We are not on the best path. We are somewhere in the middle.
Durante décadas, os cientistas do clima construíram os seus modelos em torno de cenários que mapeavam futuros possíveis, incluindo o mais sombrio de todos — um mundo onde os combustíveis fósseis dominavam sem entraves e o planeta aquecia cerca de 4,5 graus Celsius até ao fim do século. Esse cenário extremo, conhecido como RCP8.5, foi agora retirado das projeções internacionais mais recentes, não porque o perigo climático tenha diminuído, mas porque a expansão das energias renováveis e a eletrificação tornaram esse futuro improvável. A decisão reflete uma mudança real no panorama tecnológico e económico, mas os especialistas alertam que o caminho em que o mundo se encontra continua a ser profundamente preocupante — longe do pior caso, mas também longe do melhor.
- O cenário RCP8.5, que projetava um aquecimento catastrófico de 4,5°C, foi eliminado dos novos modelos climáticos internacionais, gerando debate imediato entre cientistas e decisores políticos.
- Alguns governos e grupos de interesse apressaram-se a interpretar a remoção como uma boa notícia, sugerindo que a crise climática estaria a ser resolvida — uma leitura que os especialistas rejeitam com firmeza.
- A mudança reflete progressos reais nas renováveis e na eletrificação, mas não uma vitória climática: o mundo continua a emitir a um ritmo que torna o objetivo de 1,5°C cada vez mais difícil de alcançar.
- Os modelos climáticos continuarão a evoluir à medida que as economias, tecnologias e políticas energéticas se transformam, mantendo os cenários como ferramentas essenciais de avaliação de risco e planeamento de adaptação.
Durante décadas, os cientistas do clima organizaram as suas previsões em torno de cenários que descreviam futuros possíveis consoante as escolhas da humanidade. O mais extremo desses cenários chamava-se RCP8.5 — mais tarde atualizado para SSP5-8.5 — e assumia que os combustíveis fósseis continuariam a dominar a economia global sem qualquer restrição significativa, levando a um aumento de temperatura de cerca de 4,5 graus Celsius até ao final do século XXI. Era o pior caso que os modelos conseguiam imaginar, e durante anos foi o cenário que gerou as manchetes mais alarmantes.
Esse cenário foi agora retirado da nova geração de projeções climáticas internacionais. A razão não é que o clima esteja a melhorar, mas que o mundo mudou desde que o RCP8.5 foi concebido. As energias renováveis expandiram-se de forma dramática, os veículos elétricos tornaram-se cada vez mais comuns e a tecnologia de baterias avançou consideravelmente. O futuro que o cenário assumia — uma dependência crescente e irrestrita dos combustíveis fósseis — tornou-se simplesmente menos plausível, não por força de políticas climáticas deliberadas, mas porque a economia e a tecnologia seguiram outro rumo.
No entanto, os especialistas alertam contra qualquer leitura triunfalista desta decisão. O caminho mais favorável, aquele que limitaria o aquecimento a 1,5 graus Celsius, está a tornar-se cada vez mais difícil de alcançar. O mundo não está no pior cenário, mas também não está no melhor. Está algures no meio — e o meio continua a ser profundamente preocupante. Remover o caso extremo dos modelos não invalida os avisos anteriores nem reduz a urgência da ação climática; significa apenas que os cenários, como qualquer ferramenta científica, devem ser atualizados à medida que a realidade evolui. O trabalho de compreender o que está por vir, e de nos prepararmos para isso, continua.
For decades, climate scientists have built their forecasts around different possible futures—scenarios that map out how the planet might warm depending on the choices humanity makes. Some of these paths assume rapid cuts to emissions and a swift shift away from fossil fuels. Others paint a darker picture: a world where coal, oil, and gas remain the backbone of the global economy, emissions keep climbing, and no serious effort is made to slow them down. That darkest scenario had a name: RCP8.5, later updated to SSP5-8.5. It was the worst case the models could imagine.
For years, RCP8.5 appeared in the most alarming climate studies, the one that made headlines and shaped public fear. It assumed fossil fuel consumption would surge throughout the twenty-first century without meaningful restraint. Under those conditions, atmospheric carbon dioxide would reach unprecedented levels, and global temperatures could rise roughly 4.5 degrees Celsius above pre-industrial times by the century's end. It was a scenario built on the assumption that the world would essentially do nothing.
That scenario no longer appears in the newest generation of international climate projections. Scientists have removed it from the models they use to forecast the future. The decision has sparked intense debate, particularly among policymakers eager to interpret it as good news. But climate experts are pushing back hard against that reading. Removing the worst-case scenario, they insist, does not mean climate change is less dangerous, nor does it suggest that earlier warnings were wrong.
Why was the most extreme scenario dropped? The answer lies in how the world has actually changed since RCP8.5 was designed. When researchers first conceived the scenario, they thought it plausible that global economic growth would continue to depend overwhelmingly on fossil fuels. But the last two decades have rewritten that assumption. Renewable energy has expanded dramatically. Electric vehicles are becoming mainstream. Battery technology has improved. The technological and economic landscape looks different now than it did when the scenario was built. RCP8.5 assumed a future that is becoming harder to reach, not because of climate policy success, but because the underlying economics have shifted.
Yet removing the catastrophic scenario comes with a sobering caveat. The most favorable pathway—the one that would limit warming to 1.5 degrees Celsius—is not the one the world is actually on. New projections show that hitting that target is becoming increasingly difficult. The disappearance of the worst case can be read as a sign of progress, a signal that human action is working. But the real story is more complicated. We are not on the best path. We are somewhere in the middle, and the middle is still deeply concerning.
Climate scenarios work by combining data on population, economics, technology, energy use, and public policy to construct different possible futures. Research centers around the world then feed these scenarios into sophisticated climate models that simulate how the atmosphere, oceans, ice sheets, and ecosystems will respond. The result is not a single prediction but a range of outcomes, each one useful for assessing risk and designing adaptation strategies. Because the world keeps changing—economies shift, technologies emerge, energy policies evolve—the scenarios themselves must be updated. RCP8.5 was not wrong when it was created. It simply no longer represents a plausible future. But that does not mean the remaining scenarios are reassuring. The work of understanding what comes next, and preparing for it, continues.
Citações Notáveis
Removing the worst-case scenario does not mean climate change is less dangerous, nor does it suggest that earlier warnings were wrong— Climate scientists
A Conversa do Hearth Outra perspectiva sobre a história
So scientists are saying the worst-case scenario won't happen. That sounds like progress.
It does sound that way, but it's more subtle than that. They're not saying the climate won't warm dangerously. They're saying the specific path that led to 4.5 degrees of warming is now implausible because renewable energy and electric vehicles have become real in ways nobody fully expected.
But if that scenario is off the table, doesn't that mean we're doing better than we thought?
Not exactly. It means the economic assumptions underlying that scenario have changed. We're not on the best path—the 1.5-degree path. We're somewhere in the middle, and the middle is still very bad.
What does that mean in practical terms?
It means we've made some progress on technology, but we haven't made the policy choices needed to actually use that technology at scale. The scenarios that remain on the table all show significant warming and serious impacts.
So removing RCP8.5 is just housekeeping?
It's more like updating your map when the terrain changes. The map was accurate when it was drawn. But the world has moved, and the scientists are adjusting their tools to reflect reality. That's responsible. But it doesn't mean the danger has passed.