Here's a bit of a mind fuck for you.
If you went to the past there are a number of possible results for the existence of humanity. Before we go into this I'd just like to point out that we're not that important in the grand scheme of things and calendar-hopping won't make a difference to the rest of the universe.
Now, the first possibility is that by saying something in the past, you would alter the future, or your pre-hop 'present'. This could mean you stop Hitler causing all sorts of economic and technologic advances to simply disappear, or you could be ignored as a lunatic and have little or not effect. Of course, there's a lot of grey area.
Second possibility is that in returning and surrendering information you create an alternate dimension in which the people are aware of this and act differently to the dimension from which you came. Any return to your original timeline will not show any change because you have not shifted its path, rather a turn-off.
The final option is the real mind-fuck. If such things are pre-determined then you have already gone back to the past and surrendered all the information you are or are not about to. The way that humanity reacts to this information has, according to your personal timeline, already played out and resulted in the 'present' from which you came. As such, you alter nothing, but instead fulfil your necessary role as was set out in a possible past-future loop and which you will endlessly re-do with each passage of that point in time.
For myself, I'd consider my options and surrender nothing, instead try to return to my previous present.