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> Most recent IPCC commentary on predictions to underscore that current estimates land in a range, and that the Guardian-cited source is not in the middle of it

> Most recent IPCC commentary on predictions to underscore that current estimates land in a range, and that the Guardian-cited source is not in the middle of it Could you quote which part you are referring to? If you look at the IPCC Sixth Assessment Report, it predicts for Shared Socioeconomic Pathway SSP2-4.5 (the middle of the options presented, "CO2 emissions around current levels until 2050, then falling but not reaching net zero by 2100") warming of 2.7C by 2100. 2.9C is not an extreme prediction at all.

timr 4y ago
2.9C is absolutely an extreme prediction. The figure I linked is from the IPCC SR15 (source was in the comment). Digging through the sixth assessment report, there's this: https://www.ipcc.ch/report/ar6/wg3/static/4d357606f10734acb37dc3c49dd4a32c/a8441/IPCC_AR6_WGIII_FigureSPMBox.png https://www.ipcc.ch/report/ar6/wg3/static/4d357606f10734acb3... You can see that 5/8 of the projections fall below 2.5C, and 4/8 fall below 2C. The predictions that rise above 2.5C are the three most extreme categories of the report. There's simply no way to claim that a prediction of 2.9C is not "extreme". SSP2-4.5 is in category C6, which is the top 50% of all predictions. Moreover, from the report describing the "categories": > Around half of all modelled global emission scenarios assume cost-effective approaches that rely on least-cost emission abatement options globally. The other half look at existing policies and regionally and sectorally differentiated actions So you're talking about a distribution of predictions where half assume little/no changes over current circumstances. The problem with all of these scenario "categories" is that they're bucketed by maximum predicted temperature, so it all becomes a game of begging the question: if you choose to emphasize "category C7" from the IPCC report, it means only that you prefer to believe a scenario where warming tops out at 4C (literally the definition of C7). Scenarios that make wildly different assumptions are grouped together, and it's impossible to know which ones are likely, and difficult to know which ones reflect current planned mitigations, etc. But this does show clearly the range of possible predicted outcomes -- if some newspaper comes along and tells you that "experts" are "predicting" a rise of 4C, you can know that they're on the tail of the distribution of reasonable predictions. Edit: found the description of SSP2-4.5 (table SPM.2, here [1]). It assumes that we never hit net zero CO2 production, and that GHG emissions continue on their current path through 2050 with only minimal mitigatons. Is this realistic? Who knows. But it's certainly not the stated plan. [1] https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_SPM.pdf https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6...
- arbitrary_name 4y ago
  Given that the IPCC projections have been consistently conservative, and have been revised upward repeatedly, i personally do not consider 2.9 an extreme value. >It assumes that we never hit net zero CO2 production, and that GHG emissions continue on their current path through 2050 with only minimal mitigatons You mean...the path we are basically on, and have been on, since decades despite knowing the consequences? "Not the stated plan" is doing a lot of lifting here.

timr 4y ago

2.9C is absolutely an extreme prediction. The figure I linked is from the IPCC SR15 (source was in the comment). Digging through the sixth assessment report, there's this: https://www.ipcc.ch/report/ar6/wg3/static/4d357606f10734acb37dc3c49dd4a32c/a8441/IPCC_AR6_WGIII_FigureSPMBox.png https://www.ipcc.ch/report/ar6/wg3/static/4d357606f10734acb3... You can see that 5/8 of the projections fall below 2.5C, and 4/8 fall below 2C. The predictions that rise above 2.5C are the three most extreme categories of the report. There's simply no way to claim that a prediction of 2.9C is not "extreme". SSP2-4.5 is in category C6, which is the top 50% of all predictions. Moreover, from the report describing the "categories": > Around half of all modelled global emission scenarios assume cost-effective approaches that rely on least-cost emission abatement options globally. The other half look at existing policies and regionally and sectorally differentiated actions So you're talking about a distribution of predictions where half assume little/no changes over current circumstances. The problem with all of these scenario "categories" is that they're bucketed by maximum predicted temperature, so it all becomes a game of begging the question: if you choose to emphasize "category C7" from the IPCC report, it means only that you prefer to believe a scenario where warming tops out at 4C (literally the definition of C7). Scenarios that make wildly different assumptions are grouped together, and it's impossible to know which ones are likely, and difficult to know which ones reflect current planned mitigations, etc. But this does show clearly the range of possible predicted outcomes -- if some newspaper comes along and tells you that "experts" are "predicting" a rise of 4C, you can know that they're on the tail of the distribution of reasonable predictions. Edit: found the description of SSP2-4.5 (table SPM.2, here [1]). It assumes that we never hit net zero CO2 production, and that GHG emissions continue on their current path through 2050 with only minimal mitigatons. Is this realistic? Who knows. But it's certainly not the stated plan. [1] https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_SPM.pdf https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6...

arbitrary_name 4y ago
Given that the IPCC projections have been consistently conservative, and have been revised upward repeatedly, i personally do not consider 2.9 an extreme value. >It assumes that we never hit net zero CO2 production, and that GHG emissions continue on their current path through 2050 with only minimal mitigatons You mean...the path we are basically on, and have been on, since decades despite knowing the consequences? "Not the stated plan" is doing a lot of lifting here.