its a bit like the frog in the pot of water gradually being heated. It doesn't realise till its too late.
now did I get that story right?
That's if the water is getting hot then cold on an irregular cycle that gradually leads to increasing mean temps. The frog only notices the extremes and dies like an old pensioner who can't get to the mall to cool off. In that scenario one would count the numbers of dead frogs from year to year as a proxy just like we count dead pensioners.