Not so in the stratosphere, which begins as low as 5 miles above the Earth and rises up to about 31 miles. Rockets need to scream through the stratosphere to the point 62 miles above the sea level, where space is conventionally said to begin. They are also the only direct source of human-created compounds above 12 miles. Because there is no rain or other atmospheric factors to wash out the black carbon in the stratosphere, black carbon would linger for 5 to 10 years or more. Moroever, rockets produce over 1,000 times more black carbon per unit of fuel than standard aircraft.