7 Billion Persons Need 7,000,000,000,000,000 (7x1015) kilocalories/year

2740 kcal x 365 days = ~1,000,000 (10⁶) kcal per person-year

1,000,000 (10⁶) kcal per person -year x 7,000,000,000 (7 x 10⁹) persons = 7,000,000,000,000,000 (7 x 10¹⁵) kcal/year