The Dangerous Optimism of Climate Scenarios: The Reality Lost Between RCP 8.5 and RCP 2.6

In April 2026, the IPCC formally declared that RCP 8.5, one of the most debated scenarios in climate science, is no longer realistic. According to the report, the rapid growth of renewable energy and the partial transformation brought about by climate policies have made the highest-emissions pathway increasingly unlikely. For many observers, the announcement was reassuring news. Yet there is reason to be cautious about that sense of relief. The same report also quietly acknowledged that RCP 2.6—the pathway designed to keep global warming below 2°C—may no longer be realistic either. Taken together, these two statements reveal a profound contradiction at the heart of climate science today.

The retirement of RCP 8.5 is partly welcome news. Coal consumption is unlikely to rise to the levels assumed by that scenario, and renewable energy has expanded much faster than many expected. However, it is important to distinguish between emissions pathways and temperature outcomes. The fact that RCP 8.5 is becoming implausible as an emissions scenario does not mean that the temperatures associated with that scenario are no longer possible.

Climate models generally treat the climate system as largely linear and predictable. In reality, however, the Earth system contains thresholds that, once crossed, can trigger self-reinforcing and irreversible changes. These tipping points include the collapse of the West Antarctic Ice Sheet, the transformation of the Amazon rainforest into savanna, the shutdown of the Atlantic Meridional Overturning Circulation (AMOC), and the release of vast stores of carbon from thawing permafrost. Such processes are often only partially represented in climate models and are sometimes omitted altogether. More importantly, tipping points may interact with one another, creating cascading effects that could accelerate warming far beyond current expectations.

The consequence is significant. Even if humanity does not follow the RCP 8.5 emissions pathway, climate feedbacks and tipping-point dynamics could still push the planet toward temperature outcomes comparable to—or even exceeding—those associated with RCP 8.5. In that sense, RCP 8.5 may no longer be plausible as an emissions scenario, but it remains plausible as a temperature outcome. This distinction is not emphasized strongly enough in climate communication, and that omission carries risks.

At the same time, the IPCC has been reluctant to make an equally clear statement about RCP 2.6. The reasons are partly scientific but also institutional and political. Current Nationally Determined Contributions (NDCs) remain far from the reductions required to achieve the RCP 2.6 pathway. Furthermore, the scenario relies heavily on negative-emissions technologies capable of removing carbon dioxide from the atmosphere at an enormous scale. Today, the combined capacity of all such facilities worldwide remains less than one-thousandth of what would be needed. This is not a minor engineering challenge; it suggests that the scenario itself is increasingly disconnected from real-world developments.

Declaring RCP 2.6 implausible would effectively amount to admitting that the internationally recognized 1.5°C and 2°C targets are no longer achievable. The political implications of such a statement are profound, and the IPCC has understandably been reluctant to take that step. As a result, the range of plausible futures has narrowed from both ends, yet only the contraction on the pessimistic side has been publicly highlighted. Scientific transparency would require equal honesty about both developments.

None of this is meant as a criticism of the IPCC. Its reports represent the collective work of thousands of scientists and remain the most authoritative assessments of climate science available. However, the institution operates through consensus, and consensus tends to favor caution. The most controversial and alarming findings face the highest evidentiary threshold before they can be included. As a result, IPCC assessments have historically leaned toward conservative estimates.

The career of climate scientist James Hansen provides a striking example. His projections presented to the U.S. Congress in 1988 were often dismissed as alarmist. Yet many of those projections proved remarkably accurate. Arctic sea-ice decline, sea-level rise, and the intensification of extreme weather have frequently unfolded at rates that match or exceed mainstream expectations. Looking back, the pattern is difficult to ignore: observed changes often evolve toward the more severe end of the projected range.

This suggests that IPCC reports should perhaps be viewed not as worst-case scenarios but as optimistic-realistic scenarios. Many tipping-point processes remain poorly represented. Large-scale carbon removal technologies remain largely hypothetical. Institutional caution can make it difficult to fully incorporate the most concerning possibilities. For these reasons, the future that ultimately unfolds may prove more severe than the futures most prominently discussed today.

This reality brings us to one of the oldest debates in climate policy: mitigation versus adaptation. In truth, this dilemma is a false choice. Both are indispensable. Reducing greenhouse-gas emissions remains essential because less warming inevitably means fewer impacts. Every tonne of carbon dioxide avoided is important. Yet the current trajectory of global climate policy, combined with uncertainties surrounding tipping points and carbon-removal technologies, means that adaptation can no longer be treated as a secondary concern.

For a country such as Türkiye, adaptation is increasingly a necessity. The Mediterranean region is warming roughly 1.5 times faster than the global average. Water stress is intensifying, agricultural systems are becoming more vulnerable, wildfire risks are growing, and rising sea levels threaten coastal communities. Under such conditions, adaptation is not a backup plan; it is a central component of climate strategy.

The logical conclusion is straightforward. We must do everything possible to slow climate change while simultaneously preparing for its worst consequences. These goals do not conflict with one another; they reinforce one another. Much of the climate change that will shape the coming decades is already built into the system. Recognizing this fact does not mean being pessimistic. It is an act of realistic planning.

The retirement of RCP 8.5 while RCP 2.6 remains officially alive represents a significant shift in climate communication. It reflects the tension between the desire to deliver reassuring messages and the obligation to communicate scientific realities. Yet the climate system itself is indifferent to political narratives. Tipping points do not respond to diplomatic language. Permafrost does not wait for negotiation schedules.

The prospect of hosting COP31 in Antalya makes this discussion especially tangible. Antalya is not an abstraction. It is a place where forests burn, agricultural lands become drier, seas warm, and rainfall becomes increasingly extreme. Any honest assessment of climate risk from this region must consider not only what climate scenarios explicitly show, but also what they may leave out.

Ultimately, the path forward is clear. Humanity must continue pursuing the fastest possible reductions in greenhouse-gas emissions while preparing societies, economies, and ecosystems for a future that may be more disruptive than many current projections suggest. These are not competing priorities. They are two sides of the same responsibility.