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No surprises here. We've known for years we're going to shoot beyond 2C with very high certainty. Even if a miracle happened and we reached zero emissions toda

by pier25 4y ago

No surprises here. We've known for years we're going to shoot beyond 2C with very high certainty. Even if a miracle happened and we reached zero emissions today, the climate will keep warming at least for some more decades due to climate lag and feedbacks.

radford-neal 4y ago
No, this is not known with "very high certainty". The most recent IPCC report (AR6) gives the "very likely" (90% probability) range for "equilibrium climate sensitivity" - the eventual effect on temperature of doubling CO2 - as between 2C and 5C. Current CO2 levels are less than double pre-industrial levels, so the "baked in" warming could well be less than 2C. Also note that reaching the equilibrium temperature takes more like centuries than decades, making the concept somewhat academic, since lots of other things will change over that time period. Also note that 2C warming over pre-industrial temperatures would just take us back to about what the temperature was 8000 years ago, when conditions were good enough for agriculture and civilization to start.
- thebooktocome 4y ago
  Eight thousand years ago we didn’t need the Haber process to keep several billion people fed.
- taylodl 4y ago
  Ah, the ol' earth has been as warm or warmer before claim. This is true - absolutely true, but it misses one critical, I daresay crucial, point: earth's climate has never changed this rapidly in the past few million years. It's the rate of temperature change that's the problem, not necessarily the actual temperature itself since, as you've pointed out, earth has had these temperatures before. Given time, the biosphere will respond positively. If not given sufficient time, as measured in geological time units, the biosphere responds poorly. That fact is the crux of the problem. Also, with regards to your claim that earth was warmer 8,000 ago, that's a bit nuanced. You should check out this article for more details. https://reason.com/2013/03/07/earths-average-temperature-lower-than-it/ https://reason.com/2013/03/07/earths-average-temperature-low...
  - RandomLensman 4y ago
    How sure are we about "never" beyond recent geological history? The impact that finished of the dinosaurs must have brought some pretty rapid changes without killing off the entire biosphere. My understanding is that the stressed parts of the biosphere collapsed pretty quickly within a few generations. But I might be wrong.
- pier25 4y ago
  The last time the Earth was above 400ppm during the Pliocene era, when sea level was roughly 25 meters higher than today. That in itself is going to be catastrophic once the climate and the planet catch up, but there are far worse consequences and emissions are still growing. Have you ever read about the Russian wildfires of 2010 which had a massive impact to global food prices which then triggered the Arab spring revolutions? That was a single event in a world below 400ppm but these heat waves are starting to occur with more frequency now and will have serious consequences. The IPCC is an organization that functions with consensus and their data is awfully outdated. Their assessments generally underreport the consequences of climate change. Here's a paper from 2010 which analyzed this: https://skepticalscience.com/pics/Freudenburg_2010_ASC.pdf https://skepticalscience.com/pics/Freudenburg_2010_ASC.pdf
bayesianbot 4y ago
If we reached actual zero emissions for humans, the ocean absorbing CO2 from air would almost exactly balance the warming climate lag, IIRC. But you're right in a sense that in reality most likely we'd still be emitting CO2, balance it with the natural CO2 sinks and call that net-zero.
- pier25 4y ago
  Maybe but human emissions are only half of the problem. See this comment I wrote about the permafrost: https://news.ycombinator.com/item?id=33362648 https://news.ycombinator.com/item?id=33362648
biotinker 4y ago
Of the amount of CO2 released each year by humans (~30gt), only about half persists in the atmosphere. The other half is re-absorbed by the biosphere. This is based on estimated total biosphere emissions, estimated human emissions, and annual CO2 PPM increases. I did some math on that and wrote it up here if anyone wants to dig deeper: https://biotinker.dev/posts/climate1.html https://biotinker.dev/posts/climate1.html In the case of the zero-emission miracle, atmospheric CO2 levels would start dropping at about the same rate they are currently climbing. As you mention, there is climate lag and feedbacks, but the "return to normal" would start fairly quickly.
- pier25 4y ago
  I'm sorry but I think you're missing a lot in your assumptions. For example, there are only rough estimates on how much methane is trapped in the permafrost. The first estimate I saw by Natalia Shakhova et al was 1400gt over a decade ago (so about 45 years of human emissions at the current rate). I found this recent MIT article which mentions 1500gt [1]. Let's not forget methane has a 25x more heat trapping capacity than CO2. Do the math on that. Also the permafrost is just one of many feedbacks. Another point you're not considering is that the capacity of the biosphere to absorb carbon is being reduced. For example, the Amazon used to be considered a carbon sink but it is becoming a carbon source [2]. [1] https://climate.mit.edu/explainers/permafrost https://climate.mit.edu/explainers/permafrost [2] https://www.nature.com/articles/d41586-021-01871-6 https://www.nature.com/articles/d41586-021-01871-6
  - biotinker 4y ago
    You're right about methane; that's much more difficult to find data on, though, especially with regard to how much would be released and at what point. But if those tipping points get hit, then nothing CO2 related will save us. Feedback loops here dying down I'll classify under the "hope they're included in the miracle that gave us zero carbon emissions" :) I'm not convinced on your second point; I'll need to see more data. I read the paper you linked, it doesn't give hard numbers, so it's difficult to compare the net loss of carbon flux in the amazon, to gain of carbon flux in other areas that are getting net-reforested, such as the eastern United States. Examples of local areas flipping from sink to source, and others becoming larger sinks, don't paint a clear picture of the directionality of the whole system.

by pier25 4y ago

radford-neal 4y ago

No, this is not known with "very high certainty". The most recent IPCC report (AR6) gives the "very likely" (90% probability) range for "equilibrium climate sensitivity" - the eventual effect on temperature of doubling CO2 - as between 2C and 5C. Current CO2 levels are less than double pre-industrial levels, so the "baked in" warming could well be less than 2C. Also note that reaching the equilibrium temperature takes more like centuries than decades, making the concept somewhat academic, since lots of other things will change over that time period. Also note that 2C warming over pre-industrial temperatures would just take us back to about what the temperature was 8000 years ago, when conditions were good enough for agriculture and civilization to start.

thebooktocome 4y ago
Eight thousand years ago we didn’t need the Haber process to keep several billion people fed.
taylodl 4y ago
Ah, the ol' earth has been as warm or warmer before claim. This is true - absolutely true, but it misses one critical, I daresay crucial, point: earth's climate has never changed this rapidly in the past few million years. It's the rate of temperature change that's the problem, not necessarily the actual temperature itself since, as you've pointed out, earth has had these temperatures before. Given time, the biosphere will respond positively. If not given sufficient time, as measured in geological time units, the biosphere responds poorly. That fact is the crux of the problem. Also, with regards to your claim that earth was warmer 8,000 ago, that's a bit nuanced. You should check out this article for more details. https://reason.com/2013/03/07/earths-average-temperature-lower-than-it/ https://reason.com/2013/03/07/earths-average-temperature-low...
- RandomLensman 4y ago
  How sure are we about "never" beyond recent geological history? The impact that finished of the dinosaurs must have brought some pretty rapid changes without killing off the entire biosphere. My understanding is that the stressed parts of the biosphere collapsed pretty quickly within a few generations. But I might be wrong.
pier25 4y ago
The last time the Earth was above 400ppm during the Pliocene era, when sea level was roughly 25 meters higher than today. That in itself is going to be catastrophic once the climate and the planet catch up, but there are far worse consequences and emissions are still growing. Have you ever read about the Russian wildfires of 2010 which had a massive impact to global food prices which then triggered the Arab spring revolutions? That was a single event in a world below 400ppm but these heat waves are starting to occur with more frequency now and will have serious consequences. The IPCC is an organization that functions with consensus and their data is awfully outdated. Their assessments generally underreport the consequences of climate change. Here's a paper from 2010 which analyzed this: https://skepticalscience.com/pics/Freudenburg_2010_ASC.pdf https://skepticalscience.com/pics/Freudenburg_2010_ASC.pdf

bayesianbot 4y ago

If we reached actual zero emissions for humans, the ocean absorbing CO2 from air would almost exactly balance the warming climate lag, IIRC. But you're right in a sense that in reality most likely we'd still be emitting CO2, balance it with the natural CO2 sinks and call that net-zero.

pier25 4y ago
Maybe but human emissions are only half of the problem. See this comment I wrote about the permafrost: https://news.ycombinator.com/item?id=33362648 https://news.ycombinator.com/item?id=33362648

biotinker 4y ago

Of the amount of CO2 released each year by humans (~30gt), only about half persists in the atmosphere. The other half is re-absorbed by the biosphere. This is based on estimated total biosphere emissions, estimated human emissions, and annual CO2 PPM increases. I did some math on that and wrote it up here if anyone wants to dig deeper: https://biotinker.dev/posts/climate1.html https://biotinker.dev/posts/climate1.html In the case of the zero-emission miracle, atmospheric CO2 levels would start dropping at about the same rate they are currently climbing. As you mention, there is climate lag and feedbacks, but the "return to normal" would start fairly quickly.

pier25 4y ago
I'm sorry but I think you're missing a lot in your assumptions. For example, there are only rough estimates on how much methane is trapped in the permafrost. The first estimate I saw by Natalia Shakhova et al was 1400gt over a decade ago (so about 45 years of human emissions at the current rate). I found this recent MIT article which mentions 1500gt [1]. Let's not forget methane has a 25x more heat trapping capacity than CO2. Do the math on that. Also the permafrost is just one of many feedbacks. Another point you're not considering is that the capacity of the biosphere to absorb carbon is being reduced. For example, the Amazon used to be considered a carbon sink but it is becoming a carbon source [2]. [1] https://climate.mit.edu/explainers/permafrost https://climate.mit.edu/explainers/permafrost [2] https://www.nature.com/articles/d41586-021-01871-6 https://www.nature.com/articles/d41586-021-01871-6
- biotinker 4y ago
  You're right about methane; that's much more difficult to find data on, though, especially with regard to how much would be released and at what point. But if those tipping points get hit, then nothing CO2 related will save us. Feedback loops here dying down I'll classify under the "hope they're included in the miracle that gave us zero carbon emissions" :) I'm not convinced on your second point; I'll need to see more data. I read the paper you linked, it doesn't give hard numbers, so it's difficult to compare the net loss of carbon flux in the amazon, to gain of carbon flux in other areas that are getting net-reforested, such as the eastern United States. Examples of local areas flipping from sink to source, and others becoming larger sinks, don't paint a clear picture of the directionality of the whole system.