A group of scientists known for their skepticism about climate change has reanalysed two centuries' worth of global temperature records. Their study largely confirms previous ones: it finds strong evidence that Earth is getting hotter. "The valid issues raised by climate skeptics, when addressed fully and in detail, do not significantly change the answer," says lead author Richard Muller of the University of California, Berkeley. In a testimony (证据) to the US Congress earlier this year, Muller questioned whether global temperature records showed a significant warming during the 20th century. His project, the Berkeley Earth Surface Temperature (BEST), has now pulled together global temperature data going back to 1800 from 15 sources, including data sets held by the World Meteorological Organization and US and UK government agencies. BEST concludes that land temperatures have risen by 1°C since the 1950s. This is largely in line with the three existing global temperature records: GISTEMP, maintained by NASA, the US National Oceanic and Atmospheric Administration's GHCN and HadCRU, kept by the UK Met Office. The 1°C of warming reflects warming above land masses only, so it is not yet a truly global estimate. In a series of papers that have not yet been estimated but are available on the BEST website, the researchers examine how reliable the temperature data is. Contrary to earlier studies that are often quoted by climate skeptics, the BEST researchers find that including data from weather stations in cities—which are warmer than rural areas—makes little difference to the overall trend. "Urban warming doesn't unduly (过分地) bias estimates of recent global temperature change," they say. Blogger Anthony Watts of Watts Up With That has repeatedly claimed that temperature data is unreliable because weather stations are poorly placed—for instance, next to air-conditioning vents or other heat sources. However, BEST finds no statistically significant difference in the trends seen at well-placed and poorly placed stations.