believe that dust and sulphate aerosols, usually concomitant to volcanic eruption, mainly affect the quantity and quality of solar radiation that reaches the earth. The dust scatters and partially reflects incoming solar radiation whereas the aerosols act as cloud-condensation nuclei. Both cause reduced temperatures for short-lived periods unless the volcanic eruptions are very large. Tree ring evidence has found that cool summers since the 17th century have indeed been primarily due to volcanic eruptions. Volcanic eruptions can further influence climate by their pollution of the oceans. some of the dust will settle into the water body, providing nutrients such as iron and other cations, which may stimulate primary productivity in maine phytoplankton. Their uptake of carbon dioxide could reduce its concentration in the atmosphere and contribute to global cooling by diminishing the greenhouse effect. There can be little doubt that the combination of these, and various other factors, does induce a varying degree of cyclical climatic change. However, some suggest that none of them contribute sufficiently to create positive feedback that would effect changes in the magnitude of glacial-interglacial swing. It is now widely accepted that astronomical forcing, the Milankovitch theory, is the most important primary cause of Quaternary glacial-interglacial cycles and probably those of earlier geological periods....It is the change in the orbital eccentricity that is thought to drive the glacial interglacial cycle. These cycles influence the amount of solar radiation received at the Earths surface, especially in the high latitudes of the northern hemisphere. However, these cycles have proven to have little effect on insulation. Other non-naturally occurring factors are therefore responsible for the climatic changes anticipated. Popular causes are the greenhouse gases, notably carbon dioxide and methane, whose changes in atmospheric c...
