[Heff]

Our goose is not cooked. But it could have been.

What's the worst that could happen to earth and us humans with one or two of these flares?

[Lawdoc]

By and large we are OK because of the Earth's magnetic field acting to protect us.

Some have speculated that if there were a flare of sufficient size (this one does not even come close to qualifying) it could destroy the atmosphere and make the planet uninhabitable. Again, this flare is not the so called "kill shot" some have worried about.