I have started reading a booked called, The Planet Remade by Oliver Morton, which is about geo-engineering. I have just read the chapter about volcano emissions (e.g. Pinatubo, Krakatau, Tambora) caused a bit of a cool down. Several interesting this happened: sulphur dioxide was shot into the stratosphere were it combined with water vapour to produce an aerosol of sulphuric acid droplets; the sulphuric acid droplets spread to cover a fair percentage of the earth reflected a percentage of light back into space; the sulphuric acid droplets diffused direct sunlight before it hit the earth; plant life grew more rapidly drawing down more CO2 because plants prefer diffuse light to direct sunlight; the rate at which fungi broke down dead plants, releasing CO2, slowed down because the planet was cooler. That was interesting. I was aware of the reflecting light back into space effect, but not the others.