With regard to global temperature the IPCCIPCC The Intergovernmental Panel on Climate Change is an intergovernmental body of the United Nations responsible for advancing knowledge on human-induced climate change. It was established in 1988 by the World Meteorological Organization and the United Nations Environment Programme, and later endorsed by United Nations General Assembly. uses the reference period 1850 to 1900 to represent pre-industrial temperature to measure the degree of global warming that has occurred. They say about this reference period in their 2018 report:-
In principle, ‘pre-industrial levels’ could refer to any period of time before the start of the industrial revolution. But the number of direct temperature measurements decreases as we go back in time. Defining a ‘pre-industrial’ reference period is, therefore, a compromise between the reliability of the temperature information and how representative it is of truly pre-industrial conditions. Some pre-industrial periods are cooler than others for purely natural reasons. This could be because of spontaneous climate variability or the response of the climate to natural perturbations, such as volcanic eruptions and variations in the sun’s activity. This IPCC Special Report on Global Warming of 1.5°C uses the reference period 1850–1900 to represent pre-industrial temperature. This is the earliest period with near-global observations and is the reference period used as an approximation of pre-industrial temperatures in the IPCC Fifth Assessment Report.
Global Warming of 1.5°C – IPCC Report
I thought I would look and see how the CETCET Central England Temperature series was doing and see if it was getting close to the magic +1.5°C. The daily mean maximum and minimum only began in 1878 so it’s not possible to calculate mean values using this data, but daily mean temperatures are available back to 1772, and so it’s possible to calculate a mean for 1850-1900. It’s also possible to go back further and calculate a mean from 1772-1900, or better still calculate a mean for the period 1772-1850, which in my opinion is a better start for the dawn of the industrial era or the industrial revolution.
The anomalies in the bar chart are larger than you would normally see because I’ve based them on a long-term average for the period 1851-2000. Annual mean anomalies nearly exceeded 1.5°C back n 1949, and in recent years the 1.5°C barrier has been breached at least six times including this year (2022) which looks likely to become the warmest year on record. So we’ve not quite reached the +1.5°C mark globally but we are not far off in central England. I wonder what Gordon Manley would make of it all?
What caused the cooling between 1950 and 1980 in global as well as temperatures in central England? Maybe it was the airborne testing of thermonuclear weapons that followed the second world war and which continued till around 1976 according to Wikipedia. Natural variability or man made? My money’s on the latter in this case.
