The US Air Force evacuated nine planes from Offutt Air Force Base in Nebraska because of flooding this week.

One of those planes was an E-4B, an airborne command-and-control aircraft vital to national defense.

The flooding and the evacuations illustrate the challenges posed to the Pentagon by climate change.

Flooding at a US Air Force base in Nebraska that damaged buildings and forced the removal of a plane integral to US nuclear-attack response highlights the risks climate change poses to national security, experts said Monday.

US President Donald Trump has repeatedly questioned whether humans cause climate change and has been angered by assessments from his military and intelligence agencies that say the phenomenon poses national-security risks.

Last week's "bomb cyclone" storm flooded about 60 structures including 30 buildings at Offutt Air Force Base, said Ryan Hansen, a spokesman for the 55th Wing, a unit that provides reconnaissance, intelligence, and combat support.