Why the worst-case climate scenario was revised, not discarded

Recent discussions surrounding climate scenarios, particularly the purported "폐기" (discarding) of the worst-case scenario, have been met with misleading interpretations. US President Donald Trump, for instance, claimed on social media that the UN's top climate body admitted its predictions were wrong. Similarly, a conservative domestic media outlet suggested that experts, media, and environmental activists had accepted extreme scenarios as plausible future realities without critical review.

However, these interpretations misrepresent the nature of climate scenarios. The Intergovernmental Panel on Climate Change (IPCC), the UN body for climate science, updates its scenarios with each report. The scenarios used in the 5th (2013) and 6th (2021) assessment reports differed, moving from Representative Concentration Pathways (RCPs) to Shared Socioeconomic Pathways (SSPs). The SSP framework incorporates socioeconomic contexts alongside greenhouse gas emissions, acknowledging the impact of human response to climate change.

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The UN's top climate committee just admitted that their predictions were wrong! Wrong! Wrong! Wrong!

The shift away from the most extreme scenario (SSP5-8.5) is not an admission of error but a reflection of evolving circumstances. In the early 2010s, when SSP5-8.5 was first introduced, global greenhouse gas emissions were rapidly increasing, renewable energy was expensive, and electric vehicles were nascent. Under those conditions, projections of continued fossil fuel use throughout the century seemed plausible. However, the dramatic decrease in renewable energy costs and the significant reduction in fossil fuel consumption have rendered such extreme pathways less likely.

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Scenarios should encompass plausible outcomes from high to low levels. This range will narrow compared to what was assessed in the past.

The authors of the relevant paper explain this change by stating that scenarios "should encompass plausible outcomes from high to low levels. This range will narrow compared to what was assessed in the past." They note that "the high-emission level (SSP5-8.5) has become less plausible" due to falling renewable energy costs, the emergence of climate policies, and recent emission trends. They also acknowledge that some low-emission trajectories no longer align with observed trends, suggesting a need to revise the most optimistic scenarios as well.

Therefore, the revision of scenarios is an adaptation to scientific and policy developments, not a refutation of scientific accuracy. The decrease in the projected severity of climate change is largely attributable to international cooperation, such as the Paris Agreement, which has demonstrably lowered projected global temperature increases. While progress has been made, the gap between current commitments and the 1.5-degree target remains, indicating that complacency is unwarranted.

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The high-emission level (SSP5-8.5) has become less plausible due to the downward trend in renewable energy costs, the emergence of climate policies, and recent emission trends.