Comment by marcosdumay

To put it further into numbers -

1). Wikipedia does have a citation [1] saying 2,450 gigatonnes of CO2 have been emitted by human activity, of which 42% stayed in the atmosphere and 34% dissolved in the oceans, with the rest already sequestered by plant growth and land use. As we start to pull CO2 out of the atmosphere, it will begin to be emitted from the oceans as well; therefore, let's assume we have to recapture all excess atmospheric and oceanic CO2:

:: 2450x10^9 tonnes CO2 x .66 fraction to sequester ~= 1.6x10^12 tonnes CO2.

2) Let's convert the CO2 to something more stable for long-term storage: HDPE.

- Convert mass of CO2 to mass of carbon:

:: 1.6x10^12 tonnes CO2 x 12/44 mass fraction of C in CO2 ~= 4.4x10^11 tonnes C

- Convert mass C to mass HDPE; assume HDPE is effectively (CH2)n. Then:

:: 4.4x10^11 tonnes C x 14/12 mass fraction CH2 to C ~= 5.2x10^11 tonnes HDPE

3) That's a lot of plastic! How much volume? Wikipedia says HDPE is ~930-970 kg/m3; let's be conservative again and take the low figure:

:: 5.2x10^11 tonnes HDPE x 1.0/0.930 m3 per tonne HDPE ~= 5.5x10^11 m3 HDPE

4) Those are cubic meters; how about cubic kilometers?

:: 5.5x10^11 m3 x 1.0/1.0x10^9 km3 per m3 ~= 5.5x10^2 km3

In other words, if you turned all the [excess potentially climate-change impacting] CO2 that humanity has emitted since 1850 into plastic (a process that would certainly emit a large additional CO2 fraction given the industrial buildout required) then we'd end up with about 550 cubic kilometers of the stuff. Coincidentally, that's about the volume of Mount Everest according to an intermediate calculation in [2].

So, a mountain of carbon: more than a pile but less than a mountain range.

[1] https://en.wikipedia.org/wiki/Carbon_dioxide_in_the_atmosphe...

[2] https://www.quora.com/What-would-the-estimated-weight-of-Mou...

But if you release the O2 and convert it into diamond, then by my highy-suspect back of the envelope calculations, it'd be a diamond that would fit into one square kilometer, 87 meters high. It would make quite the tourist attraction.