The officially published global temperature records all converge on a total temperature rise since the late 19th century of about 0.9 (0.8–1.0) degrees Celsius:
But to what extent can we be confident that this is how the ‘global average surface temperature’ (GAST) anomaly actually evolved over this time frame?
The truth is: We can’t. At all.
This is fundamentally a matter of data coverage, but – just as importantly – it is also a matter of methodology. How do you make up for a paucity of data? How do you properly compile, weight and interpolate data into a reliable “global average” when that data – the actual observational information that you have collected and thus have at your disposal – provides nothing like a full global coverage? And how do you make this “global average” of yours consistent over time when your data coverage (both in total and in spatial distribution) vastly changes over that same time frame? What basic assumptions will you have to rely on? Because, make no mistake, an interpretive undertaking such as this will crucially have to rest on a foundation of some rather sweeping presuppositions. Continue reading →
In July I wrote a blog post where a strange and very conspicuous step change indeed in global mean temps relative to the trended AMO (North Atlantic SSTa), occurring across the 8-year period of 1963-70, was pointed out:
As you can clearly see, the two curves generally follow each other in remarkable style all the way from 1860 till today, except for the relatively sudden and substantial global upward shift taking place across the last half of the 60s, being firmly established by the end of 1970. After this point, the curves are back to tracking each other to an equally impressive degree as before the shift, only now with the global raised 0.25 degrees above the North Atlantic.
Something that’s been on my mind for a while is that strange relationship – or, to be more precise, that conspicuous correlative relationship – between the evolution of North Atlantic (70N-0, 80W-0) SST anomalies (the AMO, only with trend included) and the global temperature anomalies:
Figure 1. Annual AMO (with trend imposed) vs. global temps (HadCRUt4, adjusted down 0.064 degrees post 1998) from 1860 to 2014.Continue reading →