Carmichael and others also stress the need to reduce energy-intensive activities like flying altogether. The International Energy Agency, for example, has pointed to the need to reduce demand for flying through measures such as taxes on flights, as part of reaching net-zero emissions by 2050. Some campaigners and researchers have called for a policy that amounts to the very opposite of frequent flier rewards – a "frequent flier levy" whereby the more someone flies, the higher a tax they have to pay on each flight.