[ChemicalWarfare]

That's not what I asked. If total CO2 in the atmosphere is 100%, what portion of that number is attributed to human activity? Also, CO2 itself - out of all of the greenhouse gases in the atmosphere - what percentage belongs to CO2?

[mikeash]

How is that not what you asked? If we've increased the amount by 50% over preindustrial levels, then the current portion attributable to us is about 33%.

[ChemicalWarfare]

...except that figure is less than 4%. about 8 gigatons are attributed to humans out of ~220 gigatons injected into the atmosphere overall on a yearly basis.

the kicker is - the percentage of CO2 in the overall greenhouse pool is also in the single digits, the most significant (volume-wise) greenhouse gas which comprises about 95% of the greenhouse gases in the atmosphere is water vapor.

so if you factor that in - if humanity ceases to exist tomorrow, there is a potential for a .3% change in greenhouse gas volumes.

[Brakenshire]

> ...except that figure is less than 4%. about 8 gigatons are attributed to humans out of ~220 gigatons injected into the atmosphere overall on a yearly basis.

This is like the difference between profit and savings. Accumulated CO2 is a savings accounts, and the pre-industrial climate in the short term acts like a business which has zero profit, balanced revenues and expenditure. If you come into the business, and hold expenditure the same, but increase revenues by 4%, and yield a 4% profit, which every year you put in the bank account, that is going to accumulate over time. And the warming is created by the accumulation. You talk about a 4% yearly excess as if that was a small amount!

Also, your point about water vapour ties into what I said in the earlier comment, a lot of the warming is exactly that secondary effect - CO2 has a direct heating effect, that raises temperature, which then raises the partial pressure of water vapour, which increases concentrations of water vapour in the atmosphere, which as you say is a very important greenhouse gas. It's the combination of these two effects, of direct CO2 warming, causing increased water vapour concentration, which accounts for the baseline warming which everyone who is sceptical of computer models should believe in. This very well-established baseline warming accounts for about half of the climate sensitivity proposed by the IPCC, if you think computer models are junk, that discounts many of the positive feedbacks proposed, but also the negative feedbacks which would have to exist, to lead to zero warming.

[ChemicalWarfare]

>> You talk about a 4% yearly excess as if that was a small amount!

This analogy would only make sense if somehow this 4% wasn't spent or was spent differently than the rest of the money. Also don't forget we're talking .3% if you take all of the greenhouse gases into consideration.

>>...if you think computer models are junk, that discounts many of the positive feedbacks proposed, but also the negative feedbacks which would have to exist, to lead to zero warming.

This sounds like mental gymnastics trying to single out the evuuhl CO2. Given the fact that planet Earth went through multiple heating/cooling cycles way more severe than the current warming trend without any antropogenic influence, applying Occam's razor here would lead me to believe the issue lies elsewhere.

[mikeash]

If you want to just examine emissions, humans have emitted about 1.5 trillion tonnes of CO2 since the industrial revolution, and the atmosphere contains about 3.2 trillion tonnes of CO2 in total. So if you go by that reasoning, we're responsible for about 47% of the total.

[ChemicalWarfare]

that's not apples to apples. how much CO2 was naturally emitted in that timeframe? that would be an apples-to-apples comparison.

[mikeash]

So you understand that the amount emitted over time is not equal to the amount currently present? Why, then, do you compare emissions when your question was about the amounts currently present?

[ChemicalWarfare]

>> So you understand that the amount emitted over time is not equal to the amount currently present?

I do, but you don't seem to since you came back with an attempt to quantify the "amount emitted over time"

my question was: >>> what percentage of CO2 in the atmosphere is attributed to human activity?

...and I even answered it myself :) ... it's ~4%