First off, the trailer has all the scary bits. Most of the presentation is done in measured, rational tones. The trailer is trying to get people into the theatre, remember.
Secondly, the trailer doesn't show all the data that the film shows. As an example, the trailer says la la la the hottest years on record have been in the last ten years la la la. At that point, my best friend turned to me and said, but we've only been measuring temperature for 120 years. And that's fair. So it's further information when you go to see the film and learn about how temperature and CO2 levels have been measured going back 650,000 years.
Finally, the trailer doesn't show the plot twist where Gore talks about what we can do as individuals and as nations. That to me is the core of the film.
There are other plot twists not shown in the trailer, but I'd get in trouble for revealing spoilers if I told you about them.