CO2 concentrations have risen from 310 ppm to 410 ppm since the 1930s. However, there has been no net change in Arctic or Greenland temperatures during these last 90 years. During the Pliocene, CO2 also ranged between about 300-400 ppm, but the Arctic was 15-22°C warmer and sea levels 25 meters higher than today. Is CO2 really Earth’s “control knob”?
Nearly ten years ago, the imagery of a CO2 “control knob” for climate was canonized in the journal Science.
Image Source: Lacis et al., 2010
The CO2 concentration was said to determine – or control – Earth’s temperature.
However, the scientific literature’s paleoclimate record does not provide fundamental support for this paradigm of a CO2-controlled climate.
During the Ordovician, for example, CO2 concentrations reached 4,200 ppm – more than 10 times today’s levels. And yet the Earth returned to a glaciated “Snowball Earth” state during this period (Shuang et al., 2019).
Image Source: Shuang et al., 2019
The Arctic is a region where a significant percentage of the Earth’s recent warming has arisen, and consequently this warming has been linked to the rise in CO2 concentrations from about 310 ppm in the 1930s to 410 ppm today.
And yet scientists continue to publish papers indicating the 1930s warmth was similar to or greater than that of today (Araźny et al., 2019, Hanhijarvi et al., 2013) despite the sharp contrast in CO2 levels.
Image Source: Araźny et al., 2019
Image Source: Hanhijarvi et al., 2013
There has been no significant net warming in Greenland during the last 90 years according to newly published papers (Holme et al., 2019, Ruan et al., 2019, Vermassen et al., 2019, Khazendar et al., 2019) as well as other recent papers (Hanna et al., 2011, Kobashi et al., 2017, Mikkelsen et al., 2018).
Image Sources: Holme et al., 2019, Ruan et al., 2019, Vermassen et al., 2019, Khazendar et al., 2019
Image Source: Hanna et al., 2011
Image Source: Kobashi et al., 2017
Image Source: Mikkelsen et al., 2018
Is modern Greenland ice sheet melt significant?
During the Holocene Thermal Maximum (about ~9000 to ~7000 years ago), the Greenland ice sheet had about 500 meters less thickness than it has had in recent millennia, and its margins had retreated up to ~100 km behind their present-day position (Nielsen et al., 2018).
Image Source: Nielsen et al., 2018
The modern Greenland ice melt has amounted to an insignificant 15 mm since 1900 (Fettweis et al., 2017, Fettweis et al., 2008). That’s just 1.5 cm added to sea levels since the 20th century began – and no net contribution for the 60 years between the 1940s and 2000s.
Image Source: Fettweis et al., 2017
Image Source: Fettweis et al., 2008
The Pliocene Arctic was 15-22°C warmer than today despite similar CO2 levels
Cronin and Cronin ( 2015) reported that the Arctic Ocean was sea-ice-free and had temperatures reach a balmy 8-10°C three interglacials ago (MIS 11), when CO2 values peaked at 280 ppm. Polar bears somehow survived this much-warmer-than-today interval.
The same paper indicates the Arctic’s mean annual temperatures were 18.3°C warmer than today during the Pliocene, even though the Pliocene had CO2 concentrations similar to modern.
Image Source: Cronin and Cronin, 2015
A new paper indicates CO2 concentrations ranged between about 300 and 400 ppm during the Pliocene, but that Arctic mean annual temperatures were 15-22°C warmer than now (Fletcher et al., 2019) during this period.
Furthermore, all this polar warmth meant Earth’s sea levels were as much as 25 meters higher than present-day during the Pliocene.
Image Source: Fletcher et al., 2019
If CO2 was the Earth’s control knob, this is inconsistent with a “Snowball Earth” glaciation at 4,200 ppm, a sea-ice-free, 10°C to 22°C warmer Arctic at 280 ppm to 400 ppm, and no significant net change in Arctic/Greenland temperature as CO2 rose from 310 ppm to 410 ppm.