section_path: Global trends/Climate
section_name: Climate
paragraph_text: Climate
  
  During post-classical times, there is evidence that many regions of the world were affected similarly by global climate conditions; however, direct effects in temperature and precipitation varied by region. According to the Intergovernmental Panel on Climate Change, changes did not all occur at once. Generally however, studies found that temperatures were relatively warmer in the 11th century, but colder by the early 17th century. The degree of climate change which occurred in all regions across the world is uncertain, as is whether such changes were all part of a global trend. Climate trends appear to be more recognizable in the Northern than in the Southern Hemisphere however, there are instances where climate in areas without written records have been estimated, historians now believe the Southern Hemisphere became colder between 950 and 1250.
  
  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 Ilopango 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.
  
  The Medieval Warm Period from 950 to 1250 occurred mostly in the Northern Hemisphere, causing warmer summers in many areas; the high temperatures would only be surpassed by the global warming of the 20th/21st centuries. It has been hypothesized that the warmer temperatures allowed the Norse to colonize Greenland, due to ice-free waters. Outside of Europe there is evidence of warming conditions, including higher temperatures in China and major North American droughts which adversely affected numerous cultures.
  
  After 1250, glaciers began to expand in Greenland, affecting its thermohaline circulation, and cooling the entire North Atlantic. In the 14th century, the growing season in Europe became unreliable; meanwhile in China the cultivation of oranges was driven southward by colder temperatures. Especially in Europe, the Little Ice Age had great cultural ramifications. It persisted until the Industrial Revolution, long after the post-classical period. Its causes are unclear: possible explanations include sunspots, orbital cycles of the Earth, volcanic activity, ocean circulation, and man-made population decline.