In April 1815, Mount Tambora, on the Indonesian island of Sambawa, experienced a colossal eruption, with a rating of 7 on the Volcanic Explosivity Index (VEI). Tens of thousands of people died, about 100 cubic kilometers of rock blasted into the air, and the resulting sulfate aerosol in the upper atmosphere led to drastic weather changes in North America and Europe, causing food shortages. The following year, 1816, is known as the “Year without a Summer” due to the major climate abnormalities, and proved to be inspirational for art and literature (for example, Lord Byron, Mary Shelley, J.M.W. Turner).
A previous VEI 7 eruption in the region, of the Indonesian volcano Samalas at Mount Rinjani in 1257 CE was implicated in the onset of a centuries-long cold period between the 14th and the 19th century called the Little Ice Age.
Fortunately, the recurrence frequency of VEI 7 eruptions somewhere in the world is between one and two per thousand years, but this should not cause complacence in preparing for future events. Volcanologist Chris Newhall, with co-authors Stephen Self and Alan Robock, have recently published a paper in Geosphere exploring the potential consequences of the next VEI 7 eruption distinguishing between proximal and distal zones of hazards and risk. This study is not purely focused on catastrophic effects, but rather encourages other research groups to carry out studies and simulations in order to discuss the challenges for the short-range forecasting of such events and offer governments clear scientific bases on which to organize their prevention and emergency policies.
The forecasts of Newhall et al.  predict the drastic effects of a large volcanic event on a global scale in societies like ours that are increasingly connected, both in the fields of transport and data transmission. Our world is changing faster than at any time in human history and the next VEI 7 will strike a world very different from that affected by the last two eruptions.
For example, more than 100,000 commercial flights take place in the world every day, and vast volumes of data are transmitted via communication satellites. The failure of the satellite-based global positioning system (GPS), a fundamental resource for geographical positioning, would create unprecedented problems for transport systems. It would affect aircraft, cars and other means of transport, for people, animals and goods.
As a comparison, consider what happened during the 2010 eruption of the Icelandic volcano Eyjafjallajökull, although it was only VEI 3. A large column of smoke and dust reached the middle troposphere, spreading over part of Europe and the Atlantic Ocean by the winds. For safety reasons, a large number of scheduled flights were suspended, complicating the connections between Europe and North America, and beyond. The problem also involved the air transport of goods, leading to delays, errors, and estimated damages of over 4 billion euros.
The world population has grown from 1 billion in 1815 to over 7.6 billion in 2018, with an increasing number of people living close to volcanoes with a major eruption potential.
Newhall et al. have identified a list of candidate volcanoes that might be capable of a VEI 7 eruption. These include the Taupo Volcano in New Zealand, which produced an enormous VEI 8 eruption around 26,500 years ago, and the Campi Flegrei calderas along the Bay of Naples in Italy.