Thou Shalt Use RCP8.5

Governments are mandating the use of outdated climate scenarios as scientists stand by silently

Let us leave RCP8.5 behind, but please, not yet.

In 2010, the North Carolina Coastal Resource Commission issued a report recommending that the state use a range of 0.4 to 1.4 meters of sea level rise to 2100 for official planning purposes. Some thought the scenarios underlying this range were too extreme and appealed to the North Carolina legislature to take action.

In response, the state Senate drafted a bill that would mandate the methodologies and time frame for climate scenarios developed to inform state regulation and policy making. The response among scientists and beyond, understandably, was outrage.

Comedian Stephen Colbert quipped:

If your science gives you a result you don't like, pass a law saying the result is illegal. Problem solved.

As a result of the widespread criticism, the bill was watered down when it reached the North Carolina House, but the final legislation still contained directives for how scenarios for sea level rise should be developed.

I was reminded of this episode upon learning today that the Dutch government has once again adopted our old friend RCP8.5 as a “plausible” scenario for planning and policy. The 2023 official Dutch government scenarios — called the KNMI National Climate Scenarios 2023 for the Netherlands — were previously developed in 2006 and 2014, meaning that the new 2023 scenarios will inform Dutch policy making into the early 2030s.

The choice to emphasize SSP5-8.5 is mystifying as the Netherlands has some of the world’s leading climate scientists and scenario experts who know better.

Let’s take a quick look at the details.

KNMI, the Royal Netherlands Meteorological Institute, lists plausibility as the first criterion of several in its selection of scenarios to inform policy:

The KNMI’23 scenarios are designed to provide a scientific set of plausible, (internally) consistent and relevant future climate conditions, to be used as a reference framework for a multitude of societal impact assessments of different scope and origin.

KNMI justifies its emphasis on two scenarios, SSP5-8.5 and SSP1-2.6, as follows:

We choose as upper and lower bound of projected global climate change (and associated global temperature change as the driver of regional climate change) a scenario for sustainable development (SSP1-2.6) and a scenario for fossil-fuel intensive development (SSP5-8.5).¹

Readers here will well understand that SSP5-8.5 — the updated version of RCP8.5 — is not a plausible scenario, and this understanding has a broad and growing consensus within the scientific community.

KNMI compounds their problems by characterizing the difference between the 8.5 and 2.6 scenarios as indicative of the benefits of climate mitigation, indicating that 8.5 is a reference scenario and 2.6 is a policy scenario:

We opted for a large bandwidth between the KNMI’23 high and low emission scenario to emphasize the consequences of the international choices of mitigation policies, and to have a framework for national risk assessments.

The U.N. Framework Convention on Climate Change, the Intergovernmental Panel on Climate Change, a wide range of peer reviewed research and the global scenario community are all in agreement that on current policies, the world is tracking below a SSP2-4.5 scenario.

KNMI further attempts to justify its prioritization of SSP5-8.5, and in the process makes multiple false claims and engages in a bit of plagiarism:

SSP5-8.5 is the highest emission scenario and serves as a benchmark of no mitigation of climate change at all, although many countries have already implemented mitigation measures. Hence, the SSP5-8.5 pathway should be considered as an upper bound of greenhouse gas emissions. It can be useful for risk analyses in the context of climate adaptation in the sense of the precautionary principle. In the scientific literature the plausibility of SSP5-8.5 is debated (Hausfather and Peters, 2020). Some researchers argue that SSP5.8.5 could be more likely than was originally proposed. This is because some important feedback effects — such as the release of greenhouse gases from thawing permafrost (Friedlingstein et al., 2014; Lenton et al., 2014) might be much larger than has been estimated by current climate models.

The false claims and plagiarism in short:

• SSP5-8.5 is not a plausible “upper bound” on future emissions levels. Based on current policies, such an upper bound would be below the emissions trajectory of SSP2-4.5.

• KNMI conflates a plausible scenario for policy planning with a stress-test scenario for precautionary risk assessment — SSP5-8.5 is neither.

• Hausfather and Peters (2020) is miscited and plagiarized.

  • Hausfather and Peters (2020) do not support a debate over over SSP5-8.5 plausibility. In fact, they claim the opposite: “Happily — and that’s a word we climatologists rarely get to use — the world imagined in RCP8.5 is one that, in our view, becomes increasingly implausible with every passing year.”

  • KNMI sloppily plagiarizes text verbatim from Hausfather and Peters (2020):

    • “Some researchers argue that SSP5.8.5 could be more likely than

      was originally proposed. This is because some important feedback effects — such as the release of greenhouse gases from thawing permafrost (Friedlingstein et al., 2014; Lenton et al., 2014) might be much larger than has been estimated by current climate models.”

    • But KNMI failed to acknowledge the text that followed: “Yet, in our view, reports of emissions over the past decade suggest that they are actually closer to those in the median scenarios. We contend that these critics are looking at the extremes and assuming that all the dice are loaded with the worst outcomes.”

    • This is really poor — plagiarism and reversing the meaning of the borrowed text. KNMI will want to investigate their quality control processes.

UPDATE: KNMI in De Telegraaf says that they do not want to make the more plausible SSP2-4.5 available to the public out of concerns that the public will see it as more plausible:

“We don't want people to take the intermediate scenario as a prediction from the KNMI”

That is incredible.

I could go on. I won’t.

The “new” Dutch climate scenarios are not unique. The governments of the United States, United Kingdom, New Zealand, the European Union and surely many others have formally recommended or mandated the use of extreme, implausible climate scenarios — that is, RCP8.5 or SSP5-8.5 — in policy planning and regulatory decision making.

I’m not going to mince words — In 2023, giving RCP8.5 official governmental status is scientific and policy malpractice. It will lock-in the use of an implausible climate scenario for the rest of the decade, even as climate experts know better.

A decade ago, when elected officials in North Carolina sought to institutionalize incomplete and flawed science related to climate scenarios, the scientific community pushed back loudly and publicly. In contrast, today as governments seek to institutionalize flawed and incomplete science related to climate scenarios, elements of the scientific community are complicit in promoting the flawed science. More broadly, the entire community has thus far remained silent as they watch governments and multi-lateral institutions promote outdated scenarios.

I can’t say I really understand this — we all should want governments to use the best available and most up-to-date understandings to guide decision making. Perhaps there is a concern that resetting our thinking on scenarios will result in major changes in how we think about climate and climate policy, as the reliance on extreme scenarios has been a staple of climate politics for decades.

But make no mistake, change will come. Just not yet.

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1. In the report KNMI states that it also includes SSP2-4.5 at the request of stakeholders. Whether the users of scenarios can simply ignore SSP5-8.5 and substitute SSP2-4.5 remains to be seen.