There are shorter climate periods that could be said roughly to account for large scale climate trends in the Post-classical Period. These include the Late Antique Little Ice Age, the Medieval Warm Period and the Little Ice Age. The extreme weather events of 536–537 were likely initiated by the eruption of the Lake llopango caldera in El Salvador. Sulfate emitted into the air initiated global cooling, migrations and crop failures worldwide, possibly intensifying an already cooler time period. Records show that the world's average temperature remained colder for at least a century afterwards.