Scientists estimate that there were four times the number of severe tornadoes in the U.S. as there are in any other continent. The main reason for this is the particular geography of North America. Uniquely, there is no major mountain chain that runs along the continent’s east-west axis, so no major topographical obstacles exist to block the flow of air from the north to the south. As a result, cool air currents from the north can clash directly with the warm and humid air from the south, which has picked up moisture from the Gulf of Mexico. This can lead to the creation of huge storms, known as supercells, which provide the strong and continuous updraft needed to spawn tornadoes. Based on the information in the paragraph, what can be deduced about continents other than North American?