Optimum for the organisms living these days.
What evidence do you have for that?
Evolution lags by about a million years, climate changes in a few millennia. Humans migrated out of Africa, to the colder climes of Europe and survived by wearing animal hides.
L
Just review the last several hundred years of history.
When it warmed man flourished and food was plentiful.
When it cooled man lived shorter and food was scarce.
Look up the climate in the dark ages. It was bitterly cold.
The black plague was likely caused by cooling:
http://earthsciencesus.blogspot.com/2008/01/black-death-and-climate-change.html
Throughout known history there is a consistent pattern.
“Optimum for the organisms living these days.”
I don’t know about you, but this “organism” is looking forward to a bit of Global Warming (Spring & Summer). I don’t like getting cold while working outside on projects too big to fit into the workshop!