The Earth’s magnetic field derives from motions of molten metal in the Earth’s outer core. This liquid metal, mainly Fe but some Ni and a sprinkling of other elements such as O, S, C and maybe others is electrically conducting. When an electrically conducting fluid moves, a magnetic field is set up. This magnetic field operates on the fluid and so a self-generating dynamo gets set up. The Earth’s magnetic field can be likened to a bar magnet in the center of the core… and the intersection of the bar magnet axis with the Earth’s surface gives the North and South Magnetic poles on Earth.

The humans on the surface have no effect on the generation of Earth’s magnetic field.

The Intensity and orientation of the Earth's field is not constant. There are occasions going back hundreds of millions of years, probably billions of years, where the intensity of the field suddenly decreases in intensity over 100 to 1000’s of years and the direction of the poles flips. We speak of normal and reverse polarities. The last time this happened was about 700,000 years ago. On shorter time scales there are more minor changes in the orientation and intensity of the field.

The Earth's magnetic field is caused by electric currents in the Earth's liquid outer core, which is thought to be composed of an iron-nickel alloy. This is a natural process and humans have nothing to do with its cause.

We have changed Earth in many ways, but we don't have the power to change Earth's magnetic field, which is generated 1,800 miles (3,000 km) below our feet in the liquid iron core.

Here's a nice link about changes in Earth's magnetic field.