“Venus was Earth-like once more, however local weather change made it uninhabitable” – Watts Up With That?
Guest essay by Eric Worrall
Despite the disturbing title, the authors are not trying to say that if we don’t improve our wicked ways, the earth will end up like Venus. But the Forbes article and study models postulating an early ocean-covered Venus seem to make many assumptions, with very little evidence to guide those assumptions.
Venus was Earth-like again, but climate change made it uninhabitable
December 14, 2020 12:04 p.m. AEDT
Richard Ernst
Scientist-in-Residence, Geosciences, Carleton University (also Professor at Tomsk State University, Russia), Carleton University
We can learn a lot about climate change from Venus, our sister planet. Venus currently has a surface temperature of 450 ° C (the temperature of a furnace’s self-cleaning cycle) and a carbon dioxide (96 percent) dominated atmosphere with a density 90 times the density of Earth.
Venus is a very strange place, completely uninhabitable except maybe in the clouds about 60 kilometers high, where the recent discovery of phosphine could point to floating microbial life. But the surface is completely inhospitable.
However, Venus probably once had an Earth-like climate. According to recent climate models, Venus had surface temperatures similar to today’s Earth for much of its history. It probably also had oceans, rain, maybe snow, maybe continents and plate tectonics, and even more speculative, maybe even surface life.
Less than a billion years ago, the climate changed dramatically due to a runaway greenhouse effect. It can be speculated that an intense period of volcanism pumped enough carbon dioxide into the atmosphere to cause this major climate change event that evaporated the oceans and caused the end of the water cycle.
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Read more: https://theconversation.com/venus-was-once-more-earth-like-but-climate-change-made-it-uninhabitable-150445
The abstract of the study;
Was Venus the first habitable world in our solar system?
MJ Way, Anthony D. Del Genio, Nancy Y. Kiang, Linda E. Sohl, David H. Grinspoon, Igor Aleinov, Maxwell Kelley, Thomas Clune
Today’s Venus is an inhospitable place with surface temperatures close to 750 K and an atmosphere 90 times thicker than that of Earth. Billions of years ago the picture may have been very different. We created a series of 3-D climate simulations that included topographical data from the Magellan’s mission, spectral solar radiation estimates for 2.9 and 0.715 Gya, current Venus orbital parameters, ocean volume consistent with current theory, and estimated atmospheric composition use early Venus. Using these parameters, we find that such a world could have had moderate temperatures if Venus had had a progressive period of rotation slower than ~ 16 Earth days, despite an incoming solar flux that is 46-70% higher than that Earth. In the current rotation period, the climate of Venus could have remained habitable up to at least 0.715 Gya. These results show the role rotation and topography play in understanding the climatic history of Venus-like exoplanets discovered in the current epoch.
Read more: https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2016GL069790
The assumptions behind this modeling exercise appear to be a significant stretch. For example;
Venus was resurfaced hundreds of millions of years ago through volcanic activity [e.g., McKinnon et al., 1997; Kreslavsky et al., 2015]Hence, its topography is unknown before that time. We use modern topographical data from the Venus Magellan mission via the PDS archive (Planetary Data System) (http://pds‐geosciences.wustl.edu/mgn/mgn‐v‐rss‐5‐) as an estimate on an observation basis – l2 – v1 / mg_5201) and fill the re-emerged lowland with water.
Read more: Same link as above
The postulated periodic “emergence” of Venus is far more violent than any volcanic event that was ever known to have occurred on Earth. The basis of the resurfacing theory is the absence of impact craters on Venus. The estimated age of the observed impact craters suggests that the entire surface of Venus was covered with lava or otherwise destroyed in a violent volcanic eruption about 300 million years ago. It seems like a big assumption that the previous surface topography of Venus roughly matched the current topography.
What about the initial atmospheric conditions? Here the models again assume that the initial atmospheric conditions of Venus were similar to Earth.
… In view of the fact that Venus has a significant N2 in its atmosphere today and has few modern sources or sinks (unlike Earth), we assume that an ancient Venus had an N2 atmosphere of ~ in its early history 1 bar (1012.6 mb) could have had. A modern amount of CO2 and CH4 is also included (400 ppm, 1 ppm), since these gas concentrations are otherwise only insufficiently restricted. …
Read more: https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2016GL069790
Don’t get me wrong, speculative modeling is obviously an interesting intellectual exercise and can be useful for exploring model boundaries or boundaries. But I think it would be a big leap to believe that models struggling to explain Earth’s current climate can tell us something meaningful about events that happened on another planet hundreds of millions of years ago.
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