Soon after the Paris agreement was signed in 2015, and all countries agree to keep the levels of global warming below the 1.5C compared to pre-industrial levels, something odd started to transpire.

Nearly all modeled pathways for limiting global heating to 1.5°C above pre-industrial levels involved temporarily transgressing this target. Each still arrived back at 1.5°C eventually (the deadline being the random end point of 2100), but not before first shooting past it.

Scientists responsible for modeling the response of Earth's climate to greenhouse gas emissions—primarily caused by burning fossil fuels—called these "overshoot" scenarios. They became the dominant path along which mitigating climate change was imagined to proceed, almost as soon as talk of temperature limits emerged.

De facto, what they said was this: staying below a temperature limit is the same as first crossing it and then, a few decades hence, using methods of removing carbon from the atmosphere to dial temperatures back down again.

From some corners of the scientific literature came the assertion that this was nothing more than fantasy. A [new study published in Nature](https://www.nature.com/articles/s41586-024-08020-9) has now confirmed this critique. It found that humanity's ability to restore Earth's temperature below 1.5°C of warming, after overshooting it, cannot be guaranteed. Many impacts of climate change are essentially irreversible. Feedback loops triggered once warming passes a critical threshold (like those due to the loss of albedo caused by the melting of polar ice and the release of ancient methane stored for millennia under the permafrost) might take decades, or even centuries, to undo, well beyond the relevant horizon for climate politics. For policy makers of the future, it matters little that temperatures might eventually fall back again; the impacts they will need to plan for are those of the overshoot period itself.

https://phys.org/news/2024-10-mainstream-climate-science-endorsed-fantasy.html