a) I think we learned a lot in the past hundred years about our climate and about the climate change(s) so if we could turn back the clock, the most important thing would be to inform the people about all the correlations, the climate and the greenhouse effect. Global actions will start as soon as this theme becomes a political issue.
b) With informations from the past we can see for example that the world is heating up the past years, the ice is melting all over the world, the water level raises... and the archives also show that this is not going to change soon.
Dave
myclimate.org