Locust swarms fly with the wind at roughly the speed of the wind. They can cover from in a day, and fly up to about 2,000 m (6500 ft) above sea level (the temperature becomes too cold at higher altitudes). Therefore, swarms cannot cross tall mountain ranges such as the Atlas, the Hindu Kush, or the Himalayas. They do not venture into the rain forests of Africa nor into central Europe. However, locust adults and swarms regularly cross the Red Sea between Africa and the Arabian Peninsula, and are even reported to have crossed the Atlantic Ocean from Africa to the Caribbean in 10 days during the 1987-89 plague. A single swarm can cover up to 1200 km2 and can contain between 40 and 80 million locusts per km2 (a total of around 50 to 100 billion locusts per swarm, representing 100,000 to 200,000 tons, considering an average mass of 2 g per locust). The locust can live between 3 and 6 months, and a 10- to 16-fold increase in locust numbers occurs from one generation to the next.