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Comment by changoplatanero | Hacker News Reader

Imagine if the entire developed world suddenly magically disappeared so that no further emissions happened from that population. Would the existing co2 in the atmostphere still be enough to cause 2 degrees of warming?

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Yes, even if we completely eliminate carbon emissions, our current carbon debt is around 1 trillion tons [1]. We'll need to remove that much carbon from the atmosphere within 50 years or so, given we stop all of our emissions today.

[1]: https://www.youtube.com/watch?v=QyQvfaW54NU

It's quite interesting because if we stoped all emissions right now the temperature would increase due to lack of aerosol emissions. It's speculated that air quality regulations in Europe led to warming of arctic by 0.5°C (https://www.nature.com/articles/ngeo2673).

Most likely yes - there are a bunch of feedback loops in climate that continue even if the initial source of warming is removed.

The most likely scenario that would result in the "entire developed world suddenly magically disappeared" is a nuclear winter, though. Such an event would drop global temperatures by a lot more than 2 C, nullifying the problem.

that's why i said "magically disappeared" instead of "blew itself up with nuclear weapons" :)

But for how long, and does that remove the carbon or just mask the problem while the carbon remains?

> The most likely scenario that would result in the "entire developed world suddenly magically disappeared" is a nuclear winter

Please don't give politicians ideas.

Everyone thought that "The Wall" was a joke, and yet...

The half life of CO2 in the atmosphere is about 30 years (2.5%/yr). We're currently at ~400ppm, whereas before industrialization we were at ~250 (there are other sources). So yes, if we stopped anthropogenic CO2 we would very likely avoid a 1.5C increase.

"half life of CO2 in the atmosphere" is a bit misleading, (most|some) people will think it means the quantity of CO2 in the atmosphere halves every 30 years. That is false.

This NASA link says CO2 stays in the atmosphere for hundreds of years: https://climate.nasa.gov/news/2915/the-atmosphere-getting-a-...

And this site: https://www.skepticalscience.com/co2-residence-time.htm

explains that while the individual molecule CO2 hangs around the atmosphere for 3-4 years, it's then merely exchanged with one in the oceans (or maybe one in a rotting tree).

On this study: https://scholars.unh.edu/cgi/viewcontent.cgi?referer=https:/...

on page 4 (shown 25 on the page), you can see the box model of the global carbon cycle. Halflife refers on how long the a CO2 molecule spends in a given box.

There are other second-order effects that continue, eg. reduced albedo as the polar ice melts, methane emissions as the permafrost thaws, increased weathering of carbonates.

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