The impacts of pollution resulting from large explosive volcanic eruptions on the atmospheric heat budget and planetary albedo are not in doubt1,2. However, the effects of volcanic aerosols on the surface climate are less clear and still controversial3,4. In a previous study5 it was shown that significant surface cooling occurs over the landmasses of the Northern Hemisphere in the first few months after a major eruption in that hemisphere. Here we extend that work using new surface-air temperature compilations based on land and marine data6 for both the Northern and Southern Hemispheres. Our results indicate that major Northern Hemisphere eruptions have an immediate effect on the Northern Hemisphere average surface temperature but little or no effect on the Southern Hemisphere average. Southern Hemisphere eruptions affect both Southern and Northern Hemisphere temperatures after a lag of between six months and a year.