Question: What is agreed to have caused the Little Ice Age during the Middle Ages?
About the article "Astronomy", section "Solar astronomy".

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The famine occurred in a period known as the Little Ice Age.
During the 1690s, climate in Europe was characterised by cold springs and summers.
It is generally estimated that temperatures were 1.5oC lower during the 1690s than the average during the Little Ice Age.
This impacted other countries, France suffered the worst famine since the Middle Ages, ice floes formed in the Thames while Lake Constance and Lake Zurich froze completely over. 
Effect on humans.
Effects on populations.
Weather has played a large and sometimes direct part in human history.
Aside from climatic changes that have caused the gradual drift of populations (for example the desertification of the Middle East, and the formation of land bridges during glacial periods), extreme weather events have caused smaller scale population movements and intruded directly in historical events.
One such event is the saving of Japan from invasion by the Mongol fleet of Kublai Khan by the Kamikaze winds in 1281.
French claims to Florida came to an end in 1565 when a hurricane destroyed the French fleet, allowing Spain to conquer Fort Caroline.
More recently, Hurricane Katrina redistributed over one million people from the central Gulf coast elsewhere across the United States, becoming the largest diaspora in the history of the United States.
The Little Ice Age caused crop failures and famines in Europe.
The 1690s saw the worst famine in France since the Middle Ages.
Finland suffered a severe famine in 1696–1697, during which about one-third of the Finnish population died. 
There have been five known ice ages in the Earth's history; the Earth is experiencing the Quaternary Ice Age during the present time.
Tunnel valleys formed during four of the five have been identified.  
The Ice Age Centre is a museum dedicated to the understanding of ice ages, located in Äksi village, Estonia.
The museum strives to popularise knowledge about the origins and dynamics of different ice ages, including their effect on the landscape, animal life and humans, with a special focus on the impact of the latest ice age on what is today Estonia. 
Icecap climates have only existed in ice ages.
There have been at least five such ice ages in the Earth's past.
Outside these ages, the Earth seems to have been ice-free even in high latitudes.
By the geologic definition, Earth is currently in an ice age, in that the planet has permanent ice caps.
Factors that cause ice ages include changes to the atmosphere, the arrangement of continents, the energy received from the sun, volcanos, and meteor impacts.
The current era is believed to be the only time in the last 600 million years of Earth's history with ice caps at both poles.
The Antarctic ice cap was formed after Antarctica split from South America, allowing the formation of the Antarctic Circumpolar Current.
The Arctic ice cap was partially caused by the Azolla event, where a large number of ferns in the ocean died, sank, and never decayed, which trapped carbon dioxide beneath the ocean.
There is a hypothesis that around 650 million years ago, the entire planet was frozen, called Snowball Earth.
Essentially the entire planet had an ice cap climate.
However, this theory is disputed, and even proponents suggest there was an area of periodic melting near the equator.