{"id":739,"date":"2026-08-06T02:23:08","date_gmt":"2026-08-06T02:23:08","guid":{"rendered":"https:\/\/hackthemap.com\/?p=739"},"modified":"2026-08-06T02:23:08","modified_gmt":"2026-08-06T02:23:08","slug":"new-generation-of-climate-scenarios-shifts-high-end-warming-projections-downward-for-ipcc-seventh-assessment","status":"publish","type":"post","link":"https:\/\/hackthemap.com\/?p=739","title":{"rendered":"New Generation of Climate Scenarios Shifts High-End Warming Projections Downward for IPCC Seventh Assessment"},"content":{"rendered":"

Every six to seven years, climate modeling groups from around the globe embark on a coordinated set of simulations designed to explore how Earth’s climate could evolve over the coming decades and centuries. These rigorous simulations form a cornerstone of scientific evidence for the future projections featured prominently in the assessment reports produced by the Intergovernmental Panel on Climate Change (IPCC). Built around a common set of future pathways for greenhouse gas emissions, these models provide a crucial lens through which policymakers, scientists, and communities can anticipate environmental shifts.<\/p>\n

A completely new set of scenarios has now been published for the seventh phase of the Coupled Model Intercomparison Project, widely known as CMIP7. Detailing the framework in the journal Geoscientific Model Development, and releasing the underlying data into the public domain, researchers have established the pathways that will drive the next generation of climate models. These scenarios replace the shared socioeconomic pathways, or SSPs, that underpinned the previous generation of climate models and heavily influenced the IPCC’s sixth assessment report.<\/p>\n

\"Explainer:<\/figure>\n

The newly unveiled scenarios depart from their predecessors in several notable ways. Rather than bearing opaque names derived from specific radiative forcing levels, the new scenarios are labeled simply by their emissions trajectories, spanning from low-to-negative to high. They entirely discard the concept of no-climate-policy baseline worlds, choosing instead to explore the real-world implications of current policies continuing, strengthening, or weakening over time. Furthermore, the new framework dramatically revises high-end future emissions downward, dropping far below the peak scenarios of prior generations to reflect a modern energy landscape where a 21st century dominated by coal use is no longer plausible. At the same time, the lowest emissions scenarios have been revised upward relative to the sixth assessment cycle, making some degree of temporary overshoot of the Paris Agreement’s aspirational 1.5-degree Celsius warming target practically unavoidable.<\/p>\n

A New Generation of Scenarios and Updated Socioeconomic Storylines<\/h2>\n

To simulate how human actions will shape future climates, climate modelers estimate future levels of radiative forcings\u2014the external drivers that induce global warming, such as atmospheric concentrations of greenhouse gases, air pollutants, and land-use modifications. Because the future remains inherently uncertain, modelers rely on a handful of distinct scenarios spanning a wide range of plausible outcomes. The Scenario Model Intercomparison Project coordinates this complex development process for IPCC reports.<\/p>\n

\"Explainer:<\/figure>\n

The previous generation of SSP scenarios was beginning to show its age. Finalized between 2015 and 2017 using historical data ending in 2015, several years projected by those older scenarios were already in the past by the time the IPCC concluded its sixth assessment cycle in 2021. In the intervening years, the global energy system, economic conditions, and policy landscapes have shifted considerably.<\/p>\n

The most visible change in the new generation of scenarios is their nomenclature. Where the SSPs combined five distinct socioeconomic storylines with precise radiative forcing targets, the CMIP7 scenarios are named directly after the emissions trajectory they follow. Each scenario is underpinned by an updated set of socioeconomic storylines sharing conceptual roots with the original SSPs, incorporating assumptions regarding population growth, technological advancement, economic development, and international cooperation. These underlying socioeconomic assumptions received a comprehensive update with fresh population and economic projections.<\/p>\n

\"Explainer:<\/figure>\n

The updated socioeconomic data reveals a somewhat more crowded and less wealthy world per person than originally envisioned. Global population has been revised upward in nearly every scenario, with the middle-of-the-road pathway projecting a global population of 9.9 billion people by the year 2100\u2014an increase of one billion people compared to older projections. Meanwhile, gross domestic product was adjusted downward in high-end growth scenarios, slightly upward in regional rivalry and inequality-focused pathways, and left largely unchanged in middle-of-the-road trajectories. Consequently, income per person by the end of the century is projected to be roughly 10 to 25 percent lower in most scenarios.<\/p>\n

Another major structural shift involves the socioeconomic pathway underlying the highest future emissions scenario. In the previous generation, the very high scenario relied on a fossil-fueled development pathway, whereas the new high scenario in CMIP7 is based on a fragmented world characterized by regional rivalry and major challenges to adaptation. Integrated assessment modeling teams found that variants of these two pathways produced comparable emissions, but judged the fragmented regional rivalry world to be more relevant for exploring severe high-end climate risks.<\/p>\n

\"Explainer:<\/figure>\n

Elimination of Baseline Scenarios and Shifting Mitigation Pathways<\/h2>\n

In a departure from past modeling protocols, the authors of the CMIP7 scenarios eliminated traditional baseline scenarios that assumed a hypothetical world devoid of any climate policies. These old baselines were previously used as counterfactuals against which climate-altered worlds could be measured. Instead, the new suite begins with current policies and explores how those frameworks might be strengthened, weakened, or maintained.<\/p>\n

The high scenario now explores a plausible rollback of current mitigation policies. In contrast, the medium scenario extends climate policies officially implemented as of 2025, operating without the assumption that nations will fully achieve their nationally determined contributions under the Paris Agreement or meet net-zero targets not yet backed by binding domestic legislation. Scenario authors emphasize that this medium scenario should not be interpreted as a most likely prediction, but rather serves as a clear benchmark to measure the impact of future policy adjustments. <\/p>\n

\"Explainer:<\/figure>\n

The low scenario models a world where climate policy is rapidly intensified to limit end-of-century warming below two degrees Celsius. The very-low scenario aims to hold global warming to approximately 1.5 degrees Celsius by 2100, though it incorporates a greater degree of mid-century temperature overshoot due to the reality that global emissions did not begin rapidly declining in 2020 as earlier models had hoped. Furthermore, intermediate scenarios that transition from high emissions to rapid mitigation mid-century are designed to explore futures where climate action is initially delayed but aggressively accelerated later on.<\/p>\n

CMIP7 introduces several other vital technical enhancements. For the first time, climate models will be driven directly by emissions of carbon dioxide and other greenhouse gases rather than prescribed atmospheric concentrations. Models equipped with interactive carbon cycles are asked to run in emissions-driven mode, allowing them to calculate atmospheric concentrations dynamically based on emissions. This critical update ensures that substantial uncertainties regarding carbon-cycle feedbacks will propagate directly into the range of projected warming. Additionally, historical emissions are harmonized up to 2023, ensuring that scenario differences only open up after 2026 and preventing models from diverging from reality before simulations even begin. The simulation timeline has also been extended from 2100 to 2150 to provide a more comprehensive look at the lifetime exposure of future generations, with long-term extensions reaching out to 2500 to evaluate ice sheets, sea-level rise, and climate reversibility.<\/p>\n

\"Explainer:<\/figure>\n

Narrower Emissions Ranges and the Downward Shift in High-End Warming<\/h2>\n

Overall, the new scenarios compress the range of future carbon dioxide emissions compared to the sixth assessment generation. At the lower end, the trajectories closely mirror their predecessors, with the very-low scenario reaching net-zero carbon dioxide emissions around mid-century. However, cumulative emissions in these low scenarios are somewhat higher over the 2024-2100 period because the world missed the opportunity for immediate post-2020 emission cuts.<\/p>\n

The most dramatic transformation occurs at the high end of the spectrum. While previous extreme scenarios assumed massive coal expansion throughout the 21st century, the new high scenario reaches 55 gigatons of carbon dioxide per year in 2100, compared to the roughly 126 gigatons projected by older extreme pathways. In cumulative terms, the new high scenario generates about 3,820 gigatons of carbon dioxide between 2024 and 2100, which is roughly half of the emissions load projected by the previous extreme fossil-fueled baseline.<\/p>\n

\"Explainer:<\/figure>\n

This downward revision stems from two major developments over the past decade. First, rapid advances in cheap solar, wind, and battery technologies, combined with trillions of dollars in annual clean-energy investments and a global plateau in coal demand, have rendered a total rollback of climate policy to extreme fossil fuel deployment implausible. Second, the adjustment reflects better communication regarding the nature of scenarios; past extreme pathways were intended as worst-case bounds rather than expected trajectories, and real-world clean energy deployment has significantly altered the baseline outlook.<\/p>\n

When run through standardized climate model ensembles, the seven CMIP7 scenarios yield a median warming in 2100 relative to pre-industrial levels ranging from 1.6 degrees Celsius in the very-low scenario to 3.3 degrees Celsius in the high scenario, with the current-policy medium scenario reaching 2.9 degrees Celsius. Under the medium scenario, passing the 1.5-degree threshold becomes locked in by the early 2030s, the two-degree limit is crossed around mid-century, and the chance of exceeding four degrees Celsius rises if emissions persist beyond 2150. Conversely, lower emissions scenarios require substantial atmospheric carbon removal to achieve peak and decline temperature profiles.<\/p>\n

\"Explainer:<\/figure>\n

The Scale of Carbon Dioxide Removal<\/h2>\n

Achieving global warming peaks and subsequent declines requires pulling carbon dioxide back out of the atmosphere to prevent millennial-scale warming persistence. Every deep mitigation scenario in CMIP7 incorporates significant amounts of carbon dioxide removal, spanning both land-based sinks and engineered technologies such as bioenergy with carbon capture and storage, direct air capture, enhanced rock weathering, and biochar.<\/p>\n

The low-to-negative scenario requires pulling a cumulative 2,360 gigatons of carbon dioxide out of the atmosphere by 2150. Even the very-low scenario, which seeks to minimize reliance on removal technologies, demands 655 gigatons of net removals between 2024 and 2150. The extent to which these scenarios depend on engineered geological storage versus biological land sinks varies widely across models, with some pathways relying heavily on direct air capture units that could capture billions of tons annually by the end of the century. <\/p>\n

\"Explainer:<\/figure>\n

Deploying carbon removal at this unprecedented scale would necessitate planetary-scale engineering costing trillions of dollars, presenting significant technological, economic, and logistical challenges. Nevertheless, as modeling groups begin running the full suite of CMIP7 Earth-system simulations, these updated scenarios will provide the vital foundation for the IPCC seventh assessment cycle, guiding governments, industries, and societies as they navigate the realities of a warming world.<\/p>\n","protected":false},"excerpt":{"rendered":"

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