Fragile generally means something like you drop a glass on the floor from 30cm and it completely shatters. If you drop a mug on the floor from 2 meters and the handle breaks off but it still works, it's not fragile. If you hit it with a meteor and it breaks, it's not fragile.
Whenever the forces of nature hit us our tool wielding seems to matter very little.
55,000 people were displaced or evacuated in California just now, with a current death toll of <100. They didn't just move all at the same time by luck and on foot; vehicles, radio, TV, fire tracking helicopters and satellites all helped keep 50,000+ people alive in the face of a natural force. We reinforce buildings against earthquakes, we build tornado shelters, the Svalbard Global Seed vault, Dutch land reclamation dykes and countless flood defences around the world, earthquake and tsunami early warning systems, storm tracking weather satellites, and every building with lightning conductors since the 1700s.
With the spread of humans around the world, even huge events like the "imminent" Pacific North West USA Cascadia zone earthquake wouldn't affect most people. Something would have to kill 50% of humans just to take the world population down to 1972 levels. 75% of people is still higher world population than it was in 1900.
What's left? Anything which affects the globe. Climate change, which is currently being talked about in a "2C in 100 years" way which is a lot more than 20 years, and ... supervolcano emissions or massive solar flares or meteor impact. And a handwavy "if some feedback loop kicks in and the oceans acidify".
The romantic notion of 50 people in a bunker surviving and continuing the human race while the oceans turn into acid .. not gonna happen.
What about whole countries putting acid rain covers over their crops and water purifiers? One project in Israel desalinates 150,000,000 cubic meters of seawater every year, providing for 1.5 million people.
If we can plan for a colony on Mars, anything that happens to Earth it will still be hundreds of times more habitable than Mars, even if that means everyone who remains living inside some kind of habitats.
