Guest post by Dr. Don J. Easterbrook
Dept. of Geology, Western Washington University, Bellingham, WA
In a paper entitled “Current global warming appears anomalous in relation to the climate of the last 20 000 years,” Svante Björck claims that, over the past 20,000 years, there have been no world-wide, synchronous, climate changes until recently and that shows CO2 must be the cause of recent global warming. He claims that:
It is, however, virtually impossible to find evidence for globally synchronous climate events with the same climate signature, for example warmings or coolings.” “When the last ca. 20 000 yr of climate development is reviewed, including the climatically dramatic period when the Last Ice Age ended, the Last Termination, it appears that the last centuries of globally rising temperatures should be regarded as an anomaly.”
“…..no globally consistent climate event prior to today’s global warming has been clearly documented” so ….“we ought to regard the ongoing changes as anomalies, triggered by anthropogenically forced alterations of the carbon cycle.”
This apparent return to the ‘hockey stick’ argument includes denials of the global Roman warm period, the Dark ages cold period, the Medieval Warm Period, and the Little Ice Age.
“The often-cited climate pattern of the last 2000 to 3000 yr with the Roman Warm Period, the Dark Cold ages, the Medieval Warm Period and the Little Ice Age (LIA) seems to be restricted to the NH or parts of it, and does not show up as a global pattern of warmings and coolings. it is important to note that while the LIA was not a period of global cooling.”
Claims such as these can only be considered geofantasy, unsupported by scientific data and contrary to a vast amount of data to the contrary. For example, Björck claims that the large swings in temperature at the end of the last Ice Age, especially during the Younger Dryas (YD), were not global despite many peer-reviewed papers (when peer review meant something) documenting the global extent of the YD. The magnitude and intensity of late Pleistocene climate changes were much, much greater than recent warming and cooling (Fig.1).
Figure 1. Greenland ice core data showing abrupt warming and cooling events during the past 25,000 years. As shown by corresponding expansion and contraction of glaciers worldwide, these were globally synchronous events.
The Greenland isotope ice core data is well correlated with glacier advance and retreat in the European Alps, Scotland, Sweden, Norway, Finland, Russia, the Rocky Mts., the Cascade Mts., Sierra Nevada, Argentina, Chile, New Zealand, and various other places. The global record of non-glaciated areas is also clear in Asia, Australia, New Zealand,, North and South America, Europe, Russia, and elsewhere. There is a vast literature documenting all of these globally synchronous climate changes that Björck obviously needs to read.
The Younger Dryas abrupt and intense climate changes are not only globally synchronous, but are in fact practically simultaneous in both the Northern and Southern Hemisphere (see for example, Easterbrook 2011, Evidence for synchronous global climatic events: cosmogenic exposure ages of Pleistocene alpine glaciations, Elsevier). Figure 2, shows that not only is the Younger Dryas globally synchronous, but that advances within the YD can also be correlated globally, including examples from continental ice sheets in Scandinavia and North America, and alpine glaciers in the Cascade and Rocky Mts. of North America, the European Alps, and the New Zealand Alps, among many others.
Figure 2. Global correlation of phases within the Younger Dryas.
Globally synchronous Little Ice Age glacial advances and retreats are also well documented in the geologic literature, as well as the Medieval Warm Period. Well-defined glacial moraines lie downvalley from almost every glacier in the world!
How Björck can ignore this immense amount of data showing globally synchronous climate changes is very difficult to understand. His claim of no globally synchronous climate changes in 20,000 cannot be considered credible.