We quote the last part of this Phys.org article, headed: ‘A planet Earth in a fragile equilibrium.’ Somehow the model finds that once the oceans have eventually evaporated ‘we would even reach 273 bars of surface pressure and over 1,500°C’. This seems a bit unlikely on the face of it as it’s three times the surface pressure, and temperature [note the link between those two] of Venus despite being nearly 40% further away from the Sun. We note that it’s not unheard of for climate models to over-predict temperature effects.
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Talkshop note – the article earlier states:
One of the key points of the study describes the appearance of a very peculiar cloud pattern, increasing the runaway effect, and making the process irreversible. “From the start of the transition, we can observe some very dense clouds developing in the high atmosphere. Actually, the latter does not display anymore the temperature inversion characteristic of the Earth atmosphere and separating its two main layers: the troposphere and the stratosphere. The structure of the atmosphere is deeply altered,” says Chaverot.
. . .
A planet Earth in a fragile equilibrium.
With their new climate models, the scientists have calculated that a very small increase of the solar irradiation—leading to an increase of the global Earth temperature, of only a few tens of degrees—would be enough to trigger this irreversible runaway process on Earth and make our planet as inhospitable as Venus.
One of the current climate goals is to limit global warming on Earth, induced by greenhouse gases, to only 1.5° by 2050.
One of the questions of Chaverot’s research grant is to determine if greenhouse gases can trigger the runaway process as a slight increase of the sun luminosity might do.
If so, the next question will be to determine if the threshold temperatures are the same for both processes.
The Earth is thus not so far from this apocalyptical scenario.
“Assuming this runaway process would be started on Earth, an evaporation of only 10 meters of the oceans’ surface would lead to a 1 bar increase of the atmospheric pressure at ground level. In just a few hundred years, we would reach a ground temperature of over 500°C. Later, we would even reach 273 bars of surface pressure and over 1,500°C, when all of the oceans would end up totally evaporated,” concludes Chaverot.
Full article here.
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From the research article:
The key process allowing a runaway greenhouse is the evaporation of the surface ocean. To model the ocean, we used a two-layer slab ocean without heat transport, coupled to the atmosphere (see Sect. 2.2). Evaporating the totality of the Earth’s oceans will induce a vapor surface pressure of 273 bar. Regarding the large heat capacity of the water vapor, any temperature modification will be extremely slow in this situation, making such a simulation unachievable from a numerical point of view. Moreover, the timescale required to evaporate enough water to reach this pressure are also hugely long. [bold added]
First exploration of the runaway greenhouse transition with a 3D General Circulation Model (2023)
via Tallbloke’s Talkshop
December 28, 2023 at 11:09AM
Iowa Climate Science Education 