In the summer of 1783, the largest volcanic eruption of the past1,000 years killed 9,000 Icelanders, dumped three cubic miles of lavainto the surrounding region, and spewed out more than 100 million tonsof gases.

As if that weren’t bad enough, Rutgers University climatologist Luke Oman says, the eruption of the Laki volcano created a climatic disasterthat rippled all across the Northern Hemisphere and caused a faminethat cut the population of the Nile River valley by a sixth.

Using a NASA computer model, Oman tracked the worldwide effects ofthe sulfate aerosol cloud that formed following the Laki eruption. Theresults show that the cloud blocked enough sunlight to cool largeportions of Asia and North America. Tree ring data support the model’sconclusion, showing that in some areas, the summer of 1783 was thecoldest in more than 500 years. That chilling, in turn, disrupted thedelivery of seasonal rains to Africa and India. Because monsoons resultfrom the temperature differences between land and sea, the yearlymonsoon was so weakened that northern Africa and India experienced adevastating drought.

According to French scholar Constantin Volney, aclose friend of Benjamin Franklin’s who was traveling through Egypt atthe time, the land “could not be sown for want of being watered.” Theensuing famine cleared the once-busy streets of Cairo, where “all hadperished or deserted the city,” he wrote. Oman’s research is turning upother evidence of Laki’s far-flung influence. “Now we’re hearing aboutother places,” he says. “India had their own famine, and in Japan, itwas devastating for the rice crops; up to a million people died, sowe’re seeing many famines around the world. To see how this one eventcould cascade and impact so many areas was really amazing.”