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Comment by chasil | Hacker News Reader

We know that we are living in an icehouse phase, and earth will return to a greenhouse in time, irrelevant to us.

"Earth has been in a greenhouse state for about 85% of its history... Earth is now in an icehouse state, and ice sheets are present in both poles simultaneously."

https://en.m.wikipedia.org/wiki/Greenhouse_and_icehouse_Eart...

This change would be extremely traumatic for humans, as our whole species existence has been in an icehouse.

The good news is that we have only raised co2 levels by one hundred parts per million (to 450) in the whole history of industrial output.

Our impact is not as great as we think, as the cretaceous saw co2 at 5,000-15,000ppm.

If we want to hold the earth under 500ppm, I think, with our ingenuity and growing knowledge, that this can be done.

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Yeah, the earth has been cooling down and heating up throughout the history.

Yet, the spike in Co2 levels just after the industrial revolution is unlike any spike earth has ever had naturally. The Earth has never had this drastic changes to its climate as it had in this span of time. Earth's climate has always been changing, but the change was gradual. 200 years is just a blink of an eye in the context of a planet - changes as drastic as we observe today, have never taken place naturally before.

This cannot be true, considering the superplumes of the cretaceous.

You are correct; the Earth has experienced CO2 rise of this speed before (as far as we know). But not for millions of years, and each time would have been a mass extinction event. https://earth.org/data_visualization/a-brief-history-of-co2/

Just because it's happened before (millions of years ago) doesn't mean it's not serious.

Previously the Earth was struck by a giant asteroid, causing a mass extinction event that more or less leads directly to the rise of mammals. Therefore, it's no big deal for us if that happens again.

These things are going to happen.

Perhaps, for a time, we can intervene. Perhaps not.

Yep so let’s not even try even if tons of experts worldwide say it’s doable.

> the cretaceous saw co2 at 5,000-15,000ppm

Is this correct? The data I can see shows more like 1,000-2,000ppm.

I can only point to this interview, which I read some years ago. Fascinating, in its entirety.

"In any event, large dinosaurs really required to be living in an oxygen tent. An atmosphere in the neighborhood of 35 percent oxygen would be considerably more compatible with large dinosaurs than one in the neighborhood of 28...

"When the super plumes come and carbon dioxide increases, and the oxygen correspondingly increases as a result of photosynthesis.

"The Cretaceous is clearly a green house period as opposed to the present ice house that we have. The Cretaceous is a time of tremendous biological diversity. It is usually said among ecologists today that it is not possible to have more than seven trophic levels in a trophic pyramid. I would be willing to bet, looking at how I have seen ecosystems in the Cretaceous, that there were at least eight and maybe nine trophic levels possible, which would require very much higher temperatures and a much richer food supply than is available at the moment. Well, the rich carbon dioxide of course provides for a much greater biogenic diversity.

"One of the problems that people have always suggested about these high levels of oxygen at various times in the past, is that this is comparable to what you have in an oxygen tent in a hospital. And what about wildfires? What they forget is that the reason for this high oxygen is that there is also a high carbon dioxide level. We are talking about carbon dioxide levels 6 to 10 times the present carbon dioxide level. And that is more than enough to essentially combat wildfires."

https://profjoecain.net/wp-content/uploads/2018/06/robert-e-...

Those estimates seem to be outdated.

https://www.nature.com/articles/s41598-017-08234-0

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