Just as I thought I was out the ClimateBall Gods pull me back in. The “but RCP” flythe club got the best of me. For the time lost I found talking points for my Bingo. More on this project in due time. Here are the main ones:
- 8.5 is bollocks
- 8.5 is not BAU
- The IPCC calls 8.5 “BAU”
- The IPCC uses it as such
- Centuries or millennia separate 8.5 and when we might see 8.5W/m2
- We never were on an 8.5 path
- Only using 8.5 is bad science
- Without 8.5, there is no huge alarm
- Don’t present a < 1% scenario like the IPCC does
- It is not about blame
RCP stands for Representative Concentration Pathway. The acronym is usually followed with the numbers 2.6, 4.5, 6, or 8.5. Stating numbers will suffice in what follows. BAU stands for business-as-usual and IPCC for Intergovernmental Panel on Climate Change.
Now, for the experimental part of the post. One short paragraph for each talking point. I defer to ClimateBall authorities as much as I can. With your feedback I will revise the responses. I will also add secondary talking points in the comments.
One important caveat. “But RCPs” should not deflect from the main takeaway: global warming will continue until CO2 emissions reach zero. We will need to adapt to warming levels of 1.5C, likely more [Glen]. The answers start with a variation on the main take away, parry the contrarian deflection, correct the misleading information or the falsity, and repeat the main takeaway. A truth sandwich if you please, with a relevant salad, a clarifying soup, and a call to action dessert.
§1. It is common knowledge that getting to 8.5 is unlikely . It has been introduced to depict a relatively conservative business as usual case with low income, high population and high energy demand due to only modest improvements in energy intensity [Keywan & alii]. Things changed since 2011, and some might suggest that 3C is the new BAU. In effect, every dollar spent on mitigation now makes RCP8.5 emissions even more unlikely [Justin]. Scenario selection is not so important for impacts in the next decade or two [Glen]. If you don’t like 8.5, add 10 years [Gernot]. If you think that 8.5 is bollocks, well, that’s your unarticulated opinion.
§2. While 8.5 emissions are not BAU, the 8.5 concentration pathway can still arise from a lower emissions scenario if feedbacks are strong [Richard]. We also need to distinguish between emissions pathways and warming outcomes, which depend on emissions, carbon cycle feedbacks, and climate sensitivity [Zeke]. Without getting to net zero a radiative forcing of 8.5W/m2 will happen eventually [SteveE].
§3. It’s also important to call them “concentration pathways” as they’re named since over a decade ago, and to realise that over a decade ago it was already the extreme case with also bio-physical assumptions that differ from the other three RCPs. They never were “business as usual” [Joris]. Most climate modelling studies that use RCP8.5 are using the scenario in the form defined in terms of concentrations (the amount of CO2 & other GHGs bulding up in the atmosphere), not the form defined in terms of emissions (the amount humans are releasing) [Richard]. While the public and politicians at large discuss if and how we can get on a 2.6, to talk semantics about if we should rename “BAU” may be well intended, but is absurd [August].
§4. It would be incorrect to claim that the IPCC used 8.5 as BAU. First, 8.5 has a much faster rise in emissions than 1970-2010 [Richard]. Second, AR5 explicitly said “the term BAU has fallen out of favour because the idea of business as usual in century-long socio-economic projections is hard to fathom” [AT]. Scenarios without additional efforts to constrain emissions (’baseline scenarios’) lead to pathways ranging between 6.0 and 8.5 [IPCC]. Even the family of SSP5 baseline scenarios don’t all end up at 8.5 w/m^2 [Zeke].
§5. The idea that we might see 8.5W/m2 in centuries or millennia is bollocks. The remaining carbon budget in SSP5-8.5 is 7700 GtCO2, so 192 years of current emissions. If emissions increase, we reach it faster. Hence why it’s super important countries meet their Paris agreement commitments. For instance, in the high-end of the current policies estimates you’d get to 8.5 w/m^2 concentrations by 2150, assuming constant emissions of ~65 GtCO2 after 2100 [Zeke]. Its all based on MAGICC model runs. The 8.5 w/m^2 scenario being used in CMIP6 is the SSP5 REMIND Baseline [Zeke].
§6. While we may dispute the likeliness of getting to 8.5W/m2 in 2100, we are indeed in an 8.5 path [Kathryn]. Despite its long term aggressiveness, to date our cumulative emissions are closest to RCP 8.5 [Bob]:
§7. RCP8.5 is popular because trying it first is the best use of finite computational resources. If an effect can’t be found in 8.5, then there’s no point in trying the lower RCPs. However, if 2.6 is tried first, and there’s no effect, it says nothing about the higher RCPs [PaulW]. Anyone saying that 8.5 is a standalone forecast is at best in error; those who know the facts should be held to a higher standard [Bill].
§8. The fact remains that 5C is the baseline warming [Zeke]. Five degrees less is what separates us from the ice age [Gavin]. The claim that without 8.5 there is no “huge alarm” implies that *any” lower value would not be a huge alarm [me]. There will be ONE takeaway from this whole “but RCPs” thing, for most people in policy, business & media, and it will be this: “We can worry less about the effects of climate change!” Great work, guys. Really good stuff [Kate].
§9. If the IPCC could attribute a valid statistic to scenarios, they would make predictions, not scenarios. The that there is a 1% probability to 8.5 certainly doesn’t come from the IPCC [PaulS].
§10. Some may pretend that “but RCP” isn’t about blame. Yet they can’t prevent themselves from appealing to INTEGRITY, credibility or whatnot. (Examples on demand.) The following meme format should reveal how our usual suspects are squirreling with “but RCPs”:
- Tired – arguing about 8.5
- Wired – working toward 2.6 [Costa]
- Inspired – 2.6 is just a milestone, not a final goal [Jonathan]
- Bored – let’s just get a policy in place that seriously limits emissions and drives toward a broad international emissions trading system [Kevin].
Srsly, the obsession with RCPs is misplaced [mt]. Who cares about “but RCPs” if the conclusion is that we need to stop using fossil fuels no matter what scenario [Somite]. Getting to carbon zero is key in every way. In any event, those who still care about the “but RPCs” ClimateBall fight could take a look at Pietro’s synopsis: