In order to cool the planet significantly we would have to reduce carbon emissions to practically nothing, and then use carbon capture and storage to depress global CO2 from the current 404 ppm to about 320 ppm. If we could do that in time for the next Milankovitch glacial entry point (an orbital feature), then there is a reasonable chance than we could put Earth back into 'glacial mode'. But as time goes by, this gets less and less likely. By the time we double CO2 relative to the pre-industrial era, another glacial epoch looks highly unlikely. By the time we triple the CO2, we can kiss goodbye to glaciation for ever.