How many global warming equivalents does a volcano spew out?

Apparently it depends on the volcano. Realclimate has some good discussions of it. The closer to the tropics and the larger the amount of S02, the more significant the cooling. The farther away and the more ash instead of S02, the less. I think the last noticeable one was Pinatubo, and that only shows as a blip on the line. Reading some comments on realclimate, at this stage nobody thinks this one will have much impact. Let me see if I can get a graph with Pinatubo labeled.

Here's a brief general discussion:

RealClimate

Can't seem to find a graph handy, sorry. Several sources say the aerosols from Pinatubo were essentially gone in three years. Cooling was cited at about half a degree centigrade. But short lived. Obviously, if you got a bigger volcano, it would have more impact.

 

There you go. Just as chogan2 describes.

 

A 'nonstandard' view of lighning production by volcanic erutions:

Volcanic Lightning

The CO2 associated with volcanic eruptions is the 'warming agent'. Suspended ash has an opposing effect, but does not persist for long in the troposphere. Really powerful erupttions can inject ash (and, importantly, SO2) into the stratosphere. Those can cool the earth for 1 to a few years.

edit: If not clear fromAlric's figure, the Pinatubo eruption of interest was 1991. El Chinchon was 1982. Both 'did' the stratosphere, but Mt. St. Helens did not. That one sort of squirted sideways.

 

A 27 MT squirt!

 

Sure it was big Tripp, but not a stratosphere punch. Instead the ash killed a lot of car engines. Y'all know to not drive through volcanic ash, right? Pointy little particles...

 

True...true. But you're the one who said it "squirted". I just put a magnitude on the squirting.