Climate Risk Is Not a Single Number: Why Emissions Uncertainty Matters

Climate scientist Zeke Hausfather argues that treating climate outcomes as a single central estimate, like 2.9C by 2100 under current policies, hides the real risk of much higher warming. Carbon cycle feedbacks and climate sensitivity create wide uncertainty, meaning we could end up at 4C or even 5C if the climate system responds strongly to emissions. The piece notes that land areas have already warmed past 2C, and regional changes are often larger than global averages. It also warns that policy reversal, such as subsidizing fossil fuels, could push us into the high emissions scenario with a 70% chance of exceeding 4C by 2150. The takeaway: progress in bending the emissions curve is real, but the remaining risk is too high to justify complacency.