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Water vapor (clouds) also reflects sunlight. So it's complicated. We know the planet has had higher CO2 and higher temperatures in the past, and it did not "run

Water vapor (clouds) also reflects sunlight. So it's complicated. We know the planet has had higher CO2 and higher temperatures in the past, and it did not "run away"

viraptor 9mo ago
It doesn't matter if the top of the curve flattens out, if we can't survive outside of the bottom part that looks exponential.
teamonkey 9mo ago
It might not run away to infinity, but it may well run away in the sense that the rate of change could continue to increase even if humans stop contributing to it.
panarchy 9mo ago
We can't say for sure that the current feedback loops will be identical to those that did or did not exist in the past. Differences in the initial state could result in different outcomes. For example was there as much methane trapped in the arctics during the last time CO2 was high? Does the rate of the increase of CO2 and temperature have an effect? Because it's currently getting hotter far faster (absurdly so) than any other period we have records for.
fc417fc802 9mo ago
No citations to hand but Antarctica used to be temperate rainforest and many of the conditions of present day tropical rainforests and savanna could be found much farther from the equator. The paleocene–eocene thermal maximum makes for interesting related reading. https://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_thermal_maximum https://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_therm...
Windchaser 9mo ago
> Water vapor (clouds) also reflects sunlight. So it's complicated. We know the planet has had higher CO2 and higher temperatures in the past, and it did not "run away" Yes. But stars like ours burn brighter as they move through their lifetimes, and the Sun is a bit brighter now than it was back when we had higher CO2 levels. That's why a runaway GHG didn't happen back then, but is basically guaranteed to happen within a billion years.
- SV_BubbleTime 9mo ago
  So… the sun is hotter now than it was what… since the 1950s? The 1850s? The Jurassic period? What scale is do you need to make this claim reasonable? Also, I see a lot of things presented as facts in your comment, you seem to have convinced yourself quite thoroughly.
  - jemmyw 9mo ago
    10% every billion years. So negligible on our timescale, but it is significant if you talk about ancient climate conditions like this thread does.
    - blueflow 9mo ago
      complex life on earth is half a billion years old (cambrian explosion 550ma ago), so the sun shouldn't be that much of an factor.

Water vapor (clouds) also reflects sunlight. So it's complicated. We know the planet has had higher CO2 and higher temperatures in the past, and it did not "run away"

viraptor 9mo ago

It doesn't matter if the top of the curve flattens out, if we can't survive outside of the bottom part that looks exponential.

teamonkey 9mo ago

It might not run away to infinity, but it may well run away in the sense that the rate of change could continue to increase even if humans stop contributing to it.

panarchy 9mo ago

We can't say for sure that the current feedback loops will be identical to those that did or did not exist in the past. Differences in the initial state could result in different outcomes. For example was there as much methane trapped in the arctics during the last time CO2 was high? Does the rate of the increase of CO2 and temperature have an effect? Because it's currently getting hotter far faster (absurdly so) than any other period we have records for.

fc417fc802 9mo ago

No citations to hand but Antarctica used to be temperate rainforest and many of the conditions of present day tropical rainforests and savanna could be found much farther from the equator. The paleocene–eocene thermal maximum makes for interesting related reading. https://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_thermal_maximum https://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_therm...

Windchaser 9mo ago

> Water vapor (clouds) also reflects sunlight. So it's complicated. We know the planet has had higher CO2 and higher temperatures in the past, and it did not "run away" Yes. But stars like ours burn brighter as they move through their lifetimes, and the Sun is a bit brighter now than it was back when we had higher CO2 levels. That's why a runaway GHG didn't happen back then, but is basically guaranteed to happen within a billion years.

SV_BubbleTime 9mo ago
So… the sun is hotter now than it was what… since the 1950s? The 1850s? The Jurassic period? What scale is do you need to make this claim reasonable? Also, I see a lot of things presented as facts in your comment, you seem to have convinced yourself quite thoroughly.
- jemmyw 9mo ago
  10% every billion years. So negligible on our timescale, but it is significant if you talk about ancient climate conditions like this thread does.
  - blueflow 9mo ago
    complex life on earth is half a billion years old (cambrian explosion 550ma ago), so the sun shouldn't be that much of an factor.