When we think of global warming, we think of things really sucking: rising oceans, catostrophic new weather patterns, disrupted food supply chains, Alaskan beach resorts. It’s all awful and very likely to happen, for global warming to hit its current worst case scenario. Because people are still pretty much idiots. Civilizations will reach concensus about climate change and science maybe actually being right about this too late to fix anything and. . . it’ll suck. You, or at least your offspring, will wind up a coastal refugee suffering through alternating droughts and epic, hand-of-god hurricane seasons. Meanwhile, the changing climate will cause a massive redistribution of food and water resources, leading to sustained global war. It’ll be brutal, but it won’t be as bad as the true worst case sceneario: runaway global warming, e.g. Venus syndrome.
Venus syndrome refers to the speculated early history of Venus, where trapped greenhouse gases created a positive feedback loop eventually boiling away the planet’s oceans and leaving it a miasmic 460°C hell featuring an almost entirely carbon dioxide atmosphere with a sheet of sulfur dioxide clouds on top. In terms of future inhabtability and life in general, Venus syndrome would be a bit more like sustained global nuclear war than much of what we imagine happening in our current climate change scheme.
Yesterday, Colin Goldblatt at the University of Victoria in Canada and Andrew Watson at the University of East Anglia in the UK, published a paper at the arXiv.com pre-print clearinghouse — via the brave arxiv.com crawlers at Technology Review — reassuring that runaway global warming is probably not going to happen on Earth. “The good news is that almost all lines of evidence lead us to believe that is unlikely to be possible, even in principle, to trigger full a runaway greenhouse by addition of non-condensible greenhouse gases such as carbon dioxide to the atmosphere,” they write.
But, at the same time, we can’t rule it out because we don’t totally know “the dynamics, thermodynamics, radiative transfer and cloud physics of hot and steamy atmospheres.” We have a lot of climate science as it pertains to global warming nailed to the wall, but the relationships that could lead to something like Venus syndrome on Earth aren’t very well known. We need more information.
The worry is that increasing water vapor from heating oceans will heat the atmosphere even more, leading to more evaporation in a positive feedback loop. As the atmosphere gets more and more swampy, the less thermal radiation it can emit into space. The less radiation it can emit, the warmer the planet gets and the more the oceans evaporate, making things yet warmer still while, at the same time, weakening the planet’s ability to cool itself.
So maybe you’re thinking that this all stops when the ice caps melt and cool off the oceans or we decide to stop polluting but, no, it’s too late. The cycle continues until we cook the atmosphere to 1400°C, at which point heat can radiate away at wavelengths not blockable by water vapor. In any case, that’s hot enough to boil away the oceans and we’ll all be dead. And then some aliens will find Earth some years later and wonder just what in the hell happened. A couple of alien scientists will publish a paper to a website that will get largely ignored, wondering if what happened on Earth could happen to their planet. And so on.
There are solutions. In the case of runaway global warming, we could build giant reflective shields to act as a kind of global sunblock, or maybe we could even screw around with Earth’s orbit, pushing the planet into cooler territory. In any case, it may be of some comfort that all of this boiling and roasting is going to happen on Earth anyhow in a couple million years when the sun naturally gets brighter.
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