Billions of dollars are spent every year to speculate on what the climate would be like below 350 ppm CO2. This is possibly the stupidest venture in scientific history, because we have huge amounts of historical information available about what the climate actually was like below 350ppm.
The primary purpose of climate models is to legitimize confirmation bias. Modelers will obtain whatever result they seek to obtain.
With four parameters I can fit an elephant, and with five I can make him wiggle his trunk.
John von Neumann