"The popular idea of cutting our emissions in half in 10 years only gives us a 50% chance of staying below 1.5C degrees, and the risk of setting off irreversibl

"The popular idea of cutting our emissions in half in 10 years only gives us a 50% chance of staying below 1.5C degrees, and the risk of setting off irreversible chain reactions beyond human control." Where does this 50% come from? Is this number realistic?