8 ms·

Roy aligned the trends to match at the very beginning of the satellite record to make it more obvious how the trends tend to diverge over time. Aligning with th

by glenra 12y ago

Roy aligned the trends to match at the very beginning of the satellite record to make it more obvious how the trends tend to diverge over time. Aligning with the MIDDLE of the record somewhat obscures the fact that his chart was meant to show, but even your "properly aligned" chart still shows recent measurements falling well below prediction.

anon1385 12y ago
That is not how to use temperature anomalies. The entire point of using anomalies rather than the raw data is to get around the fact that the various data sets are not calibrated against each other. Picking a broad baseline avoids having to worry about distortion in the graph due to the arbitrary starting point. The individual records will be different for any given year, because of error and because they are not always measuring the same thing anyway (HADCRUT4 is surface temperature, UAH is troposphere). The fact that the CMIP5 mean and UAH have nearly the same anomaly value in 1983 when using a 1979-1983 baseline is just coincidental. They diverge quite a bit in several of the other years in the 1979-83 period. Roy crops his graph to hide that and make it look like they begin together. So he hasn't even done what you claim (aligned the trends to match at the very beginning of the satellite record) because his method puts the CMIP5 mean anomaly about 0.2 of a degree above UAH at the beginning of the satellite record. Plotting all the available data would show that. Hiding data just deceives the reader. If he really wanted to just "match at the very beginning of the satellite record" as you suggest, why not just use a baseline of 1979? I suspect the answer to that is that it wouldn't support his argument to present the data that way. Your idea of aligning to the beginning of the satellite record is ill conceived anyway. That would only make sense if GCMs took the temperature data at that time as their starting point. They don't.

by glenra 12y ago

anon1385 12y ago

That is not how to use temperature anomalies. The entire point of using anomalies rather than the raw data is to get around the fact that the various data sets are not calibrated against each other. Picking a broad baseline avoids having to worry about distortion in the graph due to the arbitrary starting point. The individual records will be different for any given year, because of error and because they are not always measuring the same thing anyway (HADCRUT4 is surface temperature, UAH is troposphere). The fact that the CMIP5 mean and UAH have nearly the same anomaly value in 1983 when using a 1979-1983 baseline is just coincidental. They diverge quite a bit in several of the other years in the 1979-83 period. Roy crops his graph to hide that and make it look like they begin together. So he hasn't even done what you claim (aligned the trends to match at the very beginning of the satellite record) because his method puts the CMIP5 mean anomaly about 0.2 of a degree above UAH at the beginning of the satellite record. Plotting all the available data would show that. Hiding data just deceives the reader. If he really wanted to just "match at the very beginning of the satellite record" as you suggest, why not just use a baseline of 1979? I suspect the answer to that is that it wouldn't support his argument to present the data that way. Your idea of aligning to the beginning of the satellite record is ill conceived anyway. That would only make sense if GCMs took the temperature data at that time as their starting point. They don't.