After a large volcanic eruption, the layer of sulfate
aerosols in the stratosphere gets thicker, and we see, in the historic record, that the Earth cools down in response.
Rough calculations show if you drill about a dozen mine shafts as deep as possible into the thing, and plunk megaton nuclear bombs down there, and then fire them off simultaneously, you'll
get a repeat of the Long Valley Caldera explosion of about 800,000 years ago — which coated everything east of it with miles of ash and injected a giant
aerosol cloud into the
stratosphere — the ash layer alone formed a triangle stretching from the caldera to Louisiana to North Dakota, including all of Arizona and most of Idaho and everything
in between — I bet that would have a cooling factor of at least -30 W / m ^ 2 — and you could go and do the Yellowstone Plateau at the same time — geoengineering at its finest.
«This doesn't necessarily mean that every eruption will be able to
get sulfur dioxide into the
stratosphere and form
aerosols, but they are just neglected entirely
in the climate models from the [Intergovernmental Panel on Climate Change],» Ridley said.