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.

Posted in AGW, Climate Change, climate science, CRU | 10 Comments

Some CRU Anomalies

The previous post showed that changes to weather station data between CRUTEM3 and CRUTEM4.6 are responsible for converting the Hiatus into a warming trend. Here I look into some examples of those changes. I first looked for big changes in the monthly ‘normal’ values between 1961 and 1990. This identified some inconsistencies.

WMO identifiers are supposed to be fixed locations but Station 218240 has been changed and moved thousands of miles between CRUTEM3 and CRUTEM4.6. Despite this several temperature measurements remain exactly the same, which is simply impossible!

Same ID but different stations both using exactly the same 3 year temperature record ?

At the other extreme we have stations whose values have changed significantly

Same station but very different monthly temperature and different normals.

136 stations have seasonal monthly normals that have changed by more than 1C between CRUTEM3 and CRUTEM4.6. In some cases eg. Los Angeles, the station has moved in altitude going from downtown to Pasadena. However, others like Miami apparently are the same station but record completely different monthly mean temperatures going from CRUTEM3 to CRUTEM4.

Miami monthly temperatures CUTEM3 compared to CRUTEM4.6

Maybe this is a different station in another location since Miami is flat. However if so then this just demonstrates how great the variability is, even within one city.

What I think this really highlights is the lack of (available) metadata describing CRU station changes and updates, plus at least one data quality control issue. This doesn’t  explain why the post 1998 warming trend changed.


Posted in AGW, Climate Change, CRU | Tagged | 12 Comments

Whatever happened to the Global Warming Hiatus ?

The last IPCC assessment in 2013 showed a clear pause in global warming lasting 16 years from  1998 to 2012 – the notorious hiatus. As a direct consequence of this  AR5 estimates of climate sensitivity were reduced and CMIP5 models appeared to clearly overestimate trends. Following the first release of HadCRUT4 in 2012  the ‘headline’ that followed was that 2005 and 2010 were now marginally warmer than 1998. This was the first dent in removing the hiatus. Since then each new version of H4 has showed further incremental warming trends, such that by 2019 the hiatus has now completely vanished. Anyone mentioning it today is likely to be ridiculed by the climate science community. So how did this reversal happen within just 7 years? I decided to find out exactly why the post 1998 temperature record changed so dramatically in such a short period of time.

In what follows I always use the same algorithm as CRU for the station data and then blend that with the Hadley SST data. I have checked that I can reproduce exactly the latest HadCRUT4.6 results based on the current 7820 stations from CRU merged with  HadSST3. Back in 2012 I downloaded the original station data from CRU –  CRUTEM3. I have also downloaded the latest CRUTEM4 station data.

Figure 1 compares the latest HadCRUT4.6 results with the last version of HadCRUT3.

Figure 1. Comparison of HadCRUT3 and the latest HadCRUT4.6 Notice how all trends pivot around the 1998 El Nino peak.

I had assumed that the reason for the apparent trend change was because CRUTEM4 had added many new weather stations in the Arctic (removing some in S.America as well), while additionally the SST data had also been updated (HadSST2 moved to HADSST3). However, as I show below, my assumption simply isn’t true.

To investigate I recalculated a ‘modern’ version of HadCRUT3 by using only the original 4100 stations (used by CRUTEM3) from CRUTEM4 station data.  The list of these stations are defined here. I then merged these with  both the older HadSST2 and HADSST3 to derive annual global temperature anomalies. Figure 2 shows the result. I get almost exactly the same values as the full 7820 stations in HadCRUT4. It certainly does not reproduce HadCRUT3 !

Figure 2. The black curve is based on “modern” CRUTEM3 stations combined with HADSST3 and the Yellow  curve is “modern” CRUTEM3 stations with HADSST2

This result provides two conclusions.

  1. Modern CRUTEM3 stations give a different result to the original CRUTEM3 stations.
  2. SST data is not responsible  for the difference between HadCRUT4 and HadCRUT3

To confirm point 1) I used exactly the same code to regenerate HadCRUT3 temperature series using the original CRUTEM3 station data as opposed to the ‘modern’ values based on CRUTEM4.

Figure 3: Comparison of HadCRUT3 with my calculation using the original CRUTEM3 station data.

The original CRUTEM3 station data I had previously downloaded in 2012. These are combined with HADSST2 data. Now we see that  the agreement with the H3 annual temperatures is very good, and indeed reproduces the hiatus.

So the conclusion is very simple. The monthly temperature values in over 4000 CRUTEM3 stations have all been continuously changed, and it is these changes alone that have resulted in transforming the 16 year long hiatus in global warming into a rising temperature trend. Furthermore all these updates have only affected temperatures AFTER 1998! Temperatures before 1998 have hardly changed at all, which is the second requirement needed to eliminate the hiatus.

P.S. I am sure there are excellent arguments as to why pair-wise ‘homogenisation’ is wonderful but why then does it only affect data after 1998 ?


Posted in AGW, climate science, IPCC, UK Met Office | 91 Comments