High energy charged particles rain in on the Earth from all directions, most of them produced by the Sun. Also there are space rocks which may hit earth any time. If it weren’t for the Earth’s magnetic field we would be subjected to bursts of radiation on the ground.
Some scientists have said that the solar winds could puncture holes into the ozone layer, increasing the amount of cosmic radiation on Earth. This could prove dangerous for our health. Plus, a depleting atmosphere could cause extreme weather events and climate changes.
In other words, losing the magnetic field could be very bad. Luckily for us, the likelihood that Earth’s field will just simply disappear one day is slim.
Sources:
http://www.askamathematician.com
http://www.apexmagnets.com