In this essay, we summarise the results of our “Has poor station quality biased U.S. temperature trend estimates?” paper, which we have submitted for peer review at the Open Peer Review Journal. The recent Surface Stations project has revealed that about 70% of the U.S. stations used for studying temperature trends are currently located near artificial heating sources, e.g., concrete surfaces, air conditioning units, parking lots. We found that this poor station quality has increased the mean temperature trends of the raw records by about half.
It has previously been claimed that these biases have been removed by a series of data adjustments carried out by the National Climatic Data Center on these station records. However, we found that these adjustments to be inappropriate. The adjustments spread the biases uniformly amongst the stations, instead of removing them.
It appears that poor siting has led to an overestimation of U.S. temperature trends. It is likely that similar siting problems exist for the rest of the world. This means that the amount of “global warming” which is thought to have occurred since the 19th century has probably been overestimated.