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What possible causes of the Little Ice Age do climatologists study?

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Line graph showing estimated temperature variations from 1000 to 2000 CE for the Northern Hemisphere and central England, with three lines representing different data sources. The chart highlights the medieval warm period around 1100-1300 and the Little Ice Age from about 1500 to 1850, followed by a sharp temperature rise in the late 20th century. Temperature is shown as deviations from the 1961-1990 average. — Little Ice Age Estimates of temperature variations for the Northern Hemisphere and central England from 1000 to 2000 ce.

While the exact cause of the Little Ice Age remains uncertain, climatologists study three primary factors that may have contributed to the onset and extension of this climate interval:

Variability in solar output: Scientists have observed that the coldest years of the Little Ice Age in parts of Europe coincided with periods of unusually low sunspot activity, specifically the Spörer Minimum (1450–1540) and the Maunder Minimum (1645–1715). This suggests that reduced solar radiation may have played a role, though it does not fully explain cooling episodes in all regions of the world.12
Changes in large-scale atmospheric patterns: Many researchers point to a reversal of the North Atlantic Oscillation (NAO). A shift to a "negative" phase would have funneled moisture toward the Mediterranean and allowed cold Arctic air to move over northern Europe, potentially driving regional climate variability.1
Increased volcanism: Explosive volcanism can propel gases and ash into the stratosphere, reflecting solar radiation and lowering global temperatures. Some scientists hypothesize that such activity may have strengthened the negative phase of the NAO, further cooling northern Europe.1