onset of the Little Ice Age also occurred well before the beginning of the Maunder Minimum, and northern-hemisphere temperatures during the Maunder Minimum were not significantly different from the previous 80 years, suggesting a decline in solar activity was not the main causal driver of the Little Ice Age. The correlation between low sunspot activity and cold winters in England has been analyzed using the longest existing surface temperature record, the Central England Temperature record. A potential explanation of this has been offered by observations by NASA's Solar Radiation and Climate Experiment, which suggest that solar ultraviolet light output is more variable over the course of the solar cycle than scientists had previously thought. A 2011 study found that low solar activity was linked to jet stream behavior, resulting in mild winters in some places (southern Europe and Canada/Greenland) and colder winters in others (northern Europe and the United States). In Europe, examples of very cold winters are 1683–84, 1694–95, and the winter of 1708–09. Other observations Past solar activity may be recorded by various proxies, including carbon-14 and beryllium-10. These indicate lower solar activity during the Maunder Minimum. The scale of changes resulting in the production of carbon-14 in one cycle is small (about one percent of medium abundance) and can be taken into account when radiocarbon dating is used to determine the age of archaeological artifacts. The interpretation of the beryllium-10 and carbon-14 cosmogenic isotope abundance records stored in terrestrial reservoirs such as ice sheets and tree rings has been greatly aided by reconstructions of solar and heliospheric magnetic fields based on historic data on Geomagnetic storm activity, which bridge the time gap between the end of the usable cosmogenic isotope data and the start of modern spacecraft data. Other historical sunspot minima have been detected either directly or by the analysis of the cosmogenic isotopes; these include the Spörer Minimum (1450–1540), and less markedly the Dalton Minimum (1790–1820). In a 2012 study, sunspot minima have been detected by analysis of carbon-14 in lake sediments. In total, there seem to have been 18 periods of sunspot minima in the last 8,000 years, and studies indicate that the Sun currently spends up to a quarter of its time in these minima. A paper based on an analysis of a drawing by John Flamsteed suggests that the Sun's surface rotation slowed in the deep Maunder Minimum (1684). During the Maunder