Recent global temperature “plateau” in the context of a new proxy reconstruction

Abstract:

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, when carbon dioxide concentration was at preanthropogenic 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°C ± 0.2°C warmer than the nonvolcanic 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.