From NoTricksZone

By Kenneth Richard 

Atmospheric pressure may have been over 2.0 bar during the Jurassic, which may explain why Antarctica was a densely vegetated rainforest during that time.

It has long been understood that atmospheric pressure is one of the primary determinants of a planet’s temperature, with higher pressure (for example, Venus at 92 bar) yielding warmer climates due the increase in heat capacity with mass (Chemke et al., 2016, Chemke et al., 2017), and lower pressures (Mars at 0.006 bar, Earth at 1.0 bar) yielding cooler climates (Goldblatt et al., 2009, Sorokhtin et al., 2007).

What we know about the requisite physics for the aerodynamics of flight (e.g., how heavy is too heavy for lift-off) serves as a robust proxy for atmospheric pressure variations of the ancient past.

For instance, the “giant birds of the Miocene,” with wingspans of “6.5 m or more,” could not take flight with today’s air densities (Cannell, 2020). Knowing what we know about flight physics, a minimum air pressure of 1.3 bar “would have been necessary for these birds to fly.”

Using known size and flight physics for large-winged predators, scientists have concluded the Late Permian and Middle to Late Jurrassic may have had atmospheric pressures of over 2 bar (Cannell and Nel, 2023). This could explain the polar warmth allowing for an Antarctic rainforest near the South Pole ~90 million years ago (Klages et al., 2020).

A new study provides a visual for just how much pressure may have varied in the past, ranging from 0.5 bar ~350 Ma to ~2.5 bar 300 Ma, and then almost 2.0 bar ~100 Ma, or during the time of the dinosaurs. (See the chart provided.)

As mentioned, one salient effect of atmospheric pressure variations is the size of animal and plant species, with higher pressures and greater warmth yielding 60-70 m tall trees, giant wing-extended (volant) insects and birds, alligators and magnolias thriving at the North Pole during the Eocene (~50 Ma), etc.

An interesting section of the paper suggests that not only does a planet’s atmospheric pressure determine the global temperature and the size of its creatures, it also may determine atmospheric CO2 levels and how alkaline or acidic the oceans get.

As noted in another recent paper, global temperatures and atmospheric CO2 are significantly negatively correlated (r = -0.76) over the last 210 million years (Davis, 2023). Likewise, high CO2 levels are associated with cooling periods like the End Permian extinction event, but not with ocean acidification periods. This strongly suggests atmospheric CO2 levels are not the determinant of the oceans’ pH balance nor global temperature – as we are led to believe.

“Periods of high atmospheric CO2, such as the Devonian, but with non-acidic oceans…are of particular interest. Oceans absorb a large amount of CO2 (currently ~50 times that of the atmosphere) due to the relatively high solubility of this gas in seawater, as expressed by Henry’s constant. A reduction in atmospheric mass therefore leads to massive outgassing of fractionated CO2 into the air and relatively alkaline seas. This is seen in the Devonian, at the end Permian and the Triassic-Jurassic transition, as well as in many major cooling events that take place together with an increase in CO2. Conversely, an increase in atmospheric pressure increases absorption and leads to lower levels of atmospheric CO2, but more acidic seas.”