From
Nature volume 571,
pages550–
554
(
2019):
No evidence for globally coherent warm and cold periods over the preindustrial Common Era
Earth’s climate history is often understood by breaking it down into constituent climatic epochs
1. Over the Common Era (the past 2,000 years) these epochs, such as the Little Ice Age
2,3,4, have been characterized as having occurred at the same time across extensive spatial scales
5. Although the rapid global warming seen in observations over the past 150 years does show nearly global coherence
6,
the spatiotemporal coherence of climate epochs earlier in the Common
Era has yet to be robustly tested. Here we use global palaeoclimate
reconstructions for the past 2,000 years, and find no evidence for
preindustrial globally coherent cold and warm epochs. In particular, we
find that the coldest epoch of the last millennium—the putative Little
Ice Age—is most likely to have experienced the coldest temperatures
during the fifteenth century in the central and eastern Pacific Ocean,
during the seventeenth century in northwestern Europe and southeastern
North America, and during the mid-nineteenth century over most of the
remaining regions. Furthermore, the spatial coherence that does exist
over the preindustrial Common Era is consistent with the spatial
coherence of stochastic climatic variability. This lack of
spatiotemporal coherence indicates that preindustrial forcing was not
sufficient to produce globally synchronous extreme temperatures at
multidecadal and centennial timescales. By contrast, we find that the
warmest period of the past two millennia occurred during the twentieth
century for more than 98 per cent of the globe. This provides strong
evidence that anthropogenic global warming is not only unparalleled in
terms of absolute temperatures
5, but also unprecedented in spatial consistency within the context of the past 2,000 years.
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