Is it possible for Earth to experience Polar Shift?
Is it possible for Earth to experience Polar Shift?


Yes, and it has happened before.

In the past 80 million years it happened over 150 times. The last time this happened was around 800 thousand years ago. A quick note about what a polar shift is, more properly termed a geomagnetic reversal. Earth's magnetic is such that a compass points to a certain direction. For example, a modern compass would point north. In a reversal, it would point south instead because the poles are reversed. Without going too much into detail, this occurs not by spinning of the poles but rather by decreasing in intensity until it becomes negative, thus reversing the poles.

Another important thing is the intensity. A strong magnetic field shields Earth's from some kinds of radiation, for example the stuff you can see in Gordon's answer. However, a reversed but strong magnetic field is just as fine. What you should be worried about is the change in the intensity of the field, and this is going up and down all the time, quite rapidly as you can see in the following figure:



The black bit (called Brunhes) is now - when the magnetic field is "normal". The white field in the bottom is more than ~780 thousand years ago, when it was reversed (called Matuyama). As you can see, even though the magnetic field has been normal though this entire time, the intensity went up and down. So yes, a reversal would mean that at one point the intensity would be very low, but this can happen even without a reversal.


  What would be the possible effect to human beings if this happens?


In contrast to what some people on the Internet claim, there would be no earthquake or volcanoes or other scary stuff related to it. This is simply not how this works. Also, mass extinctions from the geological history are not correlated with geomagnetic reversals, so you can take that worry off your mind. What can happen is detailed in a good way in Gordon's answer. Nothing too scary.


  Magnetic Field of the earth is seriously degrading for the past centuries and we are currently in the process of the so called Polar Shift


Not necessarily. It seriously degraded many times before without associated geomagnetic reversals.