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The graph shows emissions trajectories projected by the most commonly used climate scenarios (called SSP5-8.5 and RCP8.5, with labels on the right vertical axis

The graph shows emissions trajectories projected by the most commonly used climate scenarios (called SSP5-8.5 and RCP8.5, with labels on the right vertical axis), along with other scenario trajectories. Actual emissions to date (dark purple curve) and those of near-term energy outlooks (labeled as EIA, BP and ExxonMobil) all can be found at the very low end of the scenario range, and far below the most commonly used scenarios. RCP 8.5 was intended as the highest-emissions scenario, not the most likely scenario. "RCP 8.5—A scenario of comparatively high greenhouse gas emissions (2011)" https://link.springer.com/article/10.1007/s10584-011-0149-y https://link.springer.com/article/10.1007/s10584-011-0149-y This paper summarizes the main characteristics of the RCP8.5 scenario. The RCP8.5 combines assumptions about high population and relatively slow income growth with modest rates of technological change and energy intensity improvements, leading in the long term to high energy demand and GHG emissions in absence of climate change policies. Compared to the total set of Representative Concentration Pathways (RCPs), RCP8.5 thus corresponds to the pathway with the highest greenhouse gas emissions. Even 10 years ago, when this paper was published, it was apparent that technology and energy intensity were improving more than the RCP 8.5 scenario posited. I don't know if RCP 8.5 has since been misused as a most common scenario, but the original post quoted above doesn't quantify that either.

incompatible 6y ago
Looking a CO2 measurements, I don't see much sign that the rate of increase is slowing down: https://climate.nasa.gov/vital-signs/carbon-dioxide/ https://climate.nasa.gov/vital-signs/carbon-dioxide/. Do the current models assume it will accelerate even faster?
- pdonis 6y ago
  The article is talking about annual CO2 emissions, not total CO2 levels. CO2 levels and their rate of increase are a lagging indicator; it takes many years for a reduction in emissions to show up in CO2 levels. The models all assume that CO2 emissions will continue to increase; the main difference in the assumptions is how fast emissions are assumed to increase.
sien 6y ago
From the article : "For instance, O’Neill and colleagues find that “many studies” use scenarios that are “unlikely.” In fact, in their literature review such “unlikely” scenarios comprise more than 20% of all scenario applications from 2014 to 2019. They also call for “re-examining the assumptions underlying” the high-end emissions scenarios that are favored in physical climate research, impact studies and economic and policy analyses. As a result of such high prevalence of such studies in the literature, they are also the most commonly cited within scientific assessments of the Intergovernmental Panel on Climate Change. O’Neill and colleagues find that the highest emission scenarios comprise about 30% of all applications in studies over the past five years, from a family of 35 different scenarios that they surveyed."
- adgjlsfhk1 6y ago
  This sounds like good science being done. When you are trying to predict something like carbon emissions, standard practice is to run a few different scenarios. If you run 5 models, one with predicted CO2, and the others with higher and lower values, of course some of your scenarios will be unlikely. You're doing that on purpose so that you have a ability to see how wide the range of possible results is even with uncertainty in CO2.
  - sien 6y ago
    From the article: "Correspondingly, the authors “recommend establishing a process for regular updates” to the scenarios and recommend that key variables in the scenarios “be updated now to be consistent with new historical data.”" So the author is explicitly saying different scenarios should be used, just that they should be updated regularly.
porb121 6y ago
moreover, plenty of scenario work predicts plenty of bad climate effects for rcps and ssps tighter than rcp8.5. by any estimation, the results of rcp8.5 would be disastrous.

incompatible 6y ago

Looking a CO2 measurements, I don't see much sign that the rate of increase is slowing down: https://climate.nasa.gov/vital-signs/carbon-dioxide/ https://climate.nasa.gov/vital-signs/carbon-dioxide/. Do the current models assume it will accelerate even faster?

pdonis 6y ago
The article is talking about annual CO2 emissions, not total CO2 levels. CO2 levels and their rate of increase are a lagging indicator; it takes many years for a reduction in emissions to show up in CO2 levels. The models all assume that CO2 emissions will continue to increase; the main difference in the assumptions is how fast emissions are assumed to increase.

sien 6y ago

From the article : "For instance, O’Neill and colleagues find that “many studies” use scenarios that are “unlikely.” In fact, in their literature review such “unlikely” scenarios comprise more than 20% of all scenario applications from 2014 to 2019. They also call for “re-examining the assumptions underlying” the high-end emissions scenarios that are favored in physical climate research, impact studies and economic and policy analyses. As a result of such high prevalence of such studies in the literature, they are also the most commonly cited within scientific assessments of the Intergovernmental Panel on Climate Change. O’Neill and colleagues find that the highest emission scenarios comprise about 30% of all applications in studies over the past five years, from a family of 35 different scenarios that they surveyed."

adgjlsfhk1 6y ago
This sounds like good science being done. When you are trying to predict something like carbon emissions, standard practice is to run a few different scenarios. If you run 5 models, one with predicted CO2, and the others with higher and lower values, of course some of your scenarios will be unlikely. You're doing that on purpose so that you have a ability to see how wide the range of possible results is even with uncertainty in CO2.
- sien 6y ago
  From the article: "Correspondingly, the authors “recommend establishing a process for regular updates” to the scenarios and recommend that key variables in the scenarios “be updated now to be consistent with new historical data.”" So the author is explicitly saying different scenarios should be used, just that they should be updated regularly.

porb121 6y ago

moreover, plenty of scenario work predicts plenty of bad climate effects for rcps and ssps tighter than rcp8.5. by any estimation, the results of rcp8.5 would be disastrous.