Global warming is our current focus, but from 1810 to 1819, people worried because the planet was far colder than usual, with the planet cooling almost a full degree Fahrenheit. 1816 according to climate historians was known as "the year without a summer."
The chill of 1816 has long been blamed on an Indonesian volcano called Tambora, which erupted the year before. But why the years before Tambora's eruption were also colder than usual was a mystery. Recently uncovered evidence in the ice of Antarctica and Greenland suggests that another volcanic eruption may have contributed to the worldwide dip in temperatures.
Jihong Cole-Dai, a chemistry professor at South Dakota State University, led the expeditions to Antarctica and Greenland, told NPR's Guy Raz in an interview that volcanoes dump large quantities of ash and sulfur dioxide into the atmosphere, which acts "like a giant window shade, reflecting sunlight and lowering temperatures on the ground for years afterward."
But Cole-Dai empasizes that one eruption isn't enough to freeze an entire decade. He knew something else had to have been going on which turned out to be layers of sulfur buried in ice cores from Greenland and Antarctica that showed another volcano had erupted some time in 1809, triggering a mini ice age.
Cole-Dai said his research team isn't sure exactly where the mystery volcano is, but they suspect that it was somewhere near the equator and that it had to be large enough to blanket the planet in ash.