One of the more terrifying elements of climate change is the uncertainty of it all. You start with the big picture of a warming planet, but as you zoom in you find ever more climatic and geological and biological systems interacting with one another—a complexity unfathomable for the human mind. We’re talking about a crisis that is affecting every organism and every square inch of this planet.
That makes calculating the carbon budget—the amount of greenhouse gases humanity can emit globally while adhering to certain goals—an unenviable task. (The goal of the Paris Agreement was 1.5 degrees Celsius above preindustrial levels; we’re already at 1 degree.) Different teams of researchers have reached wildly diverging conclusions, from “We can emit 1,000 gigatonnes more CO2 before we reach 1.5 degrees” to “Sorry, but we’ve already spent our carbon budget for 1.5.” There is simply too much uncertainty in the models.