Dozens of rapid warming and cooling periods episodically occurred throughout the last glacial. However, they have often been dismissed as local-only events. A 2020 study published in Science robustly affirms steeper-than-today warming periods spanned both hemispheres and 23 of 25 were “globally synchronous.” 

Geologists have long recognized that Greenland abruptly warmed up by 5 to 16°C “within a few decades to centuries” about 25 times in the last ~100,000 years (Capron et al., 2021).

These past abrupt climate changes do not even require a clear external trigger to explain their provenance. They can simply be “unforced or noise-induced oscillations” internal to the climate system (Capron et al., 2021Li and Born, 2019).

Image Source: Capron et al., 2021

The magnitude and rapidity of the temperature changes occurring during the last glacial were many times greater than what has been observed in the modern era.

In the last 100 years , for example, Greenland has not experienced any obvious net warming. In fact, not only was the “1919–32 warming trend […] 33% greater in magnitude than the 1994–2007 warming” (Box et al., 2009), but the Greenland ice sheet has not warmed (net) since the early 2000s.

Globally, the  average warming rate is just 0.05°C per decade since 1860 (Zhu et al., 2018).

Image Source: Zhu et al., 2018

When it’s pointed out that there were about 25 unforced, naturally-occurring abrupt climate changes (called interstadials) much faster and of much greater magnitude than the last few centuries, those wishing to advance the claim that modern warming is human-induced and unprecedented typically suggest these past warming episodes were just local changes specific to Greenland.

But a growing body of evidence from 63 independently published records has led scientists to conclude there was “synchronous timing” (within a few decades) spanning the entire globe – from Greenland to Antarctica to the tropics and mid-latitudes – for 23 of these 25 warming episodes (Corrick et al., 2020).

In other words, modern global warming is no more “special” in its magnitude or speed than the much larger unforced global climate changes internal to the climate system pervading the last glacial period.

Image Source: Corrick et al., 2020

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July 29, 2021