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I've been trying like the dickens to get a solid understanding of the numbers behind this, but they all seem to vary so much depending on source. A recent clim

I've been trying like the dickens to get a solid understanding of the numbers behind this, but they all seem to vary so much depending on source. A recent climate report indicated that as of 2011, the earth's atmosphere has somewhere around 1900 gigatons of CO2 and that we'd need to stay below 2900 gigatons to stay below 2 degrees celsius of warming. But other sources report carbon in terms of ppm, and this source says the world is at 407.4 ppm. One source I found says that 1 ppm = 7.81 gigatons of CO2, but that would mean we're at 3181.8 gigatons of CO2 worldwide, which is much higher than any other estimate I've seen - another estimate I saw said that the world is slated to go above 2900 gigatons in the year 2036 if current emission rates hold steady, but this one says we're already far over that. Is there a source somewhere that tracks the latest state of the basic math? Math that there is some general consensus on, based off of emissions of CO2 per country per year, emissions of CO2 of the world per year, ppm, gigatons, and the generally-agreed-upon correlation between that and degrees of warming? Because all these reports seem to disagree with each other. (What's nice about having an upper limit like 2900, and a rate of emissions per country, is that you can then calculate how much carbon each citizen needs to offset and/or sequester.)

deleted 7y ago
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skybrian 7y ago
I don't know much about it, but I believe ppm is what instruments measure, and how that translates to temperature rise is going to depend on the climate model? You might have better luck looking for what climate models predict. It's not going to be basic math since climate is complicated. Maybe there is a toy model based on linear effects, but that's going to be a crude summary at best.
- tunesmith 7y ago
  I'm fine with there just being a recognized source with wide consensus that says "we have to stay below x ppm/GTCO2 to stay below 2 degrees, and y to stay below 1.5, and currently we are at z." And, data on emissions rate, but those appear to be more consistent. From that you can calculate how much time we have. But so far it appears that our "scientific consensus" on those numbers range between "we have fifty years" to "we're already past that point".
  - skybrian 7y ago
    The closest thing I've seen are graphs predicting temperature rise under different scenarios.
  - supercow12 7y ago
    There are predictions based on various scenarios. you can see them in more detail here: https://science2017.globalchange.gov/chapter/4/ https://science2017.globalchange.gov/chapter/4/ And the various probabilities that we will stay below X degrees under the various scenarios can be found in figure 14.3 here: https://science2017.globalchange.gov/chapter/14/ https://science2017.globalchange.gov/chapter/14/ I think you are seeing an artifact of how difficult it is to explain things to non-scientists (and non-scientists misinterpreting the claims). It also tends to be difficult to find these kinds of good sources with a generic google search and no prior knowledge of the appropriate search terms. Using google scholar instead can be helpful sometimes in weeding out non-science answers for science questions.
    - tunesmith 7y ago
      It's too bad, because I think people need to be able to make at least a simple version of the argument for themselves, from premises, rather than simply relying on "Scientists say..." Edit: Another example. The source you listed says the world is emitting just under 10 GtC/year. Another source I've recently seen said we are emitting 37.1 GtC/year. I've also heard 54/year but don't remember where. I mean, these numbers aren't even close.
      - skybrian 7y ago
        Hmm, I didn't see where it says 10 GtC/year, but perhaps I missed it. Could you be more specific? Looking at Figure 2.7 [1] they have "Fossil fuels and industry" at what looks like about 37, which agrees with your other source? The discrepancy in numbers might just be from measuring different things. [1] https://science2017.globalchange.gov/chapter/2/ https://science2017.globalchange.gov/chapter/2/
        7y ago
phaemon 7y ago
The 1 ppm = 7.81Gt is correct, but the 2900Gt figure isn't atmospheric total, it's total emissions. Not all emissions end up staying in the atmosphere, so it doesn't translate exactly across.
- tunesmith 7y ago
  Thanks - I didn't realize that this is actually one of arguments that skeptics make - the matter of the correlation between CO2 in the atmosphere, and CO2 emissions. I see some indications that the rule of thumb is that roughly 60% of emissions stay in the atmosphere, which makes the current numbers make more sense again, but so far I haven't found anything more authoritative. And I see some estimates that 430 ppm corresponds to 1.5 degrees, while 450 ppm corresponds to 2 degrees, but 60% doesn't work for the 2900gT = 2 degrees estimate.

deleted 7y ago

[deleted]

skybrian 7y ago

I don't know much about it, but I believe ppm is what instruments measure, and how that translates to temperature rise is going to depend on the climate model? You might have better luck looking for what climate models predict. It's not going to be basic math since climate is complicated. Maybe there is a toy model based on linear effects, but that's going to be a crude summary at best.

tunesmith 7y ago
I'm fine with there just being a recognized source with wide consensus that says "we have to stay below x ppm/GTCO2 to stay below 2 degrees, and y to stay below 1.5, and currently we are at z." And, data on emissions rate, but those appear to be more consistent. From that you can calculate how much time we have. But so far it appears that our "scientific consensus" on those numbers range between "we have fifty years" to "we're already past that point".
- skybrian 7y ago
  The closest thing I've seen are graphs predicting temperature rise under different scenarios.
- supercow12 7y ago
  There are predictions based on various scenarios. you can see them in more detail here: https://science2017.globalchange.gov/chapter/4/ https://science2017.globalchange.gov/chapter/4/ And the various probabilities that we will stay below X degrees under the various scenarios can be found in figure 14.3 here: https://science2017.globalchange.gov/chapter/14/ https://science2017.globalchange.gov/chapter/14/ I think you are seeing an artifact of how difficult it is to explain things to non-scientists (and non-scientists misinterpreting the claims). It also tends to be difficult to find these kinds of good sources with a generic google search and no prior knowledge of the appropriate search terms. Using google scholar instead can be helpful sometimes in weeding out non-science answers for science questions.
  - tunesmith 7y ago
    It's too bad, because I think people need to be able to make at least a simple version of the argument for themselves, from premises, rather than simply relying on "Scientists say..." Edit: Another example. The source you listed says the world is emitting just under 10 GtC/year. Another source I've recently seen said we are emitting 37.1 GtC/year. I've also heard 54/year but don't remember where. I mean, these numbers aren't even close.
    - skybrian 7y ago
      Hmm, I didn't see where it says 10 GtC/year, but perhaps I missed it. Could you be more specific? Looking at Figure 2.7 [1] they have "Fossil fuels and industry" at what looks like about 37, which agrees with your other source? The discrepancy in numbers might just be from measuring different things. [1] https://science2017.globalchange.gov/chapter/2/ https://science2017.globalchange.gov/chapter/2/
      - 7y ago

phaemon 7y ago

The 1 ppm = 7.81Gt is correct, but the 2900Gt figure isn't atmospheric total, it's total emissions. Not all emissions end up staying in the atmosphere, so it doesn't translate exactly across.

tunesmith 7y ago
Thanks - I didn't realize that this is actually one of arguments that skeptics make - the matter of the correlation between CO2 in the atmosphere, and CO2 emissions. I see some indications that the rule of thumb is that roughly 60% of emissions stay in the atmosphere, which makes the current numbers make more sense again, but so far I haven't found anything more authoritative. And I see some estimates that 430 ppm corresponds to 1.5 degrees, while 450 ppm corresponds to 2 degrees, but 60% doesn't work for the 2900gT = 2 degrees estimate.