(I haven't received a proper answer on Earth Science SE so I decided to try my luck here since I can't yet start a bounty)
Do space launches warm or cool the surface temperature (admittedly, for a little bit)? This BBC article presents it as an emerging climate problem but also says
If the amount of black carbon expelled into the atmosphere reach 30 gigagrams a year, or even 100, then there will be some cooling of the surface of the planet under this black carbon umbrella.
So what's the whole debate all about then? Isn't it a good thing that it counteracts the warming effect to some degree?
UPD: I've found an answer
The 2010 global climate model study considered rocket BC emissions of 600 tons per year, more than double the current BC emissions of about 225 tons. Run for 40 model years to ensure the model reached steady state, the stratospheric BC burden grew to 2,400 tons. Although the globally averaged surface temperature anomaly was small and not statistically significant, on smaller scales and over limited latitude bands, significant positive and negative temperature anomalies emerged. North polar surface temperatures increased by more than 1°C, and upward of 5% of polar sea ice coverage was lost. And beneath the main BC accumulation in the northern midlatitudes (around the latitude of the assumed launch site at 33°N), the surface cooled by 0.5°C.