cc: Susan Solomon , Kevin Trenberth , Matilde Rusticucci , Phil Jones , Brian Hoskins , Peter Lemke , Jurgen Willebrand , Nathan Bindoff , zhenlin chen , Melinda Marquis date: Tue, 09 Jan 2007 16:00:36 +0000 from: Brian Hoskins subject: Re: IPCC WG1 Observations Conference Call to: Martin.Manning@noaa.gov Dear All I kept quiet over the discussion about trend lines as I think the final result of not putting them on the 3 curves in the SPM is the right one. However I certainly defend the use of the 25, 50,100, 150 year trend lines on the temperature curve as in the TS and Chapter 3 as being better than the alternatives. A linear fit may not be a good one but when one is trying to make the smallest number of assumptions it is more defensible than for example putting in seemingly arbitrary break-points. The picture also gives a visual impression of how representative the average rates of change numbers are.The fact that the trend lines for different time-wondows are all different itself shows that the linear fit is not good for the longer time-scales. The monotonically increasing slopes as one moves from the longer to the shorter time-scales is a strong indication of acceleration, but I would not put this in the same sentence as the word "unequivocal". Best wishes Brian