To add to this, there are also feedback loops involved. Sea ice is very white (high albedo), and as it melts at the margins it is replaced by sea water with a m

To add to this, there are also feedback loops involved. Sea ice is very white (high albedo), and as it melts at the margins it is replaced by sea water with a much lower albedo that absorbs more light and heat energy. So as the ice goes, the water around it warms ever faster. Once the ice is mostly gone, that will accelerate global warming by an appreciable amount simply through loss of reflectivity. That's just one of many feedback loops that make things more complicated than "move the CO2 thermostat up or down again".