When it comes to how much our planet is warming, what counts is the cumulative emissions that we’ve pumped into the atmosphere. This is a matter of physics, not politics. In its 5th Assessment Report, the IPCC provided global carbon budgets—or the amount of carbon we could emit—and still hold global warming to certain temperatures. To have a 66% chance for staying below 1.5°C, we have now only some 200 gigatonnes of emissions left. If we accept a 50% chance, we have 350 gigatonnes.
Five years of current global annual emissions (38 gigatonnes of CO2 per year) would entirely consume the remaining carbon budget for a 66% chance of staying below 1.5°C . Accepting the higher budget for a 50% chance would give us 9 years.
To avoid blowing the 1.5°C carbon budget and give ourselves a chance for reaching the goals of the Paris Agreement, annual emissions need to go down steeply before 2020.