4 ms·

The dispersion assumption tends to make the estimate more rather than less conservative.

by pvg 1y ago

horsawlarway 1y ago
I think the contention is that I don't have an intuition for how molecules actually disperse, but I do know that general climate trends certainly aren't "random dispersion". Ex - we see consistent, long term, patterns in weather that make it unlikely that this dispersion is anything close to "ideal gas in a chamber" style dispersion. Further - we have all sorts of compounding effects. Ex - atmospheric escape is a real thing, plants do nitrogen fixation, hydrogen and oxygen can be bound up in the oceans, etc... Maybe 2000 years is enough time for real random dispersion, maybe it's not. But it's a huge assumption baked into this that doesn't feel especially reasonable to me. All we have is this: >If we assume that a breath diffuses evenly throughout the atmosphere and that these molecules are preserved over time (a reasonable assumption—nitrogen is relatively inert) Which... I challenge is likely not a particularly reasonable assumption to base this on.
- kortilla 1y ago
  Long term climate patterns are much slower than dispersion.
- pvg 1y ago
  we have all sorts of compounding effects. It's still an atmosphere mostly made of nitrogen, on a scale vastly exceeding 2000 years. I don't have an intuition for how molecules actually disperse, but I do know that general climate trends certainly aren't "random dispersion". Big volcano eruptions make for pretty sunsets across the world. Nuclear testing fallout is detectable in everything since atmospheric nuclear testing began. Everywhere we find the K-P boundary, we find iridium. The counter-assumption (which may well be true!) is the counter-intuitive one.
- hnuser123456 1y ago
  The jetstream moves north and south over the US in somewhat predictable ways each year. But the molecules in the jetstream never stop flowing, and the jetstream tends to diverge after it reaches the Atlantic ocean. Sometimes it does another tight lap around the artic circle, sometimes it veers down towards Africa, sometimes it splits and goes both ways: https://en.wikipedia.org/wiki/File:Aerial_Superhighway.ogv https://en.wikipedia.org/wiki/File:Aerial_Superhighway.ogv The jetstream blows at around 110 mph, and Earth's circumference at mid-northern latitudes is around 12500 miles, so it takes 12500/110=114 hours or just under 5 days for the jets to complete a lap around the planet, assuming we choose a molecule that doesn't take a diverging path on that lap. That's 73 laps per year, so 2000 years is nearly 150,000 times that the faster parts of the atmosphere have circled the globe, twisting, breaking, and reconnecting paths the whole time.
advisedwang 1y ago
It depends where you are. If you live in Italy, assuming dispersion makes the estimate more conservative (ie the assumption that it has dispersed means there is less of caesar's breath near you than the alternative) but if you live in Australia, it is less conservative (ie dispersion favours there being caesar breath near you).

The dispersion assumption tends to make the estimate more rather than less conservative.

by pvg 1y ago

The dispersion assumption tends to make the estimate more rather than less conservative.

I think the contention is that I don't have an intuition for how molecules actually disperse, but I do know that general climate trends certainly aren't "random dispersion". Ex - we see consistent, long term, patterns in weather that make it unlikely that this dispersion is anything close to "ideal gas in a chamber" style dispersion. Further - we have all sorts of compounding effects. Ex - atmospheric escape is a real thing, plants do nitrogen fixation, hydrogen and oxygen can be bound up in the oceans, etc... Maybe 2000 years is enough time for real random dispersion, maybe it's not. But it's a huge assumption baked into this that doesn't feel especially reasonable to me. All we have is this: >If we assume that a breath diffuses evenly throughout the atmosphere and that these molecules are preserved over time (a reasonable assumption—nitrogen is relatively inert) Which... I challenge is likely not a particularly reasonable assumption to base this on.

kortilla 1y ago
Long term climate patterns are much slower than dispersion.
pvg 1y ago
we have all sorts of compounding effects. It's still an atmosphere mostly made of nitrogen, on a scale vastly exceeding 2000 years. I don't have an intuition for how molecules actually disperse, but I do know that general climate trends certainly aren't "random dispersion". Big volcano eruptions make for pretty sunsets across the world. Nuclear testing fallout is detectable in everything since atmospheric nuclear testing began. Everywhere we find the K-P boundary, we find iridium. The counter-assumption (which may well be true!) is the counter-intuitive one.
hnuser123456 1y ago
The jetstream moves north and south over the US in somewhat predictable ways each year. But the molecules in the jetstream never stop flowing, and the jetstream tends to diverge after it reaches the Atlantic ocean. Sometimes it does another tight lap around the artic circle, sometimes it veers down towards Africa, sometimes it splits and goes both ways: https://en.wikipedia.org/wiki/File:Aerial_Superhighway.ogv https://en.wikipedia.org/wiki/File:Aerial_Superhighway.ogv The jetstream blows at around 110 mph, and Earth's circumference at mid-northern latitudes is around 12500 miles, so it takes 12500/110=114 hours or just under 5 days for the jets to complete a lap around the planet, assuming we choose a molecule that doesn't take a diverging path on that lap. That's 73 laps per year, so 2000 years is nearly 150,000 times that the faster parts of the atmosphere have circled the globe, twisting, breaking, and reconnecting paths the whole time.

advisedwang 1y ago

It depends where you are. If you live in Italy, assuming dispersion makes the estimate more conservative (ie the assumption that it has dispersed means there is less of caesar's breath near you than the alternative) but if you live in Australia, it is less conservative (ie dispersion favours there being caesar breath near you).