If there is a nuclear strike in the United States, the energy from the explosions will emit high levels of dust and smoke into our atmosphere. The dust and smoke will float around the Earth for up to five years before it falls back down to Earth. This will block about 90% of sunlight from reaching our planet’s surface, causing temperatures to become colder than ever, with an average temperature drop of 20 degrees Fahrenheit (10 degrees Celsius). The darkness we live in for five years will cause a global famine that could kill billions worldwide.