In maths I learnt that an asymptote is a line which gets closer and closer to another line but never actually reaches it.
This is happening with climate change science.
The fourth assessment report by the Intergovernmental Panel on Climate Change found “unequivocal evidence” of warming, with a 90% chance of humans being the cause. The draft fifth IPCC assessment talks of near certainty, with a 95% change of humans being the cause.
How close can you go without being certain?
Perhaps the sixth assessment will be “for all intents and purposes certain” (98%), the seventh will be “all but certain” (99%), the eighth will refer to “tiny residual doubt” (99.5%). As the decades pass we will struggle for phrases which steadily get closer to certainty without actually expressing certainty.
Thus scientists will never put it on a plate for politicians. There is always a gap, a thread of uncertainty where political leadership and courage will be required.