Swanson’s projection for future temperature using presumed regime shifts can be compared with our projection.

The above figure was posted at RealClimate (note this figure is not contained in their paper) with flat temperature intersecting with an extrapolated underlying rate of around 1C/Century seen between 1950 and 1998 at around 2020.

Our projection for temperature, from figure 3 of our paper archived at arXiv and submitted to IJF, Structural break models of climatic regime-shifts: claims and forecasts is based on the current flat rate intersecting with an extrapolated underlying rate of around 0.5C/Century between 1910 and 1976, at around 2050.

Which is more valid? Our reasoning is that if you are to accept that temperatures are being suppressed in a -ve phase of the PDO, then they must have been enhanced in a +ve phase from 1976 to 1998. Therefore, it is invalid to take the underlying rate of warming from 1976 to 1998.

Sure, assuming the higher rate of underlying warming fits the climate models, IPCC and AGW alarmism story better, but I can’t see the logic in it. Note also its inconsistent with the trend line from 1976 in their paper (below) which intersects around year 2000 (compare with first figure above).

Moreover, all of the empirical estimates of climate sensitivity (not the climate model ones) come in at an underlying warming rate closer to 0.5C/century, as the figure below from Roy Spencer illustrates.

Are these inconsistent? Swanson says (inaccurately, its actually from 1950, doh!) of the presumed underlying warming trend:

Also shown is a linear trend using temperatures over the period 1979-1997 (no cherry picking here; pick any trend that doesn’t include the period 1998-2008). We hypothesize that the established pre-1998 trend is the true forced warming signal, and that the climate system effectively overshot this signal in response to the 1997/98 El Niño.

In other words, Swanson isn’t committed. But the figure prepared for the RealClimate post chose a period corresponding the the highest rate of warming, consistent with the climate models, but internally inconsistent with their assumption that the current plateau in temperatures is due to regime shift.

We picked a period corresponding to a consistent view of regime-shifts both enhancing and suppressing the underlying trend, and also consistent with empirical measurements of climate sensitivity.

On the face of it, it looks like logical consistency and empirical evidence, versus agreement with the climate models and damn the logic and evidence – a politically correct projection?