earth was once "venus like" before climate change
as is so often the case, the WEF has their story wrong way 'round
“before ‘climate change’ venus was once earth-like.” this claim has been making the rounds as some sort of cautionary tale for earth.
but like so much from the WEF, it sounds sensationalist but fails to stand up to scrutiny.
this analogy is inapt.
i know this is a bit of a frivolous analysis, but i just found it somehow fun to explore and this is such a wonderfully telling canard that i could not resist.
so let’s look:
foremost, venus is not really like current day earth. not today. not ever.
it’s much closer to the sun.
it has an atmosphere of astonishing mass, 93X that of earth resulting in 1,350 PSI of pressure at surface. this earth equivalent to being 3,000 feet under water.
the atmosphere is 96% CO2 (vs 0.04% on earth)
therefore, the mass of CO2 in venus’s atmosphere is ~223,000X that of earth.
humidity is >0.1%.
clouds are made of sulfuric acid and have massive albedo that reflect 75% of sunlight back into space. without this, venus would be MUCH hotter.
the top of earth’s atmosphere when pointed right at the sun gets 1,367 watts per square meter of solar energy. venus gets 2,636, roughly twice as much.
venusian surface light, despite much more energy at top of atmo, is 5-10k lux, equivalent to a partly cloudy day on earth.
despite this, surface temps are 900 degrees F which means that the sulfuric acid rain that falls never reaches the surface because it evaporates on the way down.
the only plausibly survivable (even by extremophiles) regions are 50-65k above surface and active biology has a big effect on both atmosphere and climate.
there exists no verified proof of life there, now or ever.
the surface is about 1 bn years old and has no signs of liquid water having ever existed. many scientists have posited that it once did, but this is, best i can tell, entirely speculative and based on circulation model simulations.
using the same tools/models that have evidenced near zero predictive value on earth on decadal scale (GISS is a top climate modeler/AGW proponent) to model what venus COULD have been like billions of years ago represents pretty thin gruel to serve up a meal as spicy as “venus was once like earth today and earth will wind up like venus if we’re not careful.”
this is especially so because venus is decidedly non-earth like on a VERY important dimension: venus has no magnetic field.
(fun fact, we don’t really know why. it has an iron core, like earth. there really is an astonishing amount about these basic issues we don’t understand.)
it therefore lacks the protective shield enjoyed by earth which prevents lighter gasses from being cracked loose and eroded/blown out into space by the solar radiation and solar wind when it pummels the atmosphere. (source: NASA)
this, in conjunction with 1000’s of active volcanoes has driven the climate on venus and removed nearly all water (assuming it ever had much) and, perhaps more importantly, the water cycle from the planet.
so, poor venus never really had a chance and the idea that it once had a habitable climate much less was some sort of “climate change that could happen here” appears fanciful.
water molecules would have been cleaved by high UV due to solar proximity and lack of strong magnetosphere. and all the hydrogen would have been blown off in the induced magnetotail preventing water from reforming.
whether venus ever existed in a goldilocks zone (cool enough for liquid state water not to boil, warm enough for it not to freeze) is simply not known. the sun was once 25-30% dimmer, but just what that meant given what was likely much lower albedo is just not predictable with any confidence.
this is all presumptive modeling that lacks any basis in observational evidence whatsoever and the vastly more solar energy, lack of a magnetic field, incredibly slow/locked spin (daytime lasts around 2 months), and the lack of known plate tectonics make venus so different from earth that “models” claiming it once had oceans are surmise, not evidentiary.
regardless, temperatures and pressures are unlikely to have very looked anything like todays earth. one can have oceans at high temps if pressure is high enough. at 93 bar, water boils at ~575 F. but we’re not talking about “summer in arizona” there. we’re talking about “your oven dial doesn’t go up that high.”
liquid water and a water vapor cycle are the great drivers of moderate climate. it holds heat at night and traps heat in the atmosphere making for stable, constant temperatures. water vapor, not CO2 is by far the dominant “greenhouse gas.” without water vapor, earth climate would collapse and we’d be an iceball and without oceans as a heat sink, earth would be colder and temperatures far more varied.
this is also VERY different from venus and almost certainly a direct effect of our magnetic field and planetary positioning as well as our plate tectonics. those don’t change much.
they all engender stability.
but here is where this starts to get interesting:
because while venus may never have been earth like, earth was once decidedly venus like.
multi-cellular life on earth began about 500 million years ago, but earth has been here far longer. the hadean period spanned the period from 4.6bn to 4bn years ago. we still have some rocks that date back this far and studies of zircons show liquid water on earth 4.4bn years ago despite surface temperatures around 450 degrees F. this was possible because of immense atmospheric pressures in the 100 bar range. (100x present, higher than venus is now) earth may have even had sulfuric acid clouds.
bottom line, hadean earth sucked. you didn’t want to live there. probably, nothing did.
it was a very inhospitable place until about 4bn years ago when a combo of oceans and plate tectonics began removing the over abundance of CO2 and sulfur from the atmosphere concentrating most of both into rocks. not tundra or oil. actual rocks. that’s the huge carbon sink on earth.
so, ironically, geology and magnetics conspired to make earth edenic and life supporting.
the great climate change was a move from a planet where tin would melt if you left it outside to climates a lot like today.
getting to keep your light gasses and liquid water is a wonderful thing.
ah, but what if this sinister CO2 were to return? might not we revert to venus?
this seems deeply implausible for a variety of reasons, foremost that we now have abundant liquid water and a strong water cycle.
the second reason is that CO2 is now scarce on earth and will remain so.
interestingly, before first CO2 driven global cooling and later CO2 driven global warming became prominent fears, many spoke of our current “CO2 impoverished state” and fretted that if it got much lower, we’d have mass planetary plant die offs. (under about 200ppm CO2, most plants struggle to achieve sufficient photosynthesis. under 100-150, we’d be in serious trouble)
carbon dioxide is plant food. unlike brawndo, it really is what plants carve.
this is why it’s used in commercial greenhouses which run at 2-3X atmospheric content.
this is still discussed, even by the folks warning of AGW.
“Results showed that carbon dioxide fertilization explains 70 percent of the greening effect, said co-author Ranga Myneni, a professor in the Department of Earth and Environment at Boston University. “The second most important driver is nitrogen, at 9 percent. So we see what an outsized role CO2 plays in this process.”
and current levels are, by past standards, very low at about 420 parts per million.
the cambrian was nearly 20 times that and brontosaurs ate giant plants growing at nearly 7X the CO2 of today.
the hadean when earth was going through its “i identify as venus like” phase, was probably 1,000 to 10,000X higher than even peak cambrian.
none of these are plausible ballparks to recur barring impact with a body sizable enough to vaporize a large percentage of earth’s crust and at that point, warming would be the least of our worries.
earth CO2 has risen by about 100ppm in the last 60 years.
at these rates, it would take 350 years to reach 1000, a number still very low by historical standards and that did not generate runaway behavior in the past.
so it would seem we have quite a lot of safety margin here before anyone has to worry about earth becoming venus 2.0 and like maybe the WEF should give it a rest on this one.
this is not a serious addition to the discussion of climate.
it’s a fine scare story, but lacking in foundation.
venus has twice the energy in per m2 coming in, 223,000X the CO2, and 93X the pressure of earth while lacking liquid water, active tectonics, and a protective magnetic field.
they are nothing alike with regard to atmospheric and climate expectation.
earth escaped being venus and found an equilibrium so profound that global temps for 500 million years have varied less than most places vary winter to summer or even day to night despite major perturbations and continental realignment (which now favors “cool” given a polar continent and the closure of the isthmus of panama blocking equatorial mingling of the great oceans.)
claiming the bright shining “morning star” is somehow an analogue to predict imminent earth tipping points when we have already had 20X stress tests that failed to cause runaway warming is just not going to pass muster.
leave the planetary campfire stories for the cubscouts.
they have no place in public policy.