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Politics : Politics of Energy -- Ignore unavailable to you. Want to Upgrade?

To: TimF who wrote (74530)	1/30/2017 8:59:28 AM
From: Alastair McIntosh	Respond to of 86356

But there isn't any good reason for the differences between the raw and adjusted temperatures to be higher now. They aren't. See the right hand graph "U.S. Temperatures 5-year smooth". The fact that around 1910 there is almost no difference between the raw and adjusted temperatures indicates very little adjustment. No, it doesn't. Its just the way it is plotted. The graph you provided showed adjustments relative to the 1900 - 1920 baseline. NCDC takes current temps to be correct and revises previous temps relative to current temps. As the discussion under the graph "U.S. Temperatures 5-year smooth" explains, either current temps or temps at some prior point in time can be assumed to be correct for trend calculations. However, since current readings are assumed to be accurate, a graph based on that assumption will show lower previous temperatures relative to the raw data. see: judithcurry.com NCDC assumes that the current set of instruments recording temperature is accurate, so any time of observation changes or PHA-adjustments are done relative to current temperatures. Because breakpoints are detected through pair-wise comparisons, new data coming in may slightly change the magnitude of recent adjustments by providing a more comprehensive difference series between neighboring stations. When breakpoints are removed, the entire record prior to the breakpoint is adjusted up or down depending on the size and direction of the breakpoint. This means that slight modifications of recent breakpoints will impact all past temperatures at the station in question though a constant offset. The alternative to this would be to assume that the original data is accurate, and adjusted any new data relative to the old data (e.g. adjust everything in front of breakpoints rather than behind them). From the perspective of calculating trends over time, these two approaches are identical, and its not clear that there is necessarily a preferred option.