Wiley Open Access, Earth's Future, 5(2), p. 281-294, 2014
DOI: 10.1002/2013ef000216
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Stable global temperatures of the last 10-15 years have been a topic of considerable discussion. A new proxy extension of the global temperature record enables better placement of this feature in a longer historical perspective. The fixed-grid composite covers the interval 1801-1984, with an extension to 1782 and anchors the global temperature record in the last major cold interval of the Little Ice Age (LIA), when carbon dioxide concentration was at pre-anthropogenic levels. Except for greater and longer cooling (approximately twice the length of Pinatubo) associated with the Tambora eruption, the proxy agrees with the most widely-cited previous assessment of global temperature over this interval, lending more confidence to a centennial extension of the global temperature record. The proxy correlation is as high as 0.83 for the interval 1907-1984 (df = 8, p = 0.001), with the 21st century 1.0 ± 0.2˚C warmer than the non-volcanic base state. This remarkable linearity requires a clear theoretical understanding as to how an exceedingly complex system can, on the global average, behave in such a simple way. Removal of the linear radiatively-forced component from the global temperature record yields an estimate of natural variability for the last 230 years and indicates no unusual natural variability during the recent 10-15 years. Based on the estimate of unforced variability over the last 170 years, there is about a 40% chance of continued ‘natural cooling’ over the next few years, with about a 10% chance of cooling persisting into the next decade.