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 →
Ten days ago, Nick Stokes wrote a post on his “moyhu” blog where he – in his regular, guileful manner – tries his best to distract from the pretty obvious fact (pointed out in this recent post of mine) that GISS poleward of ~55 degrees of latitude, most notably in the Arctic, basically use land data only, effectively rendering their “GISTEMP LOTI global mean” product a bogus record of actual global surface temps.
Among other things, he says:
“The SST products OI V2 and ERSST, used by GISS then and now, adopted the somewhat annoying custom of entering the SST under sea ice as -1.8°C. They did this right up to the North Pole. But the N Pole does not have a climate at a steady -1.8°C. GISS treats this -1.8 as NA data and uses alternative, land-based measure. It’s true that the extrapolation required can be over long distances. But there is a basis for it – using -1.8 for climate has none, and is clearly wrong.
So is GISS “deleting data”? Of course not. No-one actually measured -1.8°C there. It is the standard freezing point of sea water. I guess that is data in a way, but it isn’t SST data measured for the Arctic Sea.”
The -1.8°C averaging bit is actually a fair and interesting point in itself, but this is what Stokes does; he finds a peripheral detail somehow related to the actual argument being made and proceeds to misrepresent its significance in an attempt to divert people’s attention from the real issue at hand. The real issue in this case of course being GISS’s (bad) habit of smearing anomaly values from a small collection of land data points all across the vast polar cap regions, over wide tracts of land (where for the main part we don’t have any data), over expansive stretches of ocean (where we do have SST data readily available) AND over complex regions affected by sea ice (where we indeed do have data (SSTs, once again) when and where there isn’t any sea ice cover, but none whatsoever when there is), all the way down to 55-60 degrees of latitude. Continue reading →
Two renditions of global surface (land+ocean) temperature anomaly evolution since 1970:
The upper red curve represents the final 46 years of the temperature record most frequently presented to (and therefore most often seen by) the general public: NASA’s official “GISTEMP LOTI global mean” product. There is hardly any “pause” in ‘global warming’ post 1997 to be spotted in this particular time series. It is the one predictably trotted out whenever an AGW ‘doom and gloom’ activist sees the need to ‘prove’ to a sceptic that “global warming” indeed continues unabatedly and rub his face in it.
The lower curve in Fig. 1 is an altogether unofficial one. However, it should still be fairly familiar to most. It is the one having been consistently used by me on this blog to represent actual global surface temperature anomalies since ~1970. It is time to explain (and to show) why …
This particular curve is simply the now defunct UEA/UKMO land+ocean product “HadCRUt3 gl” with an en bloc downward adjustment of 0.064 degrees included from January 1998*. The “Pause” is here vividly seen as but one (albeit an extended one) of several plateaus in an upward, distinctly steplike progression of global temps since the 70s.
*I discussed here why this is a necessary adjustment.
Now, which one of these two renditions is more honest in its attempt to depict the actual “reality” of things? And which one is the result of simply inventing extra warming?
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 →