Like all informed humans, and especially all informed parents of beloved children, I am deeply concerned about the future of our planet. But there’s one thing about climate change that confuses the heck out of me; help me out Dopers?
The primary temperature control on our planet comes from water. Huge masses of it in the oceans respond fairly quickly (that is, “quick” from a geologic perspective) to changes in temperature. This process is accelerated by the water’s movement and mixing through the tidal force supplied by our moon. So far so good.
Another constant process is the rain cycle. Water from the ocean is constantly evaporating up into clouds, which partially block sunlight from reaching our planet, until they are interrupted by a cold current, which causes the droplets to fall down as rain on the ground or water below. This has the added benefit of carrying a lot of the air pollution back down to the ground with it.
Some of these clouds rise very high indeed, into the cold, thin, high atmosphere, where they crystallize into ice. When a strong enough down-current (storm) affects these, they bring that ice down with them.
So, here’s my query: won’t we reach a point of climate change when the clouds will block so much of the sun that the process will turn itself around and the Earth will begin to cool again? Won’t those super high clouds increase to the point that less sunlight will sink into the atmosphere to heat us up? Won’t there be increased volatility in the upper atmosphere “carrying more cold”* down to ground level? I’m not saying that this will happen quickly, or that we humans won’t suffer for our folly in the mean time. But I never hear a word from climate scientists about how the Earth will naturally begin to re-assert balance, as it has always done in the past.
tldr: Won’t the air carry more and more water as temperatures rise? And won’t that eventually block sunlight to the point that temperatures will move back towards the old mean?
Please excuse my childish terminology, I’m not a climate scientist, and my knowledge of thermodynamics is only power-point deep. I’m here because I’m trying, so please be patient.
You outline the actual problem: Change. Initiating changes that cascade like that means all sorts of problems for people in different areas. Farming here takes a drought, but new land can be farmed over there. This land is dry now, then under water, but other land is now dry. This area was good for these species, but this area has changed. And wait, now it’s all changing back on a geological scale (yay planet), but the geological scale means most life is overwritten with new life after everything settles.
Disruption to all species is the problem as all the changes you outlined take place. So, we doom most current species; the planet reacts and swings back, but what lives on and what is gone is a wildcard. How many people die… or how many people thrive as a result? Is the planet more suited, less suited or not suited to intelligent life or life at all.
The change aspect introduces a wild card so unknown and risky (unpredictable) we seek to avoid the planet dumping water into oceans, changing landscapes, currents, climate, jet streams, etc. Sure, it probably will swing back, but we’re interested in deferring anything that causes the swing and probable swing back. If we have 1 million years on this earth, the change along might cut that in half.
If we say that we are 100% sure the planet will counter punch the changes we’re initiating, the act of changing will probably doom us to not even see the counter punch.
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You forgot the fact that those clouds hold in heat far more than clear skies.
More and thicker winter clouds with higher tops trap heat better. This is actually why snow is rare in places like Seattle where freezes tend to happen during clear winter days.
Here is a page that may help explain why you get warmer with more frequent and more intense storms with more cloud cover and do not gain the cooling advantage that you are asking about.
Increased cloud cover means increased reflection to space, yes, but where do you get the idea this would lead to a cooling trend and not just be a new equilibrium point?
The height isn’t all that important. Clouds reflect a lot of sunlight directly, and that sunlight is already in the window that our atmosphere is the most transparent in.
No. Sure, a droplet of water radiating heat at altitude will send more of it to space, but it will also be blocking radiation from the ground.
That’s because your assumptions are wrong. The Earth might naturally re-assert a balance, but that could be at several degrees above what we like. There’s no reason to assume a “clouds will swing us back to our norm”.
Feedback loops are probably not strong enough to move us to conditions like Venus, but unless we bring the CO2-levels down temperature is going to rise to a new norm over a few centuries, and stay there.
I have a question: will increased temperatures per se, in the absence of otherwise higher global relative humidity, increase cloud cover? Because while the air will hold more water when warm, it wouldn’t form more clouds unless the answer to my question is “yes”.
And the average global relative humidity will only depend on the unpredictable nature of the change as others have mentioned: it won’t predictably rise, because the atmosphere already holds almost as much water as it feasibly can given the weather cycle of evaporation followed by rising air followed by rain. If those patterns change, giving us more arid areas and fewer wetter areas or vice versa, we could have more cloud coverage - or less.
By “transparent” are you referring to the high-levels like UV that pass right through the clouds? Would those be affected at all? Do they convert into heat when they hit water or other materials?
Surely a ray of infrared reflected back out toward space by a ground level cloud leaves behind more heat as it travels than a ray reflected back from the stratosphere?
Most of the energy in sunlight is in visible light, not the infrared. The atmosphere (when there are no clouds) is highly transparent to visible light, so very little sunlight is absorbed by the atmosphere. Mostly, sunlight goes right through the atmosphere until it hits a liquid or solid surface. When it’s reflected by a cloud, the reflected light is still visible light, and it will go right through the atmosphere again.
But as others said, it’s a complex issue. The ground emits infrared radiation; if there are clouds above, the infrared is absorbed by the clouds, and much of the energy is re-emitted back towards the ground. But when the sky is clear, the infrared goes straight out into space. Which is why clear nights are generally colder than cloudy nights.
UV and visible light. It doesn’t turn pitch black even with complete cloud cover. And yes, any radiation that isn’t straight up reflected is absorbed and heat up whatever they hit.
Reflected light has the same wavelength as the incoming light. Most of the energy emitted from the sun is in the visible and near infrared spectrum, and most of that easily passes through the atmosphere, so high level clouds will not do all that much better at shielding us from heat than low level ones.
My non-meteorologist hunch is also that high altitude clouds are wispy things that let a lot of light through and that there is no way for them to be like a thick stormcloud that darkens the sky.
Clouds are great at stopping far infrared heat radiation from the ground though, which is why clear nights are really cold, and cloudy days are cool rather than cold.
There are all sorts of feedback mechanisms involved in climate, some positive, and some negative. Even just atmospheric water includes both sorts: Clouds reflect light, and so have a cooling influence, but water vapor is a greenhouse gas, and so has a warming influence. No matter what we humans do to the atmosphere, eventually it’ll get to a point where the negative feedbacks dominate and so we’ll reach a new equilibrium, but there’s a lot of work that goes into figuring out where that equilibrium would be, and as our influence is constantly changing (by adding more and more CO[sub]2[/sub]), the equilibrium point is also constantly changing.
IM not a climate guy but have good experience modeling flames ( industry burners, gas turbines, chemical reactors, etc.) where thermal radiation absorption properties of H2O and CO2 come into play.
While both CO2 and H2O are greenhouse gases and they both absorb radiation reflected off earth, the CO2 molecule is special. CO2 is actually not as good as H2O when it comes to the percentage of radiation absorbed. The special property of CO2 is this : it absorbs radiation in the 12-15 micrometer range whereas H2O is virtually transparent in this range.
The 12-15 micrometer range was/is the window through which earth lost (radiated) it’s heat to space which is getting progressively closed.
The part I bolded above is also important, and actually bad news. With water, it takes very little to completely block infrared in certain wavelengths. If it’s already completely opaque, adding more water doesn’t make it any more opaque.
But CO2 isn’t like that. Even in the 12-15 um range, the atmosphere isn’t completely opaque. Which means if you add more CO2, it does become more opaque. Raising CO2 concentration from 300ppm to 400ppm does make a difference in how much infrared radiation makes it out through the atmosphere.