Would a doubling of CO2 include a CO2 feedback?

Question

Now my understanding, and I'm keeping this simple, is that if atmospheric CO2 was to double, we would expect to see a rise in the global average temperature of 3C; 1C directly from CO2 and another 2C from the balance of feed backs, this after equilibrium was reached. There is some uncertainty, but that is the best estimate.

But if there is warming, then wouldn't this mean extra CO2 as a result of out-gassing from the warming oceans? Wouldn't this then cause further warming and further out-gassing, this coupled process continuing until equilibrium is restored?

In case that's not clear, let me try this hypothetical situation; same planet but all other forcings are constant. Starting with the planet in radiative equilibrium, we release enough CO2 to double the amount in the atmosphere. The extra CO2 (with feedbacks) is now a forcing for a 3C rise in temperature but the rise is not instant; the oceans absorb much of the extra heat. Eventually, as the oceans warm, they will become net emitters of CO2, causing levels to rise over and above the initial doubling; this causing a cycle of further rises in both temperatures and CO2 levels, again, until equilibrium is regained.

As I said, I've kept that as simple as I can; please let me know if you think anything else is required. Now to my question.

What I am asking is, which of these two results would we see:

1 ) After the initial doubling, and allowing time to reach equilibrium, the planet is now 3C warmer but part of this warming is due to the warming from extra CO2 from the oceans. In other words, we have 3C of warming but from more than double the amount of CO2.

2 ) After the initial doubling, and allowing time to reach equilibrium, the planet is now more than 3C warmer; 3C from the initial doubling plus some additional warming due to the extra CO2 resulting from the first 3C? In other words, we have more than 3C of warming from the original doubling of CO2.

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If I can put it another way; exactly what do we mean when we say 3C from 2xCO2?

Or should the question be something like; how much anthropogenic CO2 will it take to double the concentration and cause a 3C rise?

Answer 1

I have linked a chart below so that people can see how the outgassing works.



The physics is this... CO2 is dissolved in seawater. More CO2 can be dissolved in cold water than warm water. So when the oceans warm, CO2 must be expelled from it and into the atmosphere.



So if you warm the ocean, the amount of CO2 in the atmosphere should rise due to the gas being released from the ocean (outgassed).



The chart looks at the annual change in ocean (surface) temperature, and the annual change in atmospheric CO2. Outgassing is evident if a rise in SST is followed by a rise in CO2.



If this years average SST is warmer than last years, then I expect to see that this years CO2 ppm is bigger than last years.



The chart has two series'

The first is the CHANGE in annual average Sea Surface Tempeature since the previous year. It is shown in solid blue.

The second is the CHANGE in CO2 ppm since the previous year. It is shown as a red line.



This is the chart.

http://farm9.staticflickr.com/8376/8409958899_114f77b2ac_b_d.jpg



As you look at the chart, look at the peaks in SST change. You will see that a peak in CO2 follows.



The graph is rather crude, and all I could knock up quickly, but it shows that outgassing does indeed happen in relation to change in SST.



The CO2 data is Mauna Loa: ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt

The SST data is the HadSST2 set: http://www.metoffice.gov.uk/hadobs/hadsst2/diagnostics/global/nh+sh/monthly



You will also notice that the annual CHANGE in CO2 has a slow rising trend in it. It goes up more than it goes down.



When the oceans cool again later on, CO2 is absorbed back into them... but not to the same level as before, it is a little higher. This rising trend is the anthropogenic portion of CO2 being added to the atmosphere.



I'll leave this here for a while for people to look at, and then answer the actual question.



Edit: 2 days later.

I’ve included a second chart (below), which is a bit better than the first in that it doesn’t hack the data into annual lumps, but handles them month-wise. Note that the “SST” used is the data from HadSST3, which is directly measured in ships’ water intake. It is not the actual surface as such (the top few microns), but the ocean temperature near the surface.



http://farm9.staticflickr.com/8367/8415656514_71df12df03_b_d.jpg



The root of this question is does warming of the ocean, and outgassing of CO2, have a positive feedback in the ocean? i.e. When the ocean outgasses CO2, does this cause further ocean warming leading to more ocean outgassing?



I don’t think so, and here’s why (all contrary thoughts to this and the following are most welcome, I’m not an expert on this).



The oceans are heated by direct SW insolation, not by downwelling radiation. (This is a big statement, is this correct?).



Solar radiation penetrates to about 10m in the ocean before being fully absorbed (50% in the top 2 metres). By contrast IR (downwelling) radiation barely penetrates beyond ocean surface at all... “Infrared radiation of the ocean comes from the top 10 microns of the surface “ http://podaac.jpl.nasa.gov/SeaSurfaceTemperature



The oceans are directly warmed by SW sunlight. Water is opaque to IR after 10 microns. The heating caused by IR is in the top few microns only, where it causes immediate evaporation, negating its warming effect. This is evaporation in addition to the evaporation due to the ocean temperature.



The water vapour is of course also a greenhouse gas, causing increased downwelling radiation, but the same applies there too... all this does is cause more evaporation at the very top surface, added to what evaporation is already happening due to the warming caused by the SW heating. What happens to all this water vapour?... it increases cloud... which shades the oceans, and cools them by blocking the SW light.



Here is a chart of cloud cover in the tropics and SST.

http://farm9.staticflickr.com/8502/8414560775_8224e28317_b_d.jpg



Here is a chart of global temp vs cloud cover (scatter plot).

http://farm9.staticflickr.com/8223/8415656464_9ab09b7236_b_d.jpg



Apologies for not posting the data, but the data source server has been down for a few days. The charts are here: http://www.climate4you.com/ClimateAndClouds.htm#Tropical%20cloud%20cover%20and%20global%20air%20temperature

Answer 2

Your statement is pretty much correct, but it's hard to get a definitive answer as there are many feedbacks to an increase in the Earth's temperature. GN Plass calculated that doubling the amount of CO2 in the atmosphere, with everything else held constant, would itself cause a 3 to 4°C rise in the Earth's temperature. When you add in the feedback loops, chances are that the temperature of the earth would be considerably higher although as some people pointed out there are a few negatives in the feedback.



You're also right about equilibrium, as it will take the Earth a long time to reach equilibrium, but the release of CO2 from the oceans and the tundra will just shift the time it takes to reach equilibrium further into the future. There is a method in science called perturbation theory that examines how the secondary effects change the primary effect.



And there are other factors at work. Since about 1960, solar insolation has decreased slightly. According to Milankovitch cycles we should be in a long slow cooling period for the next 20,000 years, so those two will mitigate some of the warming as would any major volcanic eruption.

Answer 3

"@Trevor: " increasing phases of CO2 and different GHG’s has to influence in a higher retention of heat, this is ruled by the legal guidelines of thermodynamics and quantum mechanics, adore it or no longer there’s no escaping it." This declaration is correct in isolation with CO2 the one variable changing like in lab conditions. Nevertheless, within the climate approach there are feedbacks (both positive and negative) when you consider that there are various variables and processes interacting. In nature there are plenty of examples the place the confident addition of a variable results in terrible feedbacks being extra powerful. I'm no longer pronouncing that is the case with CO2 within the surroundings i'm just saying it's no longer inconceivable and it would now not spoil any legal guidelines of physics." Charitably, your "rebuttal" to Trevor is fallacious. You can't have a feedback of any form overpowering a nonexistent outcome. Some feedback might be in all probability overpower elevated heat retention from CO2, however that doesn't negate the fact that CO2 increase must increase warmth retention. You appear to be doing all your best to muddy up scientific pondering. If ample humans point out that your reasoning is flawed, we could get expanded scientific understanding - but it doesn't erase your customary strive, just the unwanted side effects.

Answer 4

I would guess that this best estimate does not account for the cyclical nature of CO2 release. In other words, I suspect that your statement in #2 is the correct one, that the estimates do not consider out-gassing from warmer oceans, only for the direct CO2 release.



If you really need to know I would recommend going back to the source of these estimates and looking at the methodology.

Answer 5

A doubling of carbon dioxide, for the purpose of calculating climate sensitivity includes the carbon dioxide that would be added by the feedback. However, when carbon dioxide reaches 540ppm or 790ppm, out gassing and oxidation of methane will add additional carbon dioxide to the atmosphere.

Answer 6

Have you got a link for the "outgassing?' I wonder how large a factor it might be to begin with.

Answer 7

The feedback values are a totally unknown factor at the moment. No one can even state whether they will be positive or negative at this stage, much less put a value on them.