An interesting impact of an immediate stop of fossil fuel emissions is a rapid temperature increase over a few years due to an unmasking impact. i.e. the aerosols that are continually being produced due to fossil fuel burning drop out within days, weeks, months, increasing the solar radiation reaching the surface [0,1].

[0] https://www.nature.com/articles/s41558-022-01372-y (paywall)

[1] https://eprints.whiterose.ac.uk/188408/6/Dvorak_Armouretal_r... (pdf pre-print)