At least seven people have died as more than 50 tornadoes swept across parts of the South and eastern United States over the last two days. The extreme weather has destroyed hundreds of homes and forced the closure of schools and government offices. At least four people have died in Virginia, including a two-year-old boy. Virginia Governor Terry McAuliffe has declared a state of emergency. Scientists have linked an increase in the intensity and deadliness of tornadoes to climate change.