Hacker News Reader

Comment by fallingfrog | Hacker News Reader

I think one thing that everyone should know with respect to climate change is how simple it is to prove that increases in co2 cause increases in temperature. You can literally put some co2 and a thermometer in a bottle and watch the temperature climb. It’s not some mysterious effect.

View on HN

Your claim is that if you put CO2, a relatively easy to acquire gas, into a bottle, the temperature will keep climbing? Isn't this a violation of the laws of thermodynamics.

I'm not so sure your experiment would work unless you specify various other conditions. The main reason that CO2 is a 'greenhouse gas' is that it absorbs thermal infrared light. In other words, CO2 'reflects' infrared light. This, combined with the fact that the sun is continuously heating the earth means that -- in the context of the Earth's atmosphere -- CO2 acts like a giant blanket. Only in the context of a continuously externally heated object does CO2 cause temperature increases, which is not something that is necessarily going to be simulated by 'putting CO2 into a bottle'.

However, CO2 by itself does not cause things to heat up. That is patently ridiculous, and bad science. In fact, if you fill a jar with CO2 and water gas (also a greenhouse gas), and expose it to the air on a cloudless night, and then put some kind of insulating layer between it and the earth (like some feet of straw), it'll actually freeze: https://pazhayathu.blogspot.com/2012/02/water-cooler-air-con...

https://youtu.be/Ge0jhYDcazY

This is a video demonstration. All you need is 2 bottles under the same amount of illumination with different amounts of co2.

Sorry, I should have said, under illumination, and the temperature will reach a higher equilibrium with co2 in it, but it will not rise without limit.

I guess the previous poster was assuming the experiment taking place under a suitable light source like a halogene lamp, so the effect of CO2 in the atmosphere can be reproduced.

But there's more than that... you'd also need a body of large thermal mass opposite the halogen bulb to absorb the heat, and then re radiate it, so it could bounce off the CO2.

I was thinking of a 12" glass sphere with an 11.5" black sphere inside of it. The black sphere would be the thermal mass (maybe full of water) and it would have temperature sensors all around. Then in the space between, some air. Get a baseline temperature reading. Then pump in a tiny amount of CO2. Check temperature delta.

I wonder if something like that has been done.

The amount of change you would see from that is going to be really way too small to get an accurate reading on. You'd also need to run a control experiment with heating the ball with just plain air (rather than air + extra CO2), because the glass is also going to act like a greenhouse trap anyway.

This misses the actual mechanism, which is not as simple as you might think. CO2 at ground level is actually irrelevant. What matters is CO2 at the height in the atmosphere where an infrared photon might escape to space without further interactions with the atmosphere. Increases in CO2 matter only because with more CO2 the height where a photon might escape increases, and the air is colder at this increased height, and hence the amount of energy emitted is (temporarily) less - until the overall temperature of the earth increase so that the temperature at this increased height is back to what it was before.

I don’t think it quite works that way- infrared radiation emitted from the ground can exit directly into outer space.

That's true for infrared radiation of a frequency that isn't absorbed by CO2 (or other greenhouse gasses). But a photon at a CO2 absorbtion frequency makes it only a few feet at ground level before being absorbed again.

The central dispute is not whether CO2 causes a greenhouse effect. It's that CO2 is itself a relatively weak greenhouse gas, compared to say methane (making cow farts a valid concern), and our atmosphere is already relatively saturated. The dispute is whether increases in the amount of CO2 affect other climate systems that work together to magnify the warming, and that requires computer modelling.

So far the spherical cow model of climate change that Arrhenius used, with better numbers for absorption spectra and so forth, have historically out performed computer models without disagreeing with them by a huge amount. We can hope that the most recent computer models are more accurate but we won't know quickly. You do need to model that CO2, while weak, blocks a spectrum of infrared that isn't blocked by the much more influential water vapor. But that still doesn't require looking at feedback loops, much less cell modeling.

To be honest that uncertainty about exactly how things will turn out is what makes me most concerned about global warming. Better to play Russian roulette with 6 blanks that'll ruin the hearing in one ear than with 4 blanks, one entirely empty chamber, and one actual bullet. IPCC forecasts are bad but they're not unbearably bad. The real danger is that thing'll go far worse even if we can also plausibly hope that they'll be far better.

Cow belches. But it turns out that extractors have been massively under-reporting their own belches. Anyway when the frozen polar methane bubbles (i.e., explodes) out, and the permafrost melts and decomposes, cows will be the least of our problems.

The simple example I gave can’t give you any sort of quantitative answer as far as how much the earth will warm, as you pointed out the earth climate is a complex system with many feedbacks. But it’s an easy way to see the basic principle.

Sounds simple but it would be hard to get an accurate test. I mean, it's not a basic kitchen experiment, is it? And why is it that modifying such a small part of the atmosphere (0.04%) can cause such a huge problem?

> And why is it that modifying such a small part of the atmosphere (0.04%) can cause such a huge problem?

There's a lot of energy going by, and greenhouse gasses grab a slice of it that is otherwise poorly grabbed.

Perhaps picture a small cabin, with a big hot stove, and a window open to bitter arctic night. Without the window, you soon bake. Without the stove, you soon freeze. You tweak the window's openness to change room temperature. Keeping or killing your house plants as you prefer. The window is a patchwork, some patches overlapping, some not. The part of the window along the ceiling matters a lot, as much heat is trying to escape there. Tweak a patch over an otherwise open hole there, and it matters.

Earth is doing a BBQ roll, hanging between white hot Sun, and black cryo space. The atmosphere fluffs out during the day, and contracts at night. Lunar day is 120-ish C. If aliens umbrellaed the Earth, then vacuum would come down to ground, the atmosphere become some meters of oxygen nitrogen snow. That's a large flow of energy going by. Atmospheric water absorbs, and emits back, a lot of heat - deserts get cold at night. Different molecules have different absorption spectra. CO2 absorbs well at some frequencies water doesn't. Including in thermal infrared, where ground is radiating heat to space.

As an aside, Stanford has a fun project for more efficient refrigeration. A material engineered to preferentially emit heat, thermal infrared, at frequencies less well absorbed by the atmosphere. The "holes". So just sitting on a roof, it's cooler than the roof, because it can better "see" space than the roof can.

It's a simple lab proof of carbon dioxide causing heating. We're not discussing a scale model of the sun and earth.

The same reason an extra pinch of salt can ruin a soup.

It is indeed a basic kitchen experiment.

https://youtu.be/Ge0jhYDcazY

https://youtu.be/kwtt51gvaJQ

> And why is it that modifying such a small part of the atmosphere (0.04%) can cause such a huge problem?

The modification is invisible to you, but not invisible to the photons which are supposed to leave the atmosphere and cool off the earth a bit. It it were visible to you, it would look like this:

https://www.youtube.com/watch?v=81FHVrXgzuA

Regarding the photons of thermal frequencies leaving the Earth atmosphere, or remaining there, the simplest you can imagine is a blanket: if it's cold outside the blanket keeps the heat not leaving the area under the blanket, keeping you warm. Here, the CO2 is actually a "one-way" blanket, it doesn't block the incoming radiation:

The heat coming from Sun has other frequencies as it comes than the photons blocked that would cool off the Earth.

The key is: CO2 is an ink-black "blanket" for exactly a part of the radiation that cools off the Earth. It's not too big, but big enough to make in sum that 0.8 C degree change since 1880. Or to produce even more warming in the coming years as we burn always more and we haven't managed to change that.

A little more precise:

"Energy arrives from the sun in the form of visible light and ultraviolet radiation. The Earth then emits some of this energy as infrared radiation. Greenhouse gases in the atmosphere 'capture' some of this heat, then re-emit it in all directions - including back to the Earth's surface."

(There's of course infrared radiation coming from the Sun, but the one making problem is the radiation from the Earth)

Scientific details, like absorption spectra and the measurements, are here: https://skepticalscience.com/print.php?r=35

A little simpler explanation by American Chemical Society:

https://www.acs.org/content/acs/en/climatescience/climatesci...

Or even, for kids, "meet Mr. Sunbeam" part from Futurama:

https://www.youtube.com/watch?v=0SYpUSjSgFg

It doesn't. The atmosphere is not a closed system as upper limit varies. The global temperature strongly correlates to the sun's activity and our distance from it, and nearly not at all to anything else, other than cataclysmic events such as huge volcanoes, asteroid strikes, etc.

Not true. Very short term effects correlate to solar exposure, where CO2 effects have a built-in long-term filtering that stretches out the response time, averaging out shorter fluctuations.

Temperature is increasing not because of increased insolation, but because of increased retention.

It's almost as if CO2 is a sort of "greenhouse" gas!

Reply on news.ycombinator.com