In the last decade there has been a significant decrease in coffee consumption. During this same time, there has been increasing publicity about the adverse long-term effects on health of the caffeine in coffee. Ttherefore, the decrease in coffee consumption must have been caused by consumers' awareness of the harmful effects of caffeine.
The statement 'Coffee prices increased steadily in the past decade because of unusually severe frosts in coffee-growing nations' most seriously calls into question the explanation above.