What corrections are needed to remove known biases in the individual data?
Existing data have well documented biases in them. The most important bias globally was the modification in measured sea surface temperatures associated with the change from ships throwing a bucket over the side, bringing some ocean water on deck, and putting a thermometer in it, to reading the thermometer in the engine coolant water intake. The bucket readings used early in the record were cooler than engine intake observations so the early data have been adjusted warmer to remove that bias. This makes global temperatures indicate less warming than the raw data. The NOAA Sea Surface Temperature bias-correction method that is applied to the historical data from the 1940’s and earlier is based on a comparison between nighttime marine air temperatures and SSTs from ICOADS.
