H3-H4 temperature differences

In this post I look at the effect of changes in the original set of CRUTEM3 stations.

Shown below are the spatial changes in temperatures between HadCRUT3 (2013) and the latest HadCRUT4.6 (2019) from 1998 to 2010. These are calculated using just the original set of CRUTEM3 stations and their counterparts in H4. Each annual 5×5 deg. cell is averaged over  12 months.

Fig 1: Map showing the effects of CRU adjustments in station temperature between 1998 & 2010

There is essentially no change in SST between H3 (HadSST2) and H4.6 (HadSST3) so the increased warming trend since AR5 is simply caused by changes to the underlying CRU station data. Most of the significant changes occur in Asia and N. America. Here are the static temperature differences shown on the same scale as the temperature anomalies for 1998 and 2010.

Fig2. Annual temperature anomalies calculated using CRUTEM3 (2013) and HadSST2.

and now 2010.

Fig 3. HadCRUT4.6 calculated using only modern versions of the original CRUTEM3 stations combined with HadSST3.

Finally  I show  the differences between H4 and H3 temperature anomalies plotted  on the same scale. In an idea world this plot should be pale blue with zero difference.

The difference between Figure 4 and Figure 5

The yellow to pink areas are roughly 0.5 to 1.0C warmer than HadCRUT3 , demonstrating how  after 7-years an apparent increase in ~4000 global land temperatures can explain why the AR5 hiatus essentially evaporated.  The original weather station data cannot have changed, so these effects are probably caused by merging of nearby local stations, homogenisation between regional stations, correcting errors, or something else. Probably only Tim Osborne or Phil Jones could explain.

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2 Responses to H3-H4 temperature differences

  1. Olof R says:

    The change from HadSST2 to 3 had an effect on the pause. The “pause” trend 1998-2012 increased by 0.035 C/decade in HadSST 3
    Here is a comparison of old and new HadCRU datasets trends through Wood for Trees:


    The exact calculated trends can be seen if you press “raw data”

    The increase in SST trend is very much what one can expect from the ship/buoy adjustment that was introduced in HadSST3. Buoy data was adjusted up ~0.12 C compared to ship ERI data. The proportion of buoy data increased approximately from 50% in 1998 to 90% in 2012. Thus, the adjustment should increase the temperature by 0.048 over the period. Dividing this by 15 years suggests a trend increase of 0.032 C/decade, which is close enough to the actual 0.035

    The version change in Crutem increased the land trend more, ~ 0.095 C / decade. Despite the fact that land only constitutes 30% of the global surface, the land component must have had a somewhat larger effect on the global trends, compared to that of SST.

  2. A C Osborn says:

    Is not HADCRUT data based on NASA data?
    If so I suggest that you take a look at the analysis carried out by E M Smith on the GCHN data changes between versions.
    They are extremely revealing.

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