Global climate change Data

How have we come to be told that global temperatures have suddenly taken a great leap upwards to their highest level in 1, 000 years? In fact, it has been no greater than their upward leaps between 1860 and 1880, and 1910 and 1940, as part of that gradual natural warming since the world emerged from its centuries-long “Little Ice Age” around 200 years ago.

This belief has rested entirely on five official data records. Three of these are based on measurements taken on the Earth’s surface, versions of which are then compiled by Giss, by the US National Oceanic and Atmospheric Administration (NOAA) and by the University of East Anglia’s Climatic Research Unit working with the Hadley Centre for Climate Prediction, part of the UK Met Office. The other two records are derived from measurements made by satellites, and then compiled by Remote Sensing Systems (RSS) in California and the University of Alabama, Huntsville (UAH).

The adjusted graph from the Goddard Institute for Space Studies

In recent years, these two very different ways of measuring global temperature have increasingly been showing quite different results. The surface-based record has shown a temperature trend rising up to 2014 as “the hottest years since records began”. RSS and UAH have, meanwhile, for 18 years been recording no rise in the trend, with 2014 ranking as low as only the sixth warmest since 1997.

One surprise is that the three surface records, all run by passionate believers in man-made warming, in fact derive most of their land surface data from a single source. This is the Global Historical Climate Network (GHCN), managed by the US National Climate Data Center under NOAA, which in turn comes under the US Department of Commerce.

But two aspects of this system for measuring surface temperatures have long been worrying a growing array of statisticians, meteorologists and expert science bloggers. One is that the supposedly worldwide network of stations from which GHCN draws its data is flawed. Up to 80 per cent or more of the Earth’s surface is not reliably covered at all. Furthermore, around 1990, the number of stations more than halved, from 12, 000 to less than 6, 000 – and most of those remaining are concentrated in urban areas or places where studies have shown that, thanks to the “urban heat island effect”, readings can be up to 2 degrees higher than in those rural areas where thousands of stations were lost.

Below, the raw data in graph form

To fill in the huge gaps, those compiling the records have resorted to computerised “infilling”, whereby the higher temperatures recorded by the remaining stations are projected out to vast surrounding areas (Giss allows single stations to give a reading covering 1.6 million square miles). This alone contributed to the sharp temperature rise shown in the years after 1990.

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