The US temperature data. Thanks to Joe Bastardi's twitter stream for this one, and feel free to go to his site for all kids of weather data.
From the report:
"During the past few years I recruited a team of more than 650 volunteers to visually inspect and photographically document more than 860 of these temperature stations. We were shocked by what we found.
We found stations located next to the exhaust fans of air conditioning units, surrounded by asphalt parking lots and roads, on blistering-hot rooftops, and near sidewalks and buildings that absorb and radiate heat. We found 68 stations located at wastewater treatment plants, where the process of waste digestion causes temperatures to be higher than in surrounding areas.
In fact, we found that 89 percent of the stations – nearly 9 of every 10 – fail to meet the National Weather Service’s own siting requirements that stations must be 30 meters (about 100 feet) or more away from an artificial heating or radiating/reflecting heat source.
In other words, 9 of every 10 stations are likely reporting higher or rising temperatures because they are badly sited.
It gets worse. We observed that changes in the technology of temperature stations over time also has caused them to report a false warming trend. We found major gaps in the data record that were filled in with data from nearby sites, a practice that propagates and compounds errors. We found that adjustments to the data by both NOAA and another government agency, NASA, cause recent temperatures to look even higher.
The conclusion is inescapable: The U.S. temperature record is unreliable."