Was the Warming of the Late 20th Century Unprecedented?

Those who claim that the effects of man's emissions of carbon dioxide on climate are catastrophic, have commonly said the high temperatures of the late 20th Century and the rate of their rise was unprecedented.  All of the extensive evidence of warm periods in Europe and around its periphery is often said to be only due to local effects, without a worldwide analog.  Over the last 10 years more evidence that these warm events existed in places such as China and South America has been found, but the non-European evidence is not so voluminous that those who make the claim of unprecedented warming recently have been quieted.  A new study of sea surface temperatures in the East China Sea over the last 2700 years adds to that evidence that the recent history has precedents.


Weichao Wu of Peking University and 4 other colleagues of various universities in China collected a sediment core from the sea floor in the Southern Okinawa Trough over which the warm Kuroshio current flows.  "The researchers analyzed the top 10 meters of the sediment core, corresponding to 2,700 years of sedimentation and from it were able to resolve 25-yr averages. To determine the SST, they used the “relative number of cyclopentane isoprenoid GDGTs in marine crenarchaeota (Thaumarchaeota)” which “increases with increasing growth temperature.”""  "...they identified a tracer in the sediment layers that is a measure of the relative abundance of a tiny marine organism whose number is sensitive to the sea surface temperature. The more crenarchaeota that are evident in the sediment layer, the higher the ocean temperature."

The temperature history from this proxy reconstruction is shown in the graph below with data points for each 25-year average and a running three-point mean line. 



Their sea surface temperature reconstruction clearly shows the Roman Warm period (RWP), the Dark Age Cool Period (DACP),  the Sui-Tang dynasty Warm Period (STWP),  the Medieval Warm Period (MWP), the Little Ice Age (LIA), and the Current Warm Period (CWP). The warm period from 500 to 350 BC was when Persian and Greek civilizations arose.  The highest temperature data point for this period is higher than any for the recent CWP.  The rate of rise at its start is also faster.  The highest temperature in the RWP is also higher, as is the rate of initial rise in temperature for the RWP, compared to the CWP.  The STWP seems to have displaced a longer Dark Ages Cool Period in Europe.  The highest temperature in the MWP in the East China Sea is higher than the recent warming also, though the MWP in Europe was more substantial than that in the East China Sea.

The important thing is that higher temperatures and higher rates of temperature increase, as well as higher rates of temperature decrease, have occurred in the past in other areas of the world with a significant correlation to the events of Europe and its surroundings.  The temperature proxy data used to construct the hockey stick temperature record of the last IPCC assessment report was very limited.  As pointed out by Ian Plimer in Heaven and Earth global warming the missing science, there actually is much information from around the world that indicates how misleading that hockey stick temperature plot really was.