Guest essay by Neil Catto
The CET record started in 1659 close to the minimum of the little ice age. As such, it is with no surprise that last year (2014) was the warmest on record. It would appear to be a natural recovery. The monthly mean temperature of 8.87 Deg C in 1659 has increased to 10.95 Deg C in 2014; which equates to 0.06 Deg C/decade.
I used the CET mean monthly data 1659-2014: Downloaded 6th Jan 2015 http://www.metoffice.gov.uk/hadobs/hadcet/data/download.html
My main interest in this data set is to gain better understanding between natural variation and AGW. I consider the CET as a reasonable representation of Northern Hemisphere trends. In 1739 Mount Tarumae in Japan erupted with a VEI force 5. The mean monthly CET temperature in 1739 was 9.21 Deg C, in 1740 there was a significant drop to 6.84 Deg C à and in 1741 a recovery to 9.32 Deg C. This natural occurrence had the equivalent drop in temperature of -23.5 Deg C/decade and recovery of 24.6 Deg C/decade. With a natural variation of this magnitude I never understand the alarm about 2.0 deg C/decade, human life survived and exponentially grew in numbers.
The last time I downloaded CET data was 22nd May 2013. Out of interest I thought I would compare the two data sets. The results were interesting to say the least.
Fig 1 anomalies between CET downloaded in May 2013 with CET downloaded in Jan 2015 (data to Dec 2014)
It is noticeable that nearly every adjustment is positive, with no negative changes. The whole data set shows an average increase of 0.03 Deg C in 20 months or equivalent to 0.18 Deg C/decade.
What is the reason for these data adjustments?
How often and by how much are these data adjusted?
Is this anthropogenic warming caused by man-made adjustments?