[thrw_skpt]

I guess I skipped one or two steps in my mea culpa, so I'll cover them here.

You posted this link https://www.skepticalscience.com/co2-residence-time.htm

In this link, after a short introduction, we learn that there are about 750 GT of CO2 in the atmosphere, and about 200GT enter and leave the atmosphere each year, which is about 27%. CO2 molecules are indistinguishable from one another (leaving aside the trace amounts of molecules that contains isotopes different from C12 and O16). A molecule produced by human emissions does not look in any way different from another CO2 molecule. Moreover, in no time all the anthropogenic CO2 is equally mixed in the rest of the CO2 (by diffusion). Because of that the proportion of CO2 that stays in the atmosphere for a given time follows an exponential law with a decay coefficient of -log(1-0.27)=0.19 (see note). So out of all the CO2 in the atmosphere at a given time, only 83% stays there for 1 year, only 15% for 10 (uninterrupted) years, and only 5.6*10^(-9) after 100 years. And this is true both for all the original CO2 as for the anthropogenic CO2.

Now, if you change the definition of what it means for CO2 to remain in the atmosphere, then you get the long life you mentioned, but you do need to change that definition.

And this has nothing to do with averages vs medians or percentiles or other statistical concepts (which by the way, I am very familiar with).

(note) I'm skipping another step there, how to go from indistinguishability of CO2 to the exponential law, but if you want me, I can fill that in too.

[Cretin2]

Anthropogenic CO2. I thought that was apparent. Naturally emitted CO2 emissions are relatively constant and balanced over the last several hundred years, anthropogenic CO2 is not. Therefore as we continue to produce excess CO2 which cannot be absorbed by the system it results in excess CO2 which is not removed for upwards of 1000 years. We're removing sequestered CO2 and putting it in the atmosphere. It's not that complex.

From the same article I posted and you referenced:

"Dissolution of CO2 into the oceans is fast but the problem is that the top of the ocean is “getting full” and the bottleneck is thus the transfer of carbon from surface waters to the deep ocean. This transfer largely occurs by the slow ocean basin circulation and turn over (*3). This turnover takes 500-1000ish years. Therefore a time scale for CO2 warming potential out as far as 500 years is entirely reasonable."

You stated: "Because of that the proportion of CO2 that stays in the atmosphere for a given time follows an exponential law with a decay coefficient of -log(1-0.27)=0.19" this was not in the article. You're applying equations which are not appropriate to the system.

To repeat: https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Cha... rather than make up equations and argue with me about the minutia you really need to take some time and understand the physical science basis as explained by experts.

Within a thousand years, the remaining atmospheric fraction of the CO2 emissions (see Section 6.3.2.4) is between 15 and 40%, depending on the amount of carbon released (Archer et al., 2009b).

Again....I'd be interested to know what you're reading that brought you these arguments as they seem to be passed around circles of skeptics (not saying deniers).

[thrw_skpt]

> "You're applying equations which are not appropriate to the system."

Why are you saying this? Because it's not in the paper you linked? Are you sure that equation is not appropriate, and if so, because you know of an argument, or because you believe some expert?

On my side, I'm not reading things that circulate in some "circles". I'm just a guy who's curious about climate change, but who is not an expert. But I have a strong math and science background, and I can follow pretty much any scientific argument.

That being said, I'm faced with this conundrum: supposedly 97% of experts agree on a topic. The result of their agreement happens to be the result that brings in more funding for their research. There is an obvious conflict of interests. But this conflict in itself doesn't mean the consensus is wrong.

So, I'm trying to inform myself and reach a conclusion. I use both scientific reasoning and non-scientific heuristics.

Non-scientific heuristics are like this: Nate Silver (the guy behind the 538 blog) explains how he used statistics to get to the conclusion that climate change is real and is caused by the anthropogenic CO2. This sways me a bit towards believing the consensus. Freeman Dyson says the models fail to capture clouds. This sways me a bit in the opposite direction.

As for the scientific reasoning, it goes something like this. I get the general idea about CO2 absorbing the infrared radiation coming from the ground and therefore trapping some extra heat in the atmosphere. But CO2 is only 400 ppm, it's a very tiny part of the mass of the atmosphere. The youtube videos that you see with a bottle full of air and a bottle full of CO2 and how they heat up under a lamp are not very relevant. In the real world we are talking about an increase from 250 ppm to 400 ppm, not from 250 ppm to 100%. So the argument needs to be a bit more complex, and the IPCC report goes in more details. Following the details shows me they are thoughtful, and it's not junk science, so it swings me a bit towards the consensus.

But something is missing. Maybe you can fill it in, considering that you read a lot about these things. And it would honestly be appreciated (and by the way, you seem to be quite prejudiced against me, please give me a bit of benefit of the doubt).

Here's what's missing (imho). Bear with me, the story is a bit long. We are fortunate to live in a world with a lot of water. Water is special for a lot of reasons, but one absolutely remarkable property of water is that its specific heat exceeds by leaps and bounds the specific heat of any other substance that shows up in any abundance in our environment (e.g. at room temperature you need 4.2 Joules to warm up 1g of water by 1 deg Celsius, only 2.4 J for 1g of ethanol, and 1.0, 0.9 and 0.8 for air, O2 and CO2 respectively). But the truly astonishing number is the specific latent heat of vaporization for water, which is 2265 J/g. This exceeds any other specific latent heat for any other substance for any phase change by a very large amount (on a tangent note, this is what allows warm-bodied animals to keep their temperature constant, or put it another way, without this little curious property of water, humans would not exist).

There are about 750 GT of CO2 in the atmosphere (all gaseous) and about 13000 GT of water (both liquid and gas). Now the typical energy balance equation described in the IPCC report tells you how this water absorbs and re-emits radiation and in what spectrum and in what amount. But the missing piece is this: by far most of the radiation is absorbed and released by water upon the change of phase, i.e. when it evaporates from the oceans and then when it condenses in the clouds (before it falls downs as rains). When the water condenses in the clouds it must release that tremendous amount of energy I mentioned above (2.2 kJ per gram). It can do that in 2 ways: it heats the surrounding atmosphere (but that can't absorb much because of the other constants I mentioned, the 1.0 J/g/K for air, which is a puny number applied to a very rarefied substance) or it radiates. From the radiation, half points down, but half points up, towards space. To me this way of releasing energy in space should be by far and away the main way of the planet to get rid of extra heat.

Can you point me in the IPCC report where this heat enters in the heat balance of the atmosphere? I looked for it, and I didn't find it.

(PS I didn't read this thing anywhere, it's my own thinking)

[Cretin2]

I love how interested you are in this and your desire to work this out from first principles. I say the equation is not appropriate for the same reason we're having this discussion on the residence time of CO2, particularly anthropogenic. It doesn't account for multiple processes and time scales. The IPCC uses the Bern Model discussed here:

http://euanmearns.com/the-half-life-of-co2-in-earths-atmosph...

Frankly I don't care about the 97% agreement. I'm sure it is just as high if not higher in terms of biologists agreeing that evolution is occurring. It's a talking point to get people with no scientific training on board. Unfortunately it has the opposite result in many cases since it's a weak argument from authority.

Excellent point about water vapor particularly when it precipitates and release energy during the phase change. I'm on mobile so not as good at finding things, here's some information from AR4 with sources, AR5 may go into more detail:

https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9s9-5...

9.5.4.2.1 Detection of external influence on precipitation

Mitchell et al. (1987) argue that global mean precipitation changes should be controlled primarily by the energy budget of the troposphere where the latent heat of condensation is balanced by radiative cooling. Warming the troposphere enhances the cooling rate, thereby increasing precipitation, but this may be partly offset by a decrease in the efficiency of radiative cooling due to an increase in atmospheric CO2 (Allen and Ingram, 2002; Yang et al., 2003; Lambert et al., 2004; Sugi and Yoshimura, 2004). This suggests that global mean precipitation should respond more to changes in shortwave forcing than CO2 forcing, since shortwave forcings, such as volcanic aerosol, alter the temperature of the troposphere without affecting the efficiency of radiative cooling. This is consistent with a simulated decrease in precipitation following large volcanic eruptions (Robock and Liu, 1994; Broccoli et al., 2003), and may explain why anthropogenic influence has not been detected in measurements of global land mean precipitation (Ziegler et al., 2003; Gillett et al., 2004b), although Lambert et al. (2004) urge caution in applying the energy budget argument to land-only data. Greenhouse-gas induced increases in global precipitation may have also been offset by decreases due to anthropogenic aerosols (Ramanathan et al., 2001).

Several studies have demonstrated that simulated land mean precipitation in climate model integrations including both natural and anthropogenic forcings is significantly correlated with that observed (Allen and Ingram, 2002; Gillett et al., 2004b; Lambert et al., 2004), thereby detecting external influence in observations of precipitation (see Section 8.3.1.2 for an evaluation of model-simulated precipitation). Lambert et al. (2005) examine precipitation changes in simulations of nine MMD 20C3M models including anthropogenic and natural forcing (Figure 9.18a), and find that the responses to combined anthropogenic and natural forcing simulated by five of the nine models are detectable in observed land mean precipitation (Figure 9.18a). Lambert et al. (2004) detect the response to shortwave forcing, but not longwave forcing, in land mean precipitation using HadCM3, and Gillett et al. (2004b) similarly detect the response to volcanic forcing using the PCM. Climate models appear to underestimate the variance of land mean precipitation compared to that observed (Gillett et al., 2004b; Lambert et al., 2004, 2005), but it is unclear whether this discrepancy results from an underestimated response to shortwave forcing (Gillett et al., 2004b), underestimated internal variability, errors in the observations, or a combination of these.

[Cretin2]

one more thing to add, here's a great resource for the IPCC data and methodologies: http://www.ipcc-data.org/

[thrw_skpt]

Thanks for the link, it's fascinating. I'll see if I can download some data and play with it to get a feel for it. As for the water vapor condensation, thanks for pointing me into the relevant part of the report, I'll take a closer look. At first sight, I like it that they paid attention to this issue, and I don't like that they didn't pay enough attention (a statement of the type "this may be offset by that" sounds a bit too cavalier to me). But it's a start. Back to the data and the transparency. This is really, really positive, it should go a long way towards assuaging the discomfort of climate skeptics (like me).