting Rush Limbaugh:
Hansen has been infuriated by the attacks on GISS by climate change critics. Last year Canadian blogger and retired businessman Stephen McIntyre exposed a minor mistake in Hansen's figures that had caused GISS to overstate US temperatures by a statistically small 0.15C since 2000.The point is not the overstatement directly but the fact that this overstatement meant that the "hottest year" leader board now became heavily dominated by the 1930s instead of 1998-2006. In other words contrary to various greenshirt screaming US temepratures are essentially unchanged over a 70+ year cycle (see below for more). Given that, as the article notes elsewhere, atmospheric CO2 levels have risen significantly during this period this looks like evidence against the CO2 causes global warming argument.