Guest ridicule by David Middleton
Anthony covered this story a couple of days ago: MIT: Climate tipping point busted – globe needs to reach 152°F before runaway greenhouse effect kicks in.
When I saw this headline on Real Clear Science, I assumed it had to be about some other study…
But… No… It was an article about the same MIT study…
NEWS CLIMATE 26 SEPTEMBER 2018
A warming Earth might eventually copy the greenhouse effect of Venus
Modelling finds the precious equilibrium between temperature and radiation breaks down beyond a certain point, spelling big trouble. Alan Duffy reports.
Climate models show a warming Earth radiates more heat into space, but when pushed too far, and this release valve shuts down, temperatures skyrocket to potentially Venusian levels.
Now, climate models published in the journal Proceedings of the National Academy of Science, calculated by researchers at the Massachusetts Institute of Technology’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), have revealed why this linear relation holds – and when it may break down to the detriment of all life.
Confident in their model, the EAPS team then cranked up the surface to ever hotter temperatures, finding that the simple linear relation broke down at 300 °K (27 °C). Above this threshold, the increasing temperature of the surface didn’t lead to a similar increase in the amount of heat escaping, thus trapping more heat.
The rising surface temperature led to more water in the atmosphere, which in turn trapped the heat, causing ever higher temperatures, resulting in a runaway greenhouse effect. This process is believed to have occurred on Earth’s twin, the planet Venus.
Koll calculated that for Earth the runaway temperature threshold was at 340 °K (67 °C) – thankfully far beyond the current average surface temperature of about 285 °K (12 °C).
Such dramatic temperature rises could only be possible through cataclysmic events, such as increasing solar outputs over billions of years of the sun’s evolution. The EAPS work suggests that the more modest, yet still dangerous, climate change-inducing temperature rises the existing model predicts for Earth will see the linear relation hold true.
So, while Earth won’t go the way of Venus any time soon, a warming planet still means a hotter world despite the increasing heat escaping into space.
ALAN DUFFY is an astrophysicist at Swinburne University of Technology, Melbourne. Twitter | @astroduff
67 °C = 153 °F
27 °C = 81 °F
When was Earth’s average surface temperature 67 °C (153 °F) or above?
During the time known as the Hadean (yes, because it was like Hades), Earth’s collisions with other large planetesimals in our young solar system—including a Mars-sized one whose impact with Earth is thought to have created the Moon—would have melted and vaporized most rock at the surface. Because no rocks on Earth have survived from so long ago, scientists have estimated early Earth conditions based on observations of the Moon and on astronomical models. Following the collision that spawned the Moon, the planet was estimated to have been around 2,300 Kelvin (3,680°F).
Even after collisions stopped, and the planet had tens of millions of years to cool, surface temperatures were likely more than 400° Fahrenheit. Zircon crystals from Australia, only about 150 million years younger than the Earth itself, hint that our planet may have cooled faster than scientists previously thought. Still, in its infancy, Earth would have experienced temperatures far higher than we humans could possibly survive.
But suppose we exclude the violent and scorching years when Earth first formed. When else has Earth’s surface sweltered?
The Hadean Eon was from 4.6 to about 4.0 billion years ago and “our planet may have cooled faster than scientists previously thought”.
When was Earth’s average surface temperature 27 °C (81 °F) or above?
Not during the Cenozoic Era…
During the PETM, the global mean temperature appears to have risen by as much as 5-8°C (9-14°F) to an average temperature as high as 73°F. (Again, today’s global average is shy of 60°F.)
Even if CO2 played a role in the warmth of the Paleocene-Eocene, it has no relevance to the notion that a “warming Earth might eventually copy the greenhouse effect of Venus.”
Even with CO2 levels far higher than the Paleocene-Eocene, a “warming Earth” has never indicated that it “might eventually copy the greenhouse effect of Venus.”
The Phanerozoic Eon appears to have a equilibrium climate sensitivity of about 1.28 °C per doubling of atmospheric CO2. It would require over nine doublings of atmospheric CO2 just to raise the Earth’s average surface temperature from 15 to 27 °C. You can’t even get there with RCP8.5.
A “warming Earth” can’t “eventually copy the greenhouse effect of Venus.” Only a warming Sun or some other astrophysical/geophysical catastrophe could accomplish this task. Dr. Duffy alludes to this near the end of the article. However the headline and intimation that a “warming Earth might eventually copy the greenhouse effect of Venus” are grossly irresponsible. Allan Duffy is supposedly an astrophysicist/astronomer, who has won awards for science communication.
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