What they do is remove old data as they add new data.
Dear Monte,
This is also incorrect. Again, the raw data is still there. And has been, continuously. A history of the data release was written up by New Scientist in 2011.
OK, climate sceptics: here’s the raw data you wanted
Anyone
can now view for themselves the raw data that was at the centre of last year’s
“climategate” scandal.
Temperature records going back 150 years from 5113 weather stations around the world were yesterday released to the public by the Climatic Research Unit (CRU) at the University of East Anglia in Norwich, UK. The only records missing are from 19 stations in Poland, which refused to allow them to be made public.
[links included from original]
Error-correction procedures are used to process the temperature data because of known historical, systemic biases, the greatest of which is the TOBS adjustment, which primarily affected US land surface temperatures. The US historically had a more frontier attitude toward temperature stations, most being voluntary and citizen-manned and monitored, at a time of day most convenient to the station keepers, rather than the science.
Historically, too many stations collected their data in the mid-afternoon, recording the high-low thermometers and then shaking them down. This method successfully captured the day’s high reading, but only if the day had warmed up above the temperature of the previous mid-afternoon, when the thermometer was last shaken down. Otherwise, the day’s actual high was lost, and the higher value from the previous day took its place in the records.
The net result, historically, was average temperature data recorded as higher than the actual.
Statistical methods were used to determine how often this occurred, and by how much the individual station’s values were affected, leading to a correction for this Time of Observation (TOBS) bias. TOBS is no longer needed, except for this historical data. Reporting standards have been raised in the succeeding decades and additional stations created, allowing for more precise modeling of smaller regions, and also allowing for additional error correction.
Most of today’s error correction is due to instruments going bad, and this also occurs far less often due to improvements in the thermometers. Record keeping has also improved. As an example, historically, if a plot of land was repurposed and its weather station moved, the move didn’t always show up in the station’s records. By taking data from nearby stations into account, it’s possible to spot these moves as well.
Every high school student knows they must list potential sources of error at the end of any lab report. Error detection and correction is always on the mind of any researcher, and their standards are enough higher than those of high school students that it’s unlikely any non-specialist is likely to spot an issue they’ve missed.
As ever, Jesse