The ship has largely sailed on limiting warming to 1.5C at this point, barring us getting very lucky with low climate sensitivity or actively geoengineering the climate. But there still are viable paths to limit warming to below 2C this century, as shown in the figure below:
If we want to meet our climate targets, we'd need to decrease global CO2 emissions from current levels to zero by: 1.5C with a 66% chance – 2030 1.5C with a 50% chance – 2035 2C with a 66% chance – 2069 2C with a 50% chance – 2079
@hausfath James Hansen-"Of course, one can devise a scenario that stays under 2°C via a miraculous transition to zero emissions within a few decades, but the real world pays no attention to imaginary scenarios. Instead, the real world responds to the actual growth of GHG climate forcings.”
@hausfath If Hansen is right & ECS is 4.8ºC & aerosol cooling is higher than IPCC assumes, then the chance of limiting temp to 2ºC is zero because we are already there (without aerosols). We *will* need geoengineering to stay under 2ºC.
@hausfath Do the scenarios you present assume large-scale negative emissions in the future?
@hausfath Taking CO2 out of the atmosphere (CDR) after a short overshoot (exceedance) is not the same as geoengineering the climate. We still have more options - but we must act fast and even faster.