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(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.

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I think this is negligible.

Space shuttle uses 0.6 million kilograms of liquid oxygen and 0.1 million kilograms of liquid hydrogen per each trip. So it's not even using fuels that would emit carbon. However, other launch vehicles could use carbon-based fuels.

Hydrogen has energy of 120 MJ/kg. Methane has energy of 50 MJ/kg. So if we replaced the hydrogen with methane, we would need 0.24 million kilograms of it. That would create 0.66 million kilograms of carbon dioxide per launch.

If we estimate there are 100 space launches per year, that would be 66 million kilograms of carbon dioxide per year. That's 66 kilotonnes.

Total CO2-equivalent emissions are 40 GtCO2/a. So about 0.000165% of emissions are due to space launches.

Even if a space launch would have major effects in some other way, such as by emitting black carbon, I'd say it's still negligible.

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    You say "it's not even using fuels that would emit carbon", but what about the processes to produce these fuels? Hydrogen can be made from renewable energy, but according to this article today, about 95% of all hydrogen is produced from steam reforming of natural gas.
    – THelper
    Jul 18 at 7:02
  • Well I did calculate numbers for using methane, the source of most hydrogen today. It shouldn't matter much whether the methane is first converted to hydrogen before burning, or burned directly.
    – juhist
    Jul 18 at 18:02

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