Buried deep in the pages of the report are several graphs claiming to show that the average temperature of the Earth has been warming since the beginning of the industrial revolution. One of the more infamous graphs is the Northern Hemisphere Temperature Reconstruction Graph (below). This graph leaves off the Antarctic continent where routinely temperatures are recorded at well below -40o Celsius. The coldest temperature on Earth ever recorded was -89o C was at Vostok Station on the Antarctic plateau in 1983. This Northern Hemisphere only temperature graph, was plotted with an accuracy of one tenth of a degree Celsius, and is touted as strong "evidence" for what has been termed Anthropogenic Global Warming (AGW). The devil is in the details, as they say.
So just what are details concerning the accuracy of these temperature graphs? The data that went into compiling the graph above were of two types. The earliest plots are derived from proxy data and the more recent plots are from instrument derived data. Proxy data is indirect data taken from tree rings, coral or sediments. Instrument data is theoretically the most accurate because it is actually recorded off a thermometer or other calibrated sensors. Reconciling the different sets of data is supremely difficult. The techniques used to reconcile the data create known values of error termed margins of error. Yet there are no error bars plotted on this Northern Hemisphere only graph. Is this just an oversight?
Looking closely at the graph reveals a significant problem. None of the proxy data derived temperature traces agree with each other. Specifically just after A. D. 1600 the temperature trace in lavender shows temperatures cooling while the blue line shows that temperatures are warming. In each case the trends are less than two tenths of a degree Celsius in variance. Read more.
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