Motor emissions could have fallen by over 30% without SUV trend, report says

Basically people will decide the price they're willing to pay and will increase their "needs" until they hit that price. Cars have gotten much more efficient, so they've gotten bigger. This is the same effect you see with highways; as soon as you build a better road more people will use it (driving further and eschewing alternative transport) until the new road is just as crowded as the old one.

Here's a better issue to pursue. From the same source, ironically:

https://www.theguardian.com/sustainable-business/2017/jul/10/100-fossil-fuel-companies-investors-responsible-71-global-emissions-cdp-study-climate-change