It doesn't have to be large if you throw enough CO2 and other greenhouse gasses into the lower atmosphere, it just has to correlate. Far more concerning is the

It doesn't have to be large if you throw enough CO2 and other greenhouse gasses into the lower atmosphere, it just has to correlate. Far more concerning is the rate of change, which is unprecedented. There could be unforeseen impacts from the speed, and a new equilibrium from the already achieved temperature increase could be hundreds of years away as billions of cubic kilometres of ice takes a while to melt. 2C by 2100 is a reporting convenience. Ozone depletion measured CFCs in parts per trillion (US short scale).