Earth’s average annual temperature fluctuated by as much as 35°C (at high latitudes) from one millennial-scale period to the next during the last glacial period.
A recently-published 2-part study (Smul′skii, 2022a and 2022b) utilizes established orbital and insolation data to calculate Earth’s average temperature today (0 k years ago), 14.4°C, and at 25°N, 45°N, 65°N, 80°N, 0°, -25°S, -45°S, -65°S, and -80°S during 3 paleo epochs: 15.9 k years ago, 31.3 k years ago, and 46.4 k years ago.
Global annual temperature of Earth: 14.4°C – the same as a century ago
Consistent with dozens of other calculations, Smul′skii (2022a) determined the mean annual temperature of the modern period, which includes 1991-2018, ranges between 14.07 and 14.41°C.
This calculation is similar to what Jones et al. determined as Earth’s temperature in a 1999 study: 14.0°C.
Image Source: Jones et al., 1999
Kramm et al., (2020) reported the generally agreed-upon global temperature from 1877 to 1913 from dozens of calculated results was also about 14.4°C.
HadCRUT, Berkley, and NASA GISS indicate the 1991-2018 period’s global annual surface temperature has also been 14.5°C. Thus, as these geoscientists conclude, there has been “no change in the globally averaged near-surface temperature over the past 100 years”.
Image Source: Kramm et al., 2020
The global annual temperature was warmer than today during the last glacial period
Even though atmospheric CO2 concentrations were said to be about 200 ppm 31.3 k years ago, or during the last glacial, Earth was significantly warmer than it is today – especially at the higher latitudes.
At 65°N, for example, the mean annual temperatures were 0.66°C 31.3 k years ago, but -5.6°C today. In other words, it was 6.3°C warmer during the last glacial at this latitude.
At 90°N, mean annual temperatures were -2.65°C 31.3 k years ago, but -25.3°C today. The modern North Pole is thus ~22°C colder than it was during the “Karginsky Interglacial” (31.3 k years ago). At 90°S, mean annual temperatures were ~27°C warmer than today (-31.1°C vs. -4.1°C) 31.3 k years ago.
Image Source: Smul’skii, 2022b
Averaged over the entire Earth, the mean annual temperature was 0.4°C warmer than modern (14.8°C) 31.3 k years ago, and -0.4°C colder than modern (14.0°C) 46.4 k years ago, or during the coldest period in the last 200,000 years.
Mean annual temperature swings ranging from -3.4°C at 80°N 111.8 k years ago to -40.9°C at 80°N 46.4 k years ago suggest millennial-scale climate variations as high as 35°C occur naturally in the Earth’s climate system.
Other paleoclimate studies also document a warm period 31.3 k years ago
These global to regional temperature variations are consistent with independent paleoclimate research. For example, about 31.3 k years ago (“31,436 – 31,178 cal BP”) temperatures in the Russian Altai mountains (49°N) were thought to be 5.9°C warmer than today (Ganyushkin et al., 2018) given the presence of tree remains at much higher altitudes (500 m) than the modern tree line dating to that period.
Image Source: Ganyushkin et al., 2018
Scientists document a Siberian Arctic with “warmer-than-today temperatures (by up to 4 – 4.5°C)…between about 39 and 31 cal kyr BP” (Wetterich et al., 2021).
Image Source: Wetterich et al., 2021
There were ~5°C warmer glacial climates (July) than today throughout Northern Asia during the millennia between 50 k and 20 k years ago (Tarasov et al., 2021).
“…reconstructed mean July temperatures above 12°C for most of the last cold stage [glacial] in the study area [throughout Northern Asia], where modern mean July temperatures are about 7°C”.
The widespread presence of grazing mammoths, horses, bison, deer, antelope, gazelle…in Siberia and Alaska and well north of the Arctic circle imply “year-round grazing grounds.” This requires warmer temperatures and more pervasive ice-free grass-grazing ranges than exist today.
Image Source: Tarasov et al., 2021
In the North Pacific ~35 k to 18 k years ago temperatures ranged between 10 and 16°C versus 9.1°C today (Max et al., 2020).
Image Source: Max et al., 2020
In southern California temperatures reached 22-23°C 31 k to 24 k years ago, whereas they are only 18°C today (Feakins et al., 2019).
Image Source: Feakins et al., 2019
In the Southern Hemisphere, the Southern Ocean’s surface temperatures peaked at 13.6°C about 22 k years ago. From 35 to 30 k years ago temperatures ranged from 12-13°C versus 8.5°C today (3.5 to 4.5°C warmer). There were “higher SST during the 40-24 kyrs period than during the Holocene” (Civel-Mazens et al., 2021).
Image Source: Civel-Mazens et al., 2021
It was 2-5°C warmer than today in the South Atlantic from about 65 k to 30 k years ago, “prompting us to exclude atmospheric pCO2 as a direct driver of SST variations in the southern WTA [Western Tropical Atlantic]” (Hou et al., 2020).
Image Source: Hou et al., 2020
In sum, none of these studies support the conclusion that CO2 concentrations are a driver of surface temperatures. Earth’s mean annual temperatures have been much warmer (or colder) than today, regardless of the CO2 concentration.