The connection of solar UV light and its variability to climate change is controversial among scientists. Recent measurements of the sun's total irradiance show that it varied by about 0.1% during the recent 11 year solar cycle. Computational models indicate that this level of variation is insufficient to significantly modulate the climate. However, the models do not include subtle feedback mechanisms (e.g. enhanced cloud formation) which could magnify the impact of this tiny variation. It is also possible that changes in the Earth's upper atmosphere induced by solar UV light could similarly affect the surface climate. Yet, skeptics point out that the energy per unit volume stored in the tropopause (the boundary between the troposphere and the stratosphere) is 100 times greater than in the upper atmosphere indicating that such causality is unlikely. Numerous correlations between solar activity and climatic events have been claimed in the past, many of which were abandoned when their statistical significance could not be convincingly established. A dramatic example of a connection which remains credible occurred during the extended seventeenth century period known as the Little Ice Age which was characterized by Earth surface temperatures much colder than normal and which coincided with a very unusual period of low solar activity and no sunspots known as the Maunder Minimum.