How quickly would we need to reduce emissions to keep the global temperature rise below 1.5°C

Had we started reducing CO₂ emissions in 2000, the reductions target would have been 29.38b tonnes before the start of next century.
Starting in 2021, the reductions target would be 42.23b tonnes by 2083. With the same reduction target, but starting in 2026, we would only have a decade to achieve it before the temperature rise would hit 1.5°C.