Climate change’s worst-case scenario is officially canceled

You’ve probably never heard of the term “RCP 8.5” — the highest-emission scenario used by climate scientists to project the planet’s future. But if you’ve read about climate change, you’ve seen the numbers and nightmarish outcomes it produced: 4°C of warming by 2100, sometimes 5°C, sea level rising multiple feet, parts of the planet too hot for humans.

Those numbers shaped a decade and a half of climate journalism, including a lot of my own when I covered climate change at Time magazine. I didn’t always know — and didn’t always communicate — that the scenario behind the most apocalyptic, attention-getting findings was largely an attempt to imagine how bad things could get, not a true forecast. But I wasn’t alone. RCP 8.5 was a frequent background presence in climate journalism.

Last month, though, the scientists who built that scenario formally retired it. In a paper published in Geoscientific Model Development, Detlef van Vuuren and more than 40 co-authors eliminated RCP 8.5 from the scenarios that will feed into the Intergovernmental Panel on Climate Change’s (IPCC) Seventh Assessment Report, which is due in 2029. Based on falling clean-energy costs, climate policy, and recent emissions trends, the highest-emissions pathway had become, in their words, “implausible.”

I can understand if your eyes began glazing over as soon as you read “seventh assessment report,” but this shift represents real progress and hope. It means that the apocalyptic climate change future that we’ve been describing for 15 years is officially no longer on the table. Instead, a merely bad climate future — about 2.8°C by 2100 — is now the central scientific estimate. Given how hopeless our climate future has appeared at times, that really does qualify as good news.

Climate models can’t tell you the future on their own, because how much the planet will warm depends in large part on what humans do. So scientists build scenarios: structured guesses about how the next century might unfold under different assumptions about energy use, growth, and climate policy.

Four such scenarios were introduced in 2011 as the standard set for the IPCC, the international body of scientists that periodically takes stock of global climate research and translates it into reports for governments worldwide. Three of the four were called “mitigation” pathways — futures where the world worked to reduce greenhouse gas emissions. One, the infamous and now obsolete RCP 8.5, was the “no-policy” baseline, a future with continued fossil fuel expansion, coal use roughly five times higher by 2100, and a global population pushing 12 billion. Think of it like Dickens’s Ghost of Christmas Future, a vision of just how bad things could get if we did nothing to change our ways.

And just like any dystopia, RCP 8.5 guaranteed attention. Between 2011 and 2020, more than 2,000 climate impact studies used RCP 8.5 as their default future. Almost every dramatic projection of crop failure, mass displacement, killing heat, and coastline retreat that any general reader ever encountered in climate change coverage depended on it.

All of those projections were plausible enough under the numbers set by RCP 8.5, but by the mid-2010s, researchers, journalists, and even official government reports were routinely calling the scenario “business as usual,” a phrase that transformed a stress test into something that sounded like a forecast. It wasn’t, and it was never meant to be. Somewhere along the way, though, that distinction got lost.

How the worst case got walked back

The world that RCP 8.5 assumed will never arrive. Global coal use isn’t on a path to quintuple; consumption has largely plateaued after decades of growth. Instead of the global population ballooning to 12 billion people, the UN’s current median forecast projects about 10.2 billion by 2100, with other reputable forecasts putting the number even lower. (All things being equal, fewer people means less emissions.)

At the same time, the clean energy transition moved faster than almost anyone in 2011 anticipated. The cost of solar power has fallen by about 85 percent since the RCPs were published, and annual global investment in the energy transition is now over $2 trillion. Actual global emissions have tracked far more closely to what you’d expect from a world trying to reduce them than from one doing nothing at all. By 2026, Climate Action Tracker estimated that current policies put the world on course for about 2.6 degrees of warming by 2100 — still serious, but a long way from 4 or 5.

Was RCP 8.5 ever realistic? One camp of experts, led by climate scientist Zeke Hausfather and energy modeler Glen Peters, argues that RCP 8.5 was plausible in 2011, but was taken off the table by genuine policy and technology progress. The other camp, led by Roger Pielke Jr., argues that the rate of global decarbonization has been roughly linear for decades. That would mean we didn’t actively avoid RCP 8.5; it was just never realistic to begin with. Both camps agree on what counts, though: RCP 8.5 should be gone, and the planet is still on track to warm between 2.5° and 3° by 2100.

RCP 8.5 was as much a climate journalism story as it was a climate science one. In 2017, the writer David Wallace-Wells published “The Uninhabitable Earth” in New York magazine. It was probably the most widely read piece of climate journalism of the last decade, and it was built almost entirely on RCP 8.5 projections.

Wallace-Wells revised his view in 2022, though there has been relatively little coverage of this year’s retirement of RCP 8.5. And researchers need to catch up: Pielke Jr. estimated that as late as early 2026, 30 new RCP 8.5 studies were coming out each day on average, generating more grist for the climate ultra-doom narrative. We’ll see whether last month’s announcement finally puts it to rest.

The future is in our hands

But even if we’ve averted doom, there is a lot of work to do to secure a safer future.

The new “medium” climate pathway — the one that reflects current policies — estimates 2.8°C of warming on average by 2100, with the likely range running from 2.1°C to 3.7°C. That would still mean drastic declines in coral reefs and accelerated species extinction, worsening water scarcity, and further sea level rise. And while we’ve taken the worst of the worst-case scenarios off the table, we’ve run out of time to keep warming below 1.5°C, and 2°C — the upper limit that the 2015 Paris Accords sought to prevent.

And as with anything to do with climate change, this scientific shift was quickly politicized. The day before Hausfather and his co-authors published their analysis of RCP 8.5’s retirement, President Donald Trump posted on Truth Social: “GOOD RIDDANCE!”, and described the change as proof that climate science was “WRONG! WRONG! WRONG!.” Not surprisingly, Trump is the one who is wrong here, as Carbon Brief explained in detail, but his mistake shows how easy it is to take the wrong lesson from the end of RCP 8.5. We shouldn’t fall for it.

The entire point of climate scenarios like RCP 8.5 was that there was no one certain future for climate change — only multiple possible futures. Whether or not RCP 8.5 was ever possible, the enormous advances in clean energy over the past 15 years are what made its retirement certain. Now we have new futures before us, waiting for what we do next.

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