Putting the life back in science fiction

The Blue Sky Tipping Point
February 25, 2019, 10:49 pm
Filed under: Altithermal, climate change, deep time, Hot Earth Dreams, Uncategorized | Tags: , ,

Got some new climate science to talk about, yay! Actually, it’s not good news, but it is fairly solid model evidence for tipping point, up around 1200 ppm CO2 in the atmosphere (as I write this, we’re around 410.81 ppm).

The cause of the tipping point is that around 1,200 ppm, stratocumulus clouds may go away.  Clouds blanket around two-thirds of the planet on any given day, and low, puffy stratocumulus are among the most common.  Without clouds, the albedo of the planet drops precipitously, because water and land are darker (have lower albedo) than nice white, fluffy clouds.  That means more sunlight hits the oceans and lands, that heat is absorbed and reradiated, and the planet could heat up by an additional 8oC, in addition to the 4oC that models predict would occur with 1200 ppm CO2.

This finding, if confirmed, puts modern-day climate models more in accord with what happened in the Paleocene-Eocene Thermal Maximum (PETM).  We know what the CO2 concentrations were back then from fossil evidence, and we know how hot it got from some geological proxies.  But we couldn’t get that amount of CO2 to produce that amount of heating using modern models, because these models have baked-in assumptions that clouds will be present and affecting albedo.  The loss of clouds would bridge the gap between fossil evidence and the models, meaning that the paleoclimatic record is in accord with this new modeling work.  To be clear, the loss of stratocumulus during the Paleocene didn’t cause the PETM.  It’s just that current climate models assume clouds, and if there were none to begin with (presumably true in the Paleocene), then the world would have started in a different place.

Even more interestingly, there’s apparently a hysteresis effect with the blue sky tipping point.  Once the atmosphere’s switched to fewer-stratocumulus clouds mode, it will tend to stay that way, in a self-reinforcing feedback look, until CO2 levels fall to around 400 ppm, where we are now, or even lower, at which point stratocumulus can form again.  This also accords with the fossil record.  The Pliocene, which had atmospheric CO2 levels around 400 ppm, was 4oC hotter than the world we live in now.  However, it had come off a very hot Tertiary period (the Paleogene and Neogene) and was cooling down.  The formation of stratocumulus clouds may have coincided with the onset of wide-scale glaciation in the late Pliocene, with worldwide glaciation growing with the Pleistocene starting 2.58 million years ago.  Yes, modern humans are children of the ice age, as the book had it, but we might be children of the clouds, too, especially those of us with lighter skins.

Now, we shouldn’t get too excited yet about when the clouds go away.  We’re predicted to hit 1200 ppm around 2100 CE, following a business as usual emissions model, so there’s actually a fair amount of time for us not to hit 1200 ppm, either by nuclear war (yes, politics still matters), petroleum-based civilization falling apart due to the stresses of living on a planet with over 350 ppm of CO2 in the air, or conversion to 100% renewable electricity powering our civilization, with or without nuclear power.   It is likely that no one reading this will live to see the blue sky tipping point either.  And there is the complexity that no one’s modeled the coupling of stratocumulus cloud formation (which is impossible to model in a global climate model) and  global winds (which are already globally modeled), and there’s some evidence that these interact to make the clouds a bit more robust.

Caveats aside, I think this model’s onto something, and so do a bunch of climatologists, apparently.  So if you want to imagine a severely climate changed world, I’d suggest imagining a clear blue sky, with perhaps a few wispy high clouds.  Storms will come, but general overcast and fog?  Not so much, at least when the sun’s up.  That’s how you get gators in Greenland.



4 Comments so far
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I suppose there is good news in this.

1. 1200ppm is quite far off.
2. Geoengineering with artificial clouds might stave of the tipping point.

Clutching at straws, I know, but any ray of light…

Comment by Alex Tolley

I should note that the timeline for hitting 1200 ppm CO2 in the atmosphere is based on the assumption that humans will directly emit the gas.

The thing to be concerned about is the ~1400 gigatons of CO2 and equivalents (e.g. methane) sitting in the Arctic permafrost. If that stuff rapidly mobilizes, we could easily blow to 1200 ppm equivalent before 2100. Remember, methane is a more potent greenhouse gas.

Comment by Heteromeles

I’d like to see this phenomenon examined together with the strength of storms in terms of wind speed and water volume lifted up and then dumped down to see if and how they might be related because this winter is one of the worst that I can remember.

Alex: ‘any ray of sunshine’ … Like this adage, human civilization will go from representing ‘hope’ to ‘despair’.

Comment by SFreader

While I am not as negative on the likely outcome as our host, I am pretty worried about the disruption the changing weather patterns with climate warming is bringing. Even here in California, where I live in teh Central Valley, the politics is still about getting as much water to farmers as possible, with little concern about the environm4ent. Farmers are gonna farm until the last drop has gone. Almond orchards are still being planted despite this appallingly wasteful use of [mostly aquifer] water. There is no discussion about finding alternatives for land use. It is business as usual. Our senior senator, Feinstein is not at all on board with teh Green New Deal, which is just climate denialism under the old (and increasingly dysfunctional?) “politics is the art of the possible” mantra.

From what I follow of the politics of Britain, it is much the same, only there the problem is mostly about energy sources, rather than farming, although Brexit is causing a bit of a stir on farming economics.

Right-wing governments are emphasizing economic development over environmental issues, with Brazil the most egregious example. China is pouring concrete as fast as it can.

So rays of light are all that I can see so far. I’m not there with James Lovelock that we are definitely screwed, but…

Comment by alexandertolley

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