Guest essay by Tony Brown
Some readers might recall my recent article ‘The Long Slow Thaw?’
In this I reconstructed Central England temperature to 1538 from its current instrumental date of 1659.
I was surprised by two notable periods of warmth around 1630 and 1530. I am indebted amongst other material, to Phil Jones excellent book ‘Climate since 1500 AD’ plus such books as Le Roy Laduries’ Times of feast times of famine’ which confirm that these were indeed warm periods.
The graph below is from my article but to it has been added the official co2 levels. CET is seen by many scientists as a reasonable but by no means perfect proxy for Northern Hemisphere and Global temperatures.
Please note that the graphing package somewhat inflates the warmth in the decade around 1540, although my recent research- which will extend CET to 1498-demonstrates that the period 1500 to 1540 does indeed appear to be around as warm as the warm period in the recent CET period ending around the year 2000, characterised by the distinct hump.
Also from a graphing viewpoint it is debatable as to where the CO2 line should be placed. I chose to place it around the black trend line as the CO2 and temperature trend line probably needs to start together at the same place. This also provides clarity and context to the graphic although others might feel the CO2 line should be placed elsewhere.
However these are all nuances and the point I want to put over is that temperature is highly variable throughout the CET record -which is at variance to Dr Mann’s (global) work and the assertions of the Met office. This is despite a constant level of co2 until around 1900. The temperature decline since 2000 as the CO2 line rises ever further is especially intriguing.
Does it demonstrate that once you get to around the 300ppm level that the law of diminishing returns sets in as the logarithmic curve of CO2 versus temperatures takes effect? Does it illustrate nothing and the current downward CET slope is merely a blip that will increase sharply again as more CO2 is added?
The apparent effects of adding additional CO2 was clearly shown in an article by David Archibald several years ago,
I merely present my research and findings for comment. An apparent decline perhaps as the logarithmic effect ceases to have any real world meaning? Or merely a hiatus in the ever upwards rise of temperatures since the start of the record in 1659 which may or may not be affected by CO2 and radiative physics?