Happened to me in two separate games where instituting a carbon tax drops CO2 emissions right down to zero overnight. Even a modest 20% tax rate renders the entire country carbon free. Definitely doesn’t seem realistic.
CO2 and Temperature are currently both way too easy to deal with, yeah
Car emissions limits, electric car initiative and ban low mpg cars combined reduce co2 emissions by 32%. Additionally, these max out electric car transition reducing co2 by another 25%. Would car policy reform really cut out more than half of our current emissions?
https://www.c2es.org/content/international-emissions/
According to this page, fully 72% of global emissions come from Energy, 15% of which are Transport. That actually amounts to just 10.8% of emissions from Transport. 22.3% are in Electricity & Heat.
This is as of 2013 so things might have changed a bit since.
But not all CO2 sources in the game are accounted for in the game I think. And specific countries would have very different makeups of that.