The “carbon budget” is an estimate of how much CO₂ we can still emit, but still have a good chance to keep global warming from going over the 1.5°C limit into “dangerous” territory. The budget has recently been revised (upward, thank goodness) to about 420 GtCO₂ (420 billion tons of carbon dioxide).

Staying within the 1.5°C limit doesn’t make us “safe” — there are still consequences of climate change, dangerous and costly, and we’re already paying the price despite not having hit 1.5°C yet. But going above 1.5°C takes us into what is best described as: nobody wants to go there.