evidence that low solar activity may have contributed to the LIA through the increased occurrence of cold winters, at least in Europe, but colder summers are more correlated with volcanic activity. Numerical climate modelling indicates that volcanic activity was the greater driver of the overall lower temperatures in the little ice age, as seen in a variety of paleoclimate proxies. Volcanic activity In a 2012 paper, Miller et al. link the Little Ice Age to an "unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading >60 Tg" and notes that "large changes in solar irradiance are not required." Throughout the Little Ice Age, there was heightened volcanic activity. When a volcano erupts, its ash reaches high into the atmosphere and can spread to cover the whole earth. The ash cloud blocks out some of the incoming solar radiation, which leads to worldwide cooling for up to two years after an eruption. Also emitted by eruptions is sulfur in the form of sulfur dioxide. When sulfur dioxide reaches the stratosphere, the gas turns into sulfuric acid particles, which reflect the sun's rays. That further reduces the amount of radiation reaching the Earth's surface. A recent study found that an especially severe tropical volcanic eruption in 1257, possibly Mount Samalas (pre-caldera edifice of the active Rinjani) near Mount Rinjani, both in Lombok, Indonesia, followed by three smaller eruptions in 1268, 1275, and 1284, did not allow the climate to recover. That may have caused the initial cooling, and the 1452/1453 mystery eruption triggered a second pulse of cooling. The cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed. Other volcanoes that erupted during the era and may have contributed to the cooling include Billy Mitchell (c. 1580), Huaynaputina (1600), Mount Parker (1641), Long Island (Papua New Guinea) (ca. 1660), and Laki (1783). The 1815 eruption of Tambora, also in Indonesia, blanketed the atmosphere with ash, and the following year came to be known as the Year Without a Summer, when frost and snow were reported in June and July in both New England and Northern Europe. Ocean circulation Around 2000s, the slowing of thermohaline circulation was proposed as an explanation. The circulation could have been interrupted by the introduction of a large amount of fresh water into the North Atlantic and might have been caused by a period of warming before the