© Associated PressThe tornado that tore through Joplin, Missouri, leaving scores dead.
A tornado is a rotating column of air that stretches from the bottom of clouds to the Earth's surface. They can occur in a wide range of shapes and sizes, typically manifesting as a funnel of condensation surrounded by a cloud of dust and debris. Wind speeds in an average tornado reach more than 100mph (160km/h) and the system itself is less than 100 metres across, but extreme events can be several miles across, with wind speeds of more than 300mph.
It is difficult to relate any individual weather event to climate change and, unlike with hurricanes, there is little robust research on whether the warming planet is causing any noticeable effects. Grady Dixon, assistant professor of meteorology and climatology at Mississippi State University, told AFP: "If you look at the past 60 years of data, the number of tornadoes is increasing significantly, but it's agreed upon by the tornado community that it's not a real increase. It's having to do with better (weather tracking) technology, more population, the fact that the population is better educated and more aware. So we're seeing them more often."
Comment: Here is another perspective on the 'Global Warming' issue: