It is always struck me as an amazing irony that the folks at NASA (the GISS is part of NASA) is at the vanguard of defending surface temperature measurement (as embodied in the GISS metric) against measurement by NASA satellites in space.
For decades now, the GISS surface temperature metric has diverged from satellite measurement, showing much more warming than have the satellites. Many have argued that this divergence is in large part due to poor siting of measurement sites, making them subject to urban heat island biases. I also pointed out a while back that much of the divergence occurs in areas like Africa and Antarctica where surface measurement coverage is quite poor compared to satellite coverage.
Anthony Watt had an interesting post where he pointed out that
This means that all of the US temperatures – including those for Alaska and Hawaii – were collected from either an airport (the bulk of the data) or an urban location
I will remind you that my son’s urban heat island project (which got similar results as the “professionals”) showed a 10F heat island over Phoenix, centered approximately on the Phoenix airport. And don’t forget the ability of scientists to create warming through measurement adjustments in the computer, a practice on which Anthony has an update (and here).