[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%

[mikeash]

Your 4% number is also based on emission rates. My number and yours are both nonsense for the same reason. You can't make the attribution by looking at emissions alone.