This linked post describes what is happening right now and what effects it has already had. The fast melt of ice in Greenland, Arctic and the Ant Arctic, aided by glacier melts all over the world. Depending on where you live on the earth, effects of climate change can be different. We have seen violent storms in the Pacific , less in the Atlantic, some areas are hotter than normal others colder.What should be undeniable by now is something is happening and the argument should not be who caused it.
The argument now should be what actions are we going to take throughout the world. If all do not cooperate especially those heavy producers of co2 all got to get in the game. Electoral production using fossil fuels has got to be stopped , burning of rain forests to get tillable soil must stop.
The biggest impact on fixing the problem but be as simple as cutting back on wasteful uses . All manners of power saving devices are available and a little different thinking can go a long way to getting in the game.
Countries like the US who is heavily dependent on fossil fuels for human , and material transportation needs to build a new rail system that is electric, long hauls would be by this method, streetcars in the major cities as their use to be when I was a kid. A lot less electronic advertisement on the major streets of the world.
Here's where I get in trouble. To meet our energy needs to get off fossil fuels there are several choices currently available. Solar and wind with a little hydro thrown in are the best sources available now. I don't think they will be sufficient to meet our needs. I feel that we will have to rely on some new nuclear plants if for no other reason than replacement of the old retiring plants.
It's fairly simple if your not willing to do the above then you are saying you are willing to see a lot people die.
The answer to the opening question. The when is now. Take a look around the world and you can see it now.