A huge amount of $\small\mathsf{CO_2}$ is absorbed by the ocean and stored in the ocean, and methane is stored as clathrates. For every mega-meteorite or asteroid that impacts on land, two hit the sea. In a range of sizes between Barringer and Chicxulub, how big would a mega-meteorite have to be to release climate changing amounts of $\small\mathsf{CO_2}$ and methane from the sea? The multi-megaton fusion device that destroyed Elugulab Island in the Eniwetok atoll, Marshal Islands, in 1952 was considerably more powerful than the Barringer meteorite, but does not appear to have released significant amounts of greenhouse gases. Obviously a lot depends on where in the ocean the mega-meteorite lands, so let's say it lands in a place with higher than average quantities of $\small\mathsf{CO_2}$ and methane.

  • $\begingroup$ There is thought to be climate changing amounts of CO2 from Chicxulub hitting carbonate rocks. I haven't done the math, but I don't think there would be that much clathrates and dissolved CO2 in the impact area. $\endgroup$ Nov 8, 2019 at 3:32
  • $\begingroup$ @Keith McClary: Oceans are also fairly thin, compared to the depth of the crater created by a Chicxulub-sized impact. The area in which CO2 & clathrates would be released would be the size of the crater or less, probably not enough for major effects. But sulfate rocks are apparently a different story: en.wikipedia.org/wiki/Chicxulub_crater#Effects $\endgroup$
    – jamesqf
    Nov 8, 2019 at 3:46
  • $\begingroup$ It's an interesting notion, but why do you think that meteorites would possess significant amounts of GHG? Dominant gas species under space conditions with a solar elemental mixutre are $\rm CO$ and $\rm H_2 O$, so are you alluring towards water here? $\endgroup$ Nov 8, 2019 at 12:41
  • $\begingroup$ It's the ocean which possesses the greenhouse gases. $\endgroup$ Nov 8, 2019 at 13:08
  • 2
    $\begingroup$ Well, then the released amount of $CO_2$ will be proportional to the evaporated amount of water, which again is a fraction of the kinetic energy of the impactor. Note that released $CO_2$ will be absorbed by the ocean again at cooled post-impact conditions. $\endgroup$ Nov 8, 2019 at 17:02


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