Honest Question About Anthropomorphic Global Warming

[Carrikature]

So why is our 3% not being reabsorbed or lost into space like the 97% of natural CO2?

Because the system is slow and more or less balanced. It would eventually become reabsorbed, but you're talking over the course of millennia.

[Leonhard]

So why is our 3% not being reabsorbed or lost into space like the 97% of natural CO2?

There's not much of a loss to space. And some of our CO2 is being reabsorbed, mostly by the ocean, which is absorbing something like 40% of it, but not all of it. And the rest, if its absorbed by the biosphere, wouldn't decrease CO2 in the atmosphere, it would still increase it, as plant matter dies, the carbon would escape again, causing a net increase in the CO2.

[seer]

There's not much of a loss to space. And some of our CO2 is being reabsorbed, mostly by the ocean, which is absorbing something like 40% of it, but not all of it. And the rest, if its absorbed by the biosphere, wouldn't decrease CO2 in the atmosphere, it would still increase it, as plant matter dies, the carbon would escape again, causing a net increase in the CO2.

But natural CO2 was much higher in that past - correct - when most of the earth was pretty much tropical?

[Leonhard]

But natural CO2 was much higher in that past - correct - when most of the earth was pretty much tropical?

Yes but you have to understand the Earth started out with extremely large amounts of CO2 in the atmosphere, which was then absorbed by the biosphere and sequestered under the ocean floor. So the history of the CO2 in the atmosphere is overall a picture of it dropping down from extreme levels 500 million years ago.

[Carrikature]

I'd recommend checking out this site on The Carbon Cycle. I think it will clear up most of your questions along this line. It's not technical at all outside of some quantities.

[TheLurch]

But natural CO2 was much higher in that past - correct - when most of the earth was pretty much tropical?

Yep, things like volcanic activity, the rate of weathering, and the positions of the continents can all influence the carbon cycle by changing the amount of carbon stored in the deep oceans or in rocks and sediments. So the earth has experienced different levels of atmospheric carbon in the past, and correspondingly different temperatures. These range from the snowball earth phases to hothouses where crocodilians could inhabit the poles.

[seer]

Yes but you have to understand the Earth started out with extremely large amounts of CO2 in the atmosphere, which was then absorbed by the biosphere and sequestered under the ocean floor. So the history of the CO2 in the atmosphere is overall a picture of it dropping down from extreme levels 500 million years ago.

Well yes it dropped down, then we had the ice age, then it went up again to present. And I'm not sure what you mean by extreme - life seemed to have flourished quite well with a warmed climate.

[Leonhard]

Well yes it dropped down, then we had the ice age, then it went up again to present. And I'm not sure what you mean by extreme - life seemed to have flourished quite well with a warmed climate.

I have to be honest I'm not an expert on the ice age cycles as they're called, what drives them. They take place over time frames of dozen of millenia is about all I know.

[Leonhard]

It should also be said that we were at one of the peaks in the cycle around the seventies. The natural cycle would have taken the CO2 concentration downwards, not upwards again. We're the reasons its continuing to go upwards, which might save us from a global cooling scenario a few millenia down the road.

However when you said 'much larger in the past' I was thinking about the carbon of a few hundred million years ago.

[Carrikature]

Well yes it dropped down, then we had the ice age, then it went up again to present. And I'm not sure what you mean by extreme - life seemed to have flourished quite well with a warmed climate.

The issue there is mostly rate of change. When you're changing temperature over the course of thousands of years, species have time to adapt accordingly. Some can't and go extinct, and others may change quite a bit, but the chance still exists. Changing temperature over the course of ~200 years doesn't give nearly enough time for that.

In fact, I would say one of the most inadvertent things humans are doing to the ecosystem is selecting for high rates of evolution and/or adaptability. That means that short generation cycles (like with bacteria, rodents, and insects) can keep pace while longer cycles (like elephants and big cats) can't.

[TheLurch]

I have to be honest I'm not an expert on the ice age cycles as they're called, what drives them. They take place over time frames of dozen of millenia is about all I know.

They're driven by subtle changes in the earth's orbit and axis of rotation. Good information on them here:
https://en.wikipedia.org/wiki/Milankovitch_cycles

On their own, the orbital changes would have a very weak effect, but they're reinforced by changes in CO2. The best hypothesis for how that i've seen involves ice expanding from Antarctica. The orbital changes are enough to trigger that sort of expansion, which covers an area where deep ocean waters normally upwell to the surface, releasing CO2 into the atmosphere. Once that's covered in ice, the CO2 exchange doesn't take place, and the carbon remains trapped in the deep ocean. Melting the ice reverses this process. Lots of evidence indicating that there is excess carbon in the deep Southern Ocean during the last glacial period.

[37818]

The three main atmospheric gases are Nitrogen, N₂ at 78%, Oxigen, O₂ at 21% and Argon, Ar at 1%. Now CO₂ is only about.04%, that's about 400 parts per mlllion. Over the last 50 some years only a CO₂ incress of about 100 part per million.

where-does-co2-come-from_3.jpg

[TheLurch]

Could i ask where that graph came from? Because those numbers don't look right, and i'd like to understand how they're derived.

[Leonhard]

I second TheLurch's opinion, that pie chart looks kinda bogus. In general if something is a piechart its already kinda suspect, as its not really something that's used in science at all.

Its true that the quantity of Oxygen and Nitrogen is far greater than CO2, but that is not that important, because Nitrogen is a very weak absorber of infrared radiation, so it has negligible effect. Oxygen absorb a little bit. However the effect is dominated by CO2 and especially H2O, both of which overwhelm the absorption spectrum of solar radiation.

The second thing to know is that the effect of an increase in density is not proportional but rather logarithmic, so doubling the amount of a gas in the atmosphere, only increases how much is absorbed by a small increment. Methane in principle is a lot worse than CO2, but the quantity of methane in the atmosphere is entirely negligible.

Take a look at this absorption spectrum and you can see what parts are dominated by what gas.

[shunyadragon]

The three main atmospheric gases are Nitrogen, N₂ at 78%, Oxigen, O₂ at 21% and Argon, Ar at 1%. Now CO₂ is only about.04%, that's about 400 parts per mlllion. Over the last 50 some years only a CO₂ incress of about 100 part per million.

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It's the gas distribution in apple pie.