Assessing whether a scenario is plausible or not requires evaluating whether the assumptions involved in its development are reasonable. For example, we know that extreme scenarios are implausible because they predict that the global energy system will "return to coal," requiring a massive expansion of global coal consumption. This has not happened and will not happen in the foreseeable future.

In 2000, the Intergovernmental Panel on Climate Change (IPCC) clarified that the development of reasonable scenarios begins with the assessment of socio-economic assumptions as the first step in a sequential process that ends with the outcomes of the climate model. But when scenarios were developed, social and economic assumptions were separated from climate model inputs, a blunder that allowed the extreme emissions scenario to become the focus of climate research and policy.

To be sure, the climate science community will not repeat again in 2024 the mistake of separating reasonableness from scenario selection and prioritization. Isn't it? But in fact that's exactly what happens. The climate science community is now calling for the creation of a new family of emissions scenarios to replace the old ones, but with regional economic programs separated from basic socioeconomic scenarios just as they did with old scenarios. Questions about the reasonableness and consistency of the scenario are left to the future.

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One step is to separate exploratory scenarios of interest to the modeling community from those relevant to the needs of policymakers. Science-focused scenarios should be described as exploratory, so as not to confuse scientific exploration with its policy importance. Of course, assertions about the importance of science-focused scenarios provide a compelling justification for funding and a role for modelers in climate policy. Although the earth system modelers claimed that reasonableness should be evaluated by others, they are still engaged in ad hoc reasonableness justifications, in the complete absence of any analysis. Part of their justification for prioritizing policy extreme emissions scenarios is as follows: The scenario includes events and outcomes that may not be possible given current trends but are still reasonable enough for them to occur. The worldview it represents is consistent with policy regression, lack of coordination and cooperation to address global environmental concerns, societies and industries that depend on and even return to fossil fuel resources, the adoption of resource- and energy-intensive production technologies and lifestyles, and unexpected technological barriers. This scenario is not intended to represent a "business as usual" scenario or a no-reference policy scenario for other cases. The scenario aims to explore the upper limit of greenhouse gas emissions resulting from a profound political, technological and structural deviation from current trends. It may be interesting and interesting, but exploring the climate consequences of a "profound political, technological, and structural deviation from current trends" – all in a negative direction – is less important to policymakers than scenarios that explore the direction we think we are already heading in the coming years and decades.

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The real justification for extreme scenarios here is, of course, not politics, but the extreme scenario allows for fascinating research, as it allows a direct comparison between the new generation of environmentally sound management tools and environmentally sound management units of the previous generation, and also allows the study of the signal-to-noise ratio of expected changes in climate to identify the characteristics of the climate system. But even better is to return to the IPCC report approach (2000) that avoided provisions on scenario probability and simply produced a very wide range of reasonable futures contracts, conditioned on alternative options and development paths. The future is a wide open place, and where we go is up to us. Few people realize that the next few decades of climate science – and therefore research-reviewed research, media coverage, climate advocacy, and climate policy – are now being determined by a very small group of researchers, with a very narrow scope of specialized expertise, without any expertise. Basic research on the reasonableness or usefulness of a scenario in decision-making, almost all from wealthy parts of the world, particularly the United States, the United Kingdom, and Europe.

Climate scenarios have evolved to have important roles in decisions that affect everyone on the planet. Scenarios are too important to leave to a dedicated group of researchers to design to serve their research, and a new approach is needed, and quickly. We are on the cusp of replacing another scenario, with the same negative consequences for research and policy and for the next decade or more. Can we change course before it's too late?