Not all volcanoes of a given Index have the same effect; those closest to the equator make the most difference to global temperatures, hence the inclusion of latitude in the above table. Figure 1
demonstrates the effects of volcanoes on observed temperatures and temperatures calculated by global climate models. The observed data is based on the HadCRUTv3 data set and the modelled data are based on the average 7 models we present elsewhere (http://www.climatedata.info/temperature/model-simulations/index.html
). The data in the graph were calculated as the difference between the temperature in a particular year compared with the average temperature for the 5 preceding years.