The longest complete temperature series in the world is that of Berlin which began in 1701*. The chart reveals that in that time the linear trend has shown a warming trend of +0.05°C per decade. That doesn’t sound much but in a 318 year series that adds up to mean temperature being 1.4°C higher than it was in 1701. If you examine the linear trend since 1965, that reveals a decadal warming of +0.31°C, or if you prefer a rise of 3.1°C in 100 years which definitely sounds a little more alarming.
In the UK the longest series available in the CRUTEM mean temperature data from the Met Office is surprisingly Leuchars in Scotland, the monthly series of which started in 1800, and as far as I can see is complete. The long term warming trend since 1800 is identical to that of Berlin, but the warming trend since 1965 is a little more modest at +0.23°C per decade. This might be due to the maritime influence that affect Leuchars.
The trend is not the same across all parts of the world, for instance in Brisbane Australia although the long term trend (on a much shorter series that started in 1887) is +0.07°C, the trend since 1965 is only just a little higher at +0.12°C per decade. Again Brisbane is a coastal site which might temper that trend.
Wander a little further east into Europe than Berlin, and another long temperature series, that of St Petersburg series which started in 1743 shows a warming trend since 1965 that’s even higher than Berlin’s at +0.46°C per decade since 1965.
Finally, because I don’t want to completely knock you sideways with far too many graphs, here’s a look at one final graph for Svalbard in the Arctic Ocean. This is probably one of the most extreme warming trends that you will find on the planet, with a warming trend of +1.03°C, that’s not for 100 years that’s per decade! As far as I can see the mean temperature at Svalbard as risen from -8.0°C to -2.4°C since 1965.
How much store you can place in a 54 year linear trend on temperature data that is non-linear and as volatile as mean annual temperatures is debatable. What I do think the graphs show are the facts of the matter and simply can’t be ignored. What we can do about it of course is another matter entirely, all I do know is if warming continues at the same rate that it is, the globe will see the rise to +1.5°C above pre-industrial times by 2034 rather than 2044.
As an aside, the application I developed to visualise the CRUTEM temperature data and produce these graphs is one of the best and most useful climate programs I have written.
The application does require a lot of data, 132 MB to be exact from over 7,000 stations across the world, and for the life of me I can’t understand why the Met Office fails to include the three stations that make up the CET series. And where too is the Oxford temperature series that started in 1813 and is purportedly to be the longest series in the British Isles? After all this monthly temperature data is used by the Met Office to estimate global temperature and its inclusion would be obvious.