Nasty winter tornadoes — like the deadly ones last week that hit five states — are likely to be stronger and stay on the ground longer with a wider swath of destruction in a warming world, a new study shows.

The combination of a longer and wider track with slightly stronger winds means some rare winter tornadoes that are killers now will have nine times more the power by the end of the century if carbon dioxide levels continued to rise, according to a study presented at the American Geophysical Union conference Monday.

The study, which pre-dates the devastating Mayfield, Kentucky, tornado outb...