The true scale of how these mountains are mined is only visible from the air.

BBC: Climate chaos: Transcript

But I would love a future of no tailpipe emissions, no brown air visible as I approach downtown Houston every day.

FORBES: How To Roll Like A Republican

Although barely visible in the air, the ash -- made up of tiny particles of rock, glass, and sand -- poses a serious threat to aircraft, stalling engines and causing electrical failure, experts have said this week.

CNN: Air travel paralyzed as volcanic ash cloud lingers

At Finse station, passengers climb down to the platform with packs and sturdy boots, their breath visible in the cold mountain air.

BBC: The perfect trip: Norway

This waste produces pollution on land, sea and air and is not always visible - it needs to be reduced not just PICKED UP.

BBC: Overflowing bin

This is most visible over a 2006 plan to move Futenma, the air base on Okinawa for America's marine expeditionary force.

ECONOMIST: Banyan

The AAIB stated the works on the runway were also not easily visible to the crew at the start of take-off and the captain said that air traffic control provided no additional warnings.

BBC: Essex