As has been stated before, the surface stations used to collect temperature data MUST be repaired and re-located!!
Per Douglas V. Hoyt, et al:
UHI have significant impacts of measured trends. It is likely a large fraction of the 0.6 C warming reported for the 20th century is caused by spurious non-climatic effects such as UHIs. If 0.10 C/decade represents the warming in the central portions of towns and cities, as both pro and con arguments suggest, then it is reasonable to assume most temperature measurements are away from the center, so the UHI trends might be a quarter or a half of the central cities or 0.025 C to 0.05 C/decade. Kalnay suggests it is 0.027 C/decade over the US and this probably the most reliable number we have so far. That would mean about 45% of the observed warming is actually spurious urban warming.
Douglas V. Hoyt is a solar physicist and climatologist who worked for more than thirty years as a research scientist in the field. He has worked at NOAA, NCAR, Sacramento Peak Observatory, the World Radiation Center, Research and Data Systems, and Raytheon where was a Senior Scientist. He has conducted research on issues related to climate change, changes in solar irradiance on all time scales, and the sun-climate connection. His most recent publication is the book "The Role of the Sun in Climate Change" . He has published nearly 100 scientific papers on solar irradiance variations, the greenhouse effect, atmospheric transmission, aerosols, cloud cover, sunshine, radiative transfer, radiometers, solar activity, sunspot structure, sunspot decay rates, and the history of solar observations.
He has received no funding from any fossil fuel entity or government entity. His work is influenced only by the data and the study of the scientific literature.
http://www.warwickhughes.com/hoyt/climate-change.htm
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