The Truth Behind Climate Activist’s Favorite Model

In late April, the United Nations Intergovernmental Panel on Climate Change (IPCC) finally described Representative Concentration Pathway 8.5 — commonly known as RCP8.5 — as an “implausible” emissions pathway.

This long-overdue admission should have triggered a broad reassessment across climate science and policymaking. For more than a decade, RCP8.5 was routinely presented as a standard “business-as-usual” future in which global temperatures would climb more than 4.3°C by 2100. Those projections were then used to warn of catastrophic economic, environmental, and social consequences.

The scenario also heavily influenced international climate negotiations. Governments faced repeated calls for new treaties, stricter regulations, and rapid cuts in fossil fuel use, often justified by the claim that the world was otherwise headed straight toward RCP8.5’s extreme emissions levels.

Concerns about the scenario were hardly new. Researchers had warned for years that it was highly improbable and should never be treated as the expected outcome. Still, RCP8.5 continued to appear in peer-reviewed studies, media reports, policy discussions, legal cases, and public advocacy. It was frequently framed not as a remote worst-case possibility, but as the likely result of failing to enact aggressive climate policies.

Critics had raised alarms much earlier. The Heartland Institute highlighted problems with RCP8.5 as far back as 2017, describing it as not merely unlikely but potentially impossible. A more detailed analysis followed in the 2019 publication Climate Change Reconsidered II: Fossil Fuels.

Unfortunately, the admission arrived only after RCP8.5 had already shaped an enormous volume of research. By early 2020, roughly 20 studies per day were being published that relied on the scenario. Estimates suggest more than 8,500 papers using RCP8.5 appeared over an 18-month span.

Clear reasons existed from the start to question its realism. The pathway assumed global coal consumption would rise about fivefold by 2100 — a level critics argued might exceed available economically recoverable reserves. It also incorporated population projections far higher than current forecasts, including the possibility of 12.6 billion to 14.5 billion people worldwide by century’s end, trends that current data do not support.

Despite these weaknesses, RCP8.5 became deeply embedded in climate research and public policy. What is now being treated as a fresh insight was, according to long-standing critics, already understood by many participants in the debate years earlier. Instead of being retired or clearly labeled as an extreme hypothetical, the scenario served as the foundation for studies, laws, regulations, financial decisions, court cases, educational materials, and public messaging.

This pattern points to a deeper problem in the relationship between science, advocacy, and politics. The late climate scientist Stephen Schneider once described the difficult balance researchers face: they are expected to communicate risks with full honesty about doubts and uncertainties, yet those seeking political action often feel pressure to simplify messages, emphasize alarming outcomes, and minimize uncertainty to capture public and media attention.

That tension becomes problematic when advocacy overrides scientific caution. Science relies on openness, skepticism, and acknowledgment of uncertainty. Presenting worst-case possibilities as probable outcomes for political reasons ultimately damages public trust.

The American Energy Institute recently launched the website They-Knew.com to document how RCP8.5 was used by governments, advocacy organizations, educators, courts, financial institutions, and others. The site aims to create a public record of these applications.

Its creators argue that researchers had already identified the scenario as unrealistic in major scientific journals years earlier, yet institutions continued relying on it anyway. They view this continued use, even after its shortcomings were widely known, as a significant failure of scientific integrity.

The website also highlights organizations and public figures who invoked RCP8.5 to support specific laws, regulations, and economic policies. Critics link those policies to consequences such as job losses, increased public debt, wasted resources, higher energy costs, and reduced consumer choice.

Perhaps the most troubling impact has been psychological. Projections based on RCP8.5 were often presented to children as describing an almost certain future. Many young people came to believe the world was heading toward environmental collapse because of their families’ energy use, contributing to widespread anxiety, guilt, anger, and fear about the future.

Now that RCP8.5 is increasingly recognized as implausible, the institutions that relied on it should reexamine the conclusions they reached. Research heavily based on the scenario deserves review, with its assumptions clearly disclosed. Policymakers should assess whether treaties, regulations, and programs were grounded in realistic projections or in an extreme scenario that was never likely to materialize.