Imagine lounging at the beach, cold drink in hand, when a colossal, apocalyptic wave starts to crash in…from the sky?! That’s what happened to beachgoers in Portugal last week when a jaw-dropping “roll cloud” sent them fleeing for their lives.

Captured on video and subsequently spread across the internet, the panic was triggered by a monstrous, dark cloud barreling in like an airborne tsunami.

While it resembled the cloud from which the alien ship in Independence Day emerged, experts were quick to reassure everyone that it was not an alien invasion occurring at roughly the same time as the one in ID4; it’s just the Earth’s climate doing weird stuff.

Roll clouds, as they’re called, are long, tube-like cloud formations that cruise just above the ground. They’re rare, usually spotted over the vast, empty skies of Australia. But this one made itself known to those on the Iberian coast thanks to a record-smashing heat wave gripping Europe, where temperatures in Portugal hit a miserable 116°F.

“They look scarier than they really are,” climate scientist Paulo Ceppi told The Washington Post. Roll clouds form when cold air slams into hot, dry conditions, which is the exact meteorological cocktail Portugal’s been suffering through this summer.

When those forces combine, a wave-shaped cloud rolls over the landscape, but never breaks like a real ocean wave. Its bark is bigger than its bite because it is, ultimately, just a cloud — a cloud that is as terrifying as it is beautiful, but still just a cloud.

Roll clouds are rare, but may not be for much longer, as Ceppi warns that we might start seeing more of them popping up outside of their usual haunts like Australia, thanks to climate change upending our concept of what “normal” weather looks like.

Somehow, the gigantic, terrifying cloud of doom is the least scary thing about climate change that we’re going to have to get used to unless we start doing something about it.