https://en.wikipedia.org/wiki/Year_Without_a_Summer
Scientists later determined that the 1816 temperature anomaly was caused by volcanic eruptions in 1815 and 1814, which sprayed volcanic ash and sulfuric acid into the atmosphere, thereby shading the oceans and preventing them from storing the usual amount of heat over those two years.
Our modern Civilization is more vulnerable to an average once-a-millenium volcanic eruption than it's ever been, on account of our numbers and our dependency on supply chains for our sustenance.
From the linked article: "In fact, the U.N. Food and Agriculture Organization estimated the 2012 worldwide food storage to last for 74 days." (pg. 9)
Grains are useful because they store well. Storage is not economical, but it is essential for reducing the suffering which would result from an 1816-like scenario in our modern world.
Edit: the 1816 anomaly is classified as a volcanic winter [1]. Solar minimums have also resulted in years/decades with cooler summers than normal.