evidence: More significant are "grand solar minima," decades-long periods of reduced solar activity that have occurred 25 times in the last 11,000 years. A recent example, the Maunder minimum, which occurred between 1645 and 1715, saw solar energy drop by 0.04% to 0.08% below the modern average. Scientists long thought the Maunder minimum might have caused the "Little Ice Age," a cool period from the 15th to the 19th century; they’ve since shown it was too small and occurred at the wrong time to explain the cooling, which probably had more to do with volcanic activity. [...] During the Pleistocene epoch, which ended about 11,700 years ago, Milankovitch cycles sent the planet in and out of ice ages. When Earth’s orbit made northern summers warmer than average, vast ice sheets across North America, Europe and Asia melted; when the orbit cooled northern summers, those ice sheets grew again. Since warmer oceans dissolve less carbon dioxide, atmospheric carbon dioxide levels rose and fell in concert with these orbital wobbles, amplifying their effects. Today Earth is approaching another minimum of northern sunlight, so without human carbon dioxide emissions we would be heading into another ice age within the next 1,500 years or so.