How can a major climate event impact the earth's population?
It cause mass destruction.
One notable climate event during the Earth's lifetime was the ice age. The ice age changed a lot of the species on Earth with many becoming extinct. If the planet were to get another ice age, the humans would most likely die out as we are not adapted to harsh and very cold temperatures, e.g we do not have fur.
Alternatively, if the temperature were to rise extremely high the humans would also probably not survive as once again we are not adapted to high temperatures.