Continuum Season 2

In season 2 of this great show we can see the characters debating on the consequences of their time-travelling on the future they left. In this regard this show is unique in that it does embed these discussions within the plot, rather than adopting a specific approach as an axiom. In Continuum we can see the authors' approach to time travel being "discovered" by the characters at the same time as the viewers. In chapters 8 and 9 of season 2, Keira and Carlos start wondering what would happen if through time travel one would arrive to a point in time where another verision of oneself was already existing.

Up to this point the time travelling in Continuum looked like part of a loop - one that Keira is desperately trying to maintain (so she can go back to a future where things are as she left them) and the Liber8 members are trying to break (in order to avoid corporations ruling society in 2077). This was further reinforced when we were led to believe that Alec was the son of Jason, in which case we definitely would have a Terminator-style loop and scenario.

However, by the end of the season this "neat" scenario is shattered, as we (and the characters in the series) come to realise that too many things have been changed for the future to be the same. Old Alec Sadler has put in a big effort and failsafes to make sure history is changed. The Freelancers emerge as custodians of the space-time continuum and right before the end credits mention that they have managed to minimize the consequences of time-travel to "this timeline". This is a hint that in Continuum's universe loops are deemed almost impossible, and alternative timelines coexist (as opposed to history being "overwritten"). In this scenario, "this timeline" is the new timeline that was created by the trip from 2077, by the Liber8 members, Elena, Keira and, as we now know, Jason. This new timeline differs (=branches off) from the original one (which we only see as in 2077 ) from 1975, the year to which Elena arrived.

The implication is that for Keira to be able to travel back to a future which is exactly the same as she left it in 2077, she either needs to cross back to the original timeline (in which she disappeared in 2077) or ensure that despite the presence of herself and the other time-travellers, the branched-off timeline ends up being identical to the original one.

A very detailed and interesting eplanation of the coesxisting timelines in Cotinuum can be found here: http://continuum.wikia.com/wiki/Timelines