When is a Trend and Trend?

Answer:  When it is too late to matter.

Updated Stuff Below:

I can go on about the need to consider baselines until I am blue in the face and it won't matter, people will "see" what they wish to "see".  The average AGW fan will "see" the increased slope in the data following an unexpetced downturn and "see" a signature of Antropogenic Global Warming.  

With a little curiosity, the AWG fan might look at some other data, like say,

this plot that has a double dip ENSO oscillation, followed by an increasing warm ENSO trend culminating in a OMG what happened! event.  Obviously, the Clinton Administration was asleep at the switch because everything boils down to politics.

The 1S 91W is west of South America near the Galapagos Islands.  Tmin from the Best data set was used since being measured on islands, the minimum temperature would be pretty close to the sea surface temperature.  Near the Galapagos Islands, Tmin has bee increasing with a long term trend of about 0.02C per year, 0.2C per decade, 2.0C per century for about a century.  Probably due to the heavy duty Ecuadorian industrial complex.  Yes, that was a joke.

Then again, it could be because the Tropical Eastern Pacific wanders up and down a few degrees all the time, on occasion with a little spike above or below that range.  Generally, those spikes means something is changing.  About 125 thousand years ago, there was a little off the chart spike.  Might be time for another spike.  1998 might have been that spike.  So what happened after the spike about 125 thousand years ago? Not much.

Even though the time scale of this paleo reconstruction by Hebert et al. is a touch longer than decadal, the settling or decay curve following the 1998 spike will likely be somewhat similar, but never exactly the same.

So a trend is not all that helpful, but a pattern, even though not perfectly repeating, can be useful.

The new stuff:

Someone just could not believe their eyes when I showed them the Galapagos Tmin data stating that it makes a PDG ENSO tracker.  Imagine that?

So here is the BEST Tmin for the Galapagos Islands area with McGregor et al. Unified ENSO Proxy Reconstruction.  Just to make sure:


WDC PALEO CONTRIBUTION SERIES CITATION: 
McGregor, S., et al. 2010. 
350 Year Unified ENSO Proxy Reconstruction. 
IGBP PAGES/World Data Center for Paleoclimatology 
Data Contribution Series # 2010-015. 
NOAA/NCDC Paleoclimatology Program, Boulder CO, USA.
www.clim-past.net/6/1/2010/

Now I did not detrend the BEST Galapagos Island Tmin since the trend or lack there of was the point.  ENSO may be considered a neutral oscillation but what oscillates ENSO doesn't have to be trendless.  The +/- 1C variation is "normal" and the excursions beyond +/- 1C would be the abnormal events likely associated with shifts some nature around that general time.  Had I detrended, the "fit" would have been more impressive.