THREAD: Are emission scenarios useful (& for whom)?

A hard hitting & useful commentary on emission scenarios. Written in 2008, but the issues remain the same...

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https://iopscience.iop.org/article/10.1088/1748-9326/3/4/045016/meta

Global change's high stakes and deep uncertainties make the value of scenarios here clear, but their use is complicated by large structural differences between global change and other decision domains where use of scenarios is more thoroughly established and studied.

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[P]otential users of global-change scenarios are vast in number and in the variety of their responsibilities, knowledge, objectives, capabilities, and authority.

In many cases, relevant decisions and users are unidentified or unknown to those creating scenarios.

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[Scenarios] can attract widespread public attention, framing the issue & encoding its basic character & severity in public debates.

They thereby escape their creators' control, e.g., in being put to uses their creators did not foresee and cannot influence, ...

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Although scenarios could serve diverse decisions by focusing on many environmental or socio-economic conditions, they usually highlight emissions and modeled climate change, the elements that assessments specifically need.

[that is, scenarios are designed for assessments]

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Even when scenario exercises have begun with narrative scenarios, these have faded in significance as the exercise proceeded.

[Exactly what is happening to the SSPs...]

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While experience in other domains suggests users want scenarios to include uncertainties that can only be represented in qualitative or narrative terms, the weak relationship to particular users means that such preferences find little voice in global-change scenario exercises

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[T]he connections of scenarios to practical decisions managing global-change issues have been weak & indirect.

This reflects no particular failure of scenario efforts, as it follows from the primary use of scenarios in assessments...

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[To make scenarios more useful] it is first necessary to disaggregate...three types of decision-makers:
1. impacts and adaptation managers,
2. national officials,
3. energy resource and technology managers.

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A particularly controversial area for such transparency is the uncertainty judgments that underlie the presentation of a set of scenarios.

Developers commonly present a few scenarios with no information about their judgments of associated probabilities.

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Scenario teams have declined to answer even such seemingly simple questions as whether they judge emissions more likely to lie in the middle than at the ends of the envelope of all scenarios, & how likely they are to lie outside the envelope entirely.

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[T]hey have characterized the meaning of scenarios in opaque terms, e.g., that scenarios in a set are 'all plausible' or 'equally sound'.

This approach has been criticized for concealing probabilistic reasoning that must underlie the decision to identify a scenario...

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Global-change scenarios are controversial because they are powerful public framers of the issue, and because they act as proxies for the need to take action.

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Political actors with strong views on desired action have an interest in attacking scenarios that challenge their preferred course.

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Consequently, opponents of emission limits attack high-growth scenarios as biased or unrealistic & highlight low-growth ones, while proponents of limits do the opposite.

[Hmmm, so those of us that think RCP8.5 is bollocks are against emission limits?]

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It is easy to attack a scenario, by selecting one scenario in isolation, exaggerating its predictive intent, describing it as 'speculative' or 'unscientific', & digging into its details to find elements that appear implausible or erroneous—which can usually be found.

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[A] more effective & honest response requires re-focusing on sets of scenarios to represent key uncertainties, explaining that such assumptions are required for responsible decision-making under uncertainty

[Though, we are going overboard on model inter-comparisons now?]

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[A]nd—hardest of all—conveying that calling scenarios 'speculative' or 'unscientific' is correct, but beside the point.

[This is interesting, modellers should admit their scenarios are crap, but argue they are still useful]

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[Scenario analysis] is an approach that seeks to make speculation more disciplined, more anchored to scientific knowledge where it is available, and more transparent, which is essential to informing global-change decision-making.

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A good commentary. It is a lot of deja vu: it is critiquing scenario processes of the past, but the critique applies equally well to scenario processes of today.

Key lessons not learnt? Or is the scenario community where it wants to be (framing the policy debate)?

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