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Lower Thermal Radiation Input Needed To Trigger Planetary 'Runaway Greenhouse'
vinces99 writes with this excerpt from the UW news service: "It might be easier than previously thought for a planet to overheat into the scorchingly uninhabitable 'runaway greenhouse' stage, according to new research (abstract, article paywalled) by astronomers at the University of Washington and the University of Victoria. In the runaway greenhouse stage, a planet absorbs more solar energy than it can give off to retain equilibrium. As a result, the world overheats, boiling its oceans and filling its atmosphere with steam, which leaves the planet glowing-hot and forever uninhabitable, as Venus is now. One estimate of the inner edge of a star's 'habitable zone' is where the runaway greenhouse process begins. The habitable zone is that ring of space around a star that's just right for water to remain in liquid form on an orbiting rocky planet's surface, thus giving life a chance. Revisiting this classic planetary science scenario with new computer modeling, the astronomers found a lower thermal radiation threshold for the runaway greenhouse process, meaning that stage may be easier to initiate."
If correct, the habitable zone shrinks a bit and a few exoplanets might lose their potentially habitable status. And the Earth will leave the habitable zone in a billion and a half or so years as the Sun gets brighter.
I don't know about the rest of you, but I found the last two lines of the summary to be quite anticlimactic. Where's the fear-mongering?
I think mars was doomed from the beginning but I wonder if Venus could be terraformed with some kind of aerosol cloud to shade it and reduce the thermal input.
She was like chocolate when she drank... semi-sweet at first and then increasingly bitter.
What puzzles me is the absence of discussion of rain storms. These transfer a lot of heat to the upper atmosphere where it is radiated to space. They also pump energy into wind, increasing the circulation of air and increasing the heat loss from those convection effects.
Also, I gather the relative heating depends on the spectrum of the star to some degree. I gather there's some degree of transparency of water to the lower frequency UV so a bluer star with the same energy influx might have a bit more energy penetrate the atmosphere than a redder star.
The two are not linked. If we move off fossil fuels, our net CO2 emissions are cut to virtually zero, regardless of population (in fact, increased population acts as a carbon sink) or energy usage. Given enough cheap, carbon-free energy to distill seawater and power hydroponic stacks, we can support a far larger population if required.
Then all we have to worry about is excess waste heat, which will be a huge problem in 300-400 years. Though limiting ourselves to solar-derived energy can help a lot here.
Why would anyone engrave "Elbereth"?
Earth says: "I didn't leave the habitable zone. The habitable zone left me!"
If you think I voted for Trump because of this post, you're wrong. I voted for Dr. Jill Stein of the Green Party. Again.
That's why you put it "sunward" of the lagrangian point, so that it wants to fall into the sun, but is pushed out of the well by the solar wind. ;)
(Exactly where that would be depends on the specific impulse of the solar sail effect, and the mass of the reflector. Since both are hypothetical, I can't really give specifics.)
I can try to explain why. So far only known life form is our carbon based, situated exclusively on planet Earth - it includes every living organism on Earth, from amoeba to whale. We do not know it for sure, but it is possible (but unlikely) that it is the only life form existing in the universe. More likely is that life is like a sparkle in time in space - that there were (insert arbitrary large number) of life forms before us, and will be even more after us, but on cosmic time scale life expectancy of average life form is very small, so most of time/space is kinda lifeless and boring, and, most important of all, lacks an observer.
It's easy to think about observer as about god - it's something that everybody have or it lives inside everybody who's alive, it does not include any part of personality, it does not have any properties at all - so everybody have the same observer, or, you can say, it's one for everybody. If you think about it this way - it does not die after your death, so it makes you almost immortal - if you define 'me' such it does not include your personality, which I believe is right - as personality is just a sum of your genes and previous life experience.
So, what can be our purpose in life, and what can be the purpose of a humane race? Based on above I believe it should be protecting and expanding areal of carbon based life form. This runaway greenhouse scenario will end up with earth without liquid water on a surface - it can possible kill all life as we know it, so we should try to prevent it, even if it will happen after our personal deaths. Anyway, on a long enough time line, chances of survival of life on planet Earth drops to zero - so I believe we should do what we can to extend life, not necessary humans - maybe just a seeds from which evolution can begin - to as many planets as we can.