Much of the media discussion about last week’s Fifth Assessment Report of the Intergovernmental Panel on Climate Change centred on the ‘slowdown’ in the rate of rise of Global Mean Temperature. This was held up by sceptics as evidence that climate models were unreliable.
While preparing for a forthcoming conference, I re-plotted the data for the temperature rise above the land surfaces of the Earth and took a close look at the graph. I was shocked at just how insignificant this ‘temperature hiatus’ appeared to be. You can judge its significance for yourself. The ‘details’ section below has … wait for it… ‘detailed information’ about the data.
The black dots represent the best estimate of the ‘anomaly’ for each year. i.e. the difference from the average value between 1961 and 1990. The red lines join the dots to give an unbiased impression of ‘trend’. The grey bars above and below each point show the range of values within which the team at the Climate Research Unit are confident that the true value lies.
After recovering from my surprise I had three thoughts:
- My first thought was to reflect that when we discuss this issue in Protons for Breakfast we pay almost no attention to this data. Although the graph is iconic it really is not part of the main discussion. In fact it is really a triumph of scientific endeavour that we have managed to reconstruct it all!
- My second thought was how interesting it was that sceptics have moved on from saying this graph is unbelievable because it is based on unreliable data and analyses. Now they say they believe it and find significance in essentially random details that support their view that climate science is somehow ‘wrong’.
- My third thought was to wonder what will happen next: And of course the answer is “we don’t know” – its the future, and climate is complicated.
But whether you can see a ‘hiatus’ in this data or not, it is clear that rate of temperature change is much slower than the rate at which governments change, but still fast enough to be significant within a single lifetime. Even for a 53 year-old like me.
The data plotted is from the so-called CRUTEM3 analysis of land surface temperatures. The ‘CRU’ refers to the Climatic Research Unit of East Anglia University. The ‘TEM’ refers to temperature and the ‘3’ is the version number.
CRUTEM3 is an analysis of historical meteorological data of the air temperature approximately one metre above the land surfaces of the Earth. The input to the analysis are thousands of data series from individual meterological stations. The analysis searches for errors in these series (and there are lots!) and attempts to find trends in the data.
You can download the data from this page of the Met Office Web SIte. This page also has an analysis of the sea surface temperatures, and the combined sea and land surfaces of the Earth.
Downloading and plotting graphs can be tricky because the data is in a very basic format (described here) but it is interesting. The data are archived in this primitive form in order to keep them universally accessible. However if you prefer to look at the data using a commercial spreadsheet, you can download the spreadsheet (.xslx) into which I put the data here: CRUTEM 3 Anomaly.