Responding to the CO2 Coalition's "Fact #14" on Glacial Cycles

CO2 Coalition's "Fact #14" appears to be pretty trivial, and as best I can tell, it exists here to scare people into being afraid of a coming ice age. Over the last million years (since the Mid-Pleistocene Transition), glacial cycles have been about 100K years long, synced with orbital cycles. For most of each glacial cycle, the Earth is in a glacial period, with continental ice sheets extending into mid-latitudes, but for about 10K-15K years, the Earth experiences an "interglacial" period, when global temperatures increase and continental ice sheets retreat. Our current interglacial, the Holocene, has lasted about 11,700 years, and the major ice sheets are restricted to Greenland and Antarctica. None of this is particularly controversial or relevant to whether AGW is causing harm to human civilization.

Now technically, the above graph shows the last 420K years of the current ice age. There are not multiple ice ages in the Quaternary. Even the interglacial periods are part of the Quaternary ice age. The graph should be labeled with glacial vs interglacial periods. But that's neither here nor there.

What is misleading is when they say that our current interglacial "may end within the next century or last another several thousand years." Then comes the scare tactic: "When the next ice age descends upon us, it will be a true climate apocalypse accompanied by crop failures, famine, mass emigration from colder to warmer regions and unprecedented population loss." This is a scare trick. Humans have increased CO2 levels to over 120 ppm higher than at any point during the Quaternary. At 420 ppm (and rising), we're pushing climate out of anything seen during the current ice age, and we're headed towards the type of global climate the Earth hasn't seen since the Mid-Pliocene 3 million years ago. And since CO2 stays in the atmosphere for thousands of years, we are not in danger of an ice age descending upon us "within the next century." We are actually more in danger of seeing the end of the Quaternary altogether.

A Geologic Perspective on CO2, from Rae et al 2021

In another post, I go into more detail about this possible future towards which we're heading, the best analog for which is the Mid-Pliocene. During that time, sea levels were 15-25m higher than today[3] and the Antarctic peninsula was below sea level.[1] Global temperatures were 2-4°C warmer than preindustrial temperatures[2][11], but due to polar amplification, the Arctic was much warmer. Latitudes farther north than 70°N were possibly 10°C warmer or more[1][2], and Greenland supported only an ephemeral ice sheet.[4] Instead, the Arctic supported boreal forests with at least 5 different kinds of pine trees.[5] One study of Lake El’gygytgyn in northeast Arctic Russia had summer temperatures ~8°C warmer than today between 3.6 and 3.4 million years ago and remained warmer than today until about 2.2 million years ago, when NH glaciation began.[4] Meanwhile, in Antarctica 5.3 to 2.6 million years ago, beech trees were growing at Oliver Bluffs, just 300 miles from the South Pole. Summer temperatures were perhaps +5°C, which is about 20°C to 25°C warmer than today. The West Antarctic ice sheet and some of the East Antarctic ice sheet would have been gone.[6][7].

Thankfully, with mitigation (and possibly carbon capture) this future is still avoidable. This is a possible future that is likely to occur if we fail to mitigate, but we can stabilize global temperatures to 2.0 to 2.5°C above preindustrial levels. The CO2 Coalition wants you to be terrified of climate stability and instead wants you to believe that the real threat is another ice age, and good things happen if the earth is warmer.

References:

[1] Alley RB, Clark PU, Huybrechts P, Joughin I. Ice-sheet and sea-level changes. Science. 2005 Oct 21;310(5747):456-60. doi: 10.1126/science.1114613. PMID: 16239468.
https://pubmed.ncbi.nlm.nih.gov/16239468/

[2] M. Robinson, “Pliocene Role in Assessing Future Climate Impacts” Eos 89, No. 49 (2008). https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2008EO490001

[3] IPCC AR4, 6.3.2 “What Does the Record of the Mid-Pliocene Show?” https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-chapter6-1.pdf

[4] Julie Brigham-Grette, “Pliocene Warmth, Polar Amplification, and Stepped Pleistocene Cooling Recorded in NE Arctic Russia” Science 340 (June 21, 2013).
http://science.sciencemag.org/content/340/6139/1421

[5] Stephanie Paige Ogburn etal. “Ice-Free Arctic in Pliocene, Last Time CO2 Levels above 400 PPM: Sediment cores from an undisturbed Siberian lake reveal a warmer, wetter Arctic.” SA
https://www.scientificamerican.com/article/ice-free-arctic-in-pliocene-last-time-co2-levels-above-400ppm/

[6] Rhian L.Rees-Owen. “The last forests on Antarctica: Reconstructing flora and temperature from the Neogene Sirius Group, Transantarctic Mountains” Organic Geochemistry Volume 118, April 2018, Pages 4-14
https://www.sciencedirect.com/science/article/pii/S014663801730219X

[7] Damian Carrington, “Last time CO2 levels were this high, there were trees at the South Pole.” The Guardian
https://www.theguardian.com/science/2019/apr/03/south-pole-tree-fossils-indicate-impact-of-climate-change