Reasons exist to have serious investigations of the whole of climate change (aka global warming) science.
Global warming inevitably rests on current temperatures setting records in geologic time, or at least since early human civilization. And this is where the 1998 Nature article by Michael Mann, Raymond Bradley, and Malcom Hughes depicting what has become known as the iconic “hockey stick” graph becomes critical. The “hockey stick” showed modern temperatures far hotter than in the year 1400.
The hockey stick graph was adopted into the third assessment report (2001) of the United Nations Intergovernmental Panel on Climate Change (IPCC) and contradicted a chart that had appeared only eleven years before in an earlier IPCC assessment report. The hockey stick eliminated what had traditionally been considered the hottest era, the Medieval Warm Period.
As reasonably accurate thermometers were not developed until well into the 19th century, one would wonder how earlier temperatures were measured. The answer is the use of proxy data – namely, ice cores, tree rings, bee pollen, ocean and lake sediment. But a reasonable person would have to wonder by what standards these items are interpreted.
This leaves only modern thermometer data sets, the primary one being that of the Goddard Institute for Space Studies Surface Temperature Analysis (GISTEMP), “an estimate of global surface temperature change … using current data files from NOAA [National Oceanic and Atmospheric Administration].” The entire 137-year monthly data set, from 1880 through June 2017, in degrees Celsius anomalies (deviations from the corresponding 1951-1980 means), updated monthly, is available in spreadsheet and text forms.
But the land and seas surface data from which the above is derived suffers serious flaws as far as indicating “global” warming. First of all, it is not, as implied, indicative of global surface temperatures. The NOAA website contains in the upper-left-hand corner a small and easily overlooked but important map denoting the location of land-based temperature measurement stations around the world and years of coverage, reproduced below. Not surprisingly, data for more than about 110 years exist only for the United States; Japan; southeastern Australia; and some areas in Europe, Asia, and India. Nearly all of Africa, South America, Antarctica, Alaska, northern Canada, Greenland, and Asia contain only a few decades of weather data, from widely dispersed stations.