It’s been a terrible year for tornadoes. An outbreak on April 27th created 305 tornadoes in the Deep South that killed 326 people. That was the worst one-day death toll from tornadoes since 1973. The disaster in Joplin, Missouri, on Sunday has killed at least 117, the worst death toll from a single twister since 1947.  The total of tornado deaths this year, 480 and sure to rise, is the worst since 1953. The New York Times has an animated chart detailing each year’s tornado numbers and deaths since 1950.

Climate change, inevitably, will be blamed for this year’s disasters because climate change is the currently fashionable explanation for “crazy weather.” In the 1950s the fashionable explanation for the equally crazy weather was atomic-bomb testing.

But if you want to know what’s actually responsible, the answer is North America. It’s a tornado-generating machine. If you want a means for creating the maximum number of tornadoes, here’s what you do. You take a vast landmass that covers both temperate and arctic latitudes, with a huge ocean to the west. Along the entire west coast of that landmass you place a range of high mountains that trends NNW to SSE. East of the mountains place a large expanse of relatively flat land. Finally, to the south of the plains, place a warm, subtropical sea. Voilà, you will create a lot of tornadoes every spring as cold, dry air flows down the east side of the mountains and warm, moist air flows up from the subtropical sea.

The United States has more tornadoes than the rest of the planet put together. It’s not climate change or God’s wrath or atomic testing. It’s the intersection of meteorology and topography.