That's not entirely accurate. Short lived climate pollutants (SLCPs) that are being continuously emitted (e.g. SO4, NOx, contrail-cirrus) have cumulative effects. The heat trapped on earth is cumulative with a long equilibration time constant, and SO4 (not just from ships) has wiped out a huge fraction of the warming up to now.
(disclaimer that I manage a climate research group)
That's not entirely accurate. Short lived climate pollutants (SLCPs) that are being continuously emitted (e.g. SO4, NOx, contrail-cirrus) have cumulative effects. The heat trapped on earth is cumulative with a long equilibration time constant, and SO4 (not just from ships) has wiped out a huge fraction of the warming up to now.
(disclaimer that I manage a climate research group)