THAT A SELECTED CLIMATE EVENT IS UNPRECEDENTED DOES NOT PROVE THAT THE CURRENT WARM PERIOD MUST THEREFORE HAVE BEEN THE RESULT OF HUMAN CAUSE 

1. The climate science position that unprecedented climate events prove human cause of the current warming trend has no basis. That selected climate events can be found that are unprecedented proves only that they were unprecedented and not that therefore the current warm period must have a human cause.
2. For example, the PETM (Paleocene Eocene Thermal Maximum) ocean acidification event 55 million years ago is unprecedented in the paleo record but it was not human caused although it serves as the model for the ocean acidification fears in the current warm period.
3. The ETE (End Triassic Extinction) 200 million years ago is unprecedented in the paleo record but it was not human caused although it serves as a model for fears of a human caused mass extinction of the current warm period.
4. As for deglaciation transitions to interglacials, the extreme climate change events of the Eemian is unprecedented in the paleo record but it was not human caused although it serves as a model for a predicted catastrophic sea level rise event in the current warm period by way of a collapse of polar ice sheets.
5. Briefly, the lengths to which climate science has gone to prove human cause by arguing the case that various events in the current warm period are unprecedented is an oddity. That a climate event that is unprecedented is therefore human caused is not credible because it is illogical, unscientific, and without a rational basis.
6. The credibility of this argument is further weakened by the selection of arbitrary  reference time periods such as 1,000 years or 2,000 years for various claims to prove that the current warming is unprecedented.
7. CONCLUSION: Human cause must be proven in terms of the case against humans made in climate science u terms of the use of fossil fuels in the industrial economy, and not in terms of whether selected climate events in the current warm period is unprecedented. To do that it must first  be shown that being unprecedented requires a human cause.
8. The case against humans in climate science is that since the Industrial Revolution, humans have been releasing carbon dioxide into the atmosphere by burning fossil fuels and that this carbon dioxide is not in the current account of the carbon cycle but from carbon cycles millions of years ago.  It is thus argued that fossil fuel emissions of the industrial economy have caused atmospheric CO2 concentration to steadily increase and that steady increase has caused warming by way of the climate sensitivity of surface temperature to atmospheric CO2 concentration.
9. That climate science has now resorted to proving human cause by way of whether selected climate events in the current warm period are unprecedented may imply a weakness in the science.
10. Some sources of this weakness are explored in the related posts at these links
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