California has a long history of really stringent emissions rules because the state has densely populated areas which get thermal inversions which trap the pollution where the people are. They need to be reduculously stringent because the alternative is that people die from the pollution.

The latest round have a bunch of steadily increasing fuel economy rules designed to force automakers to switch away from fossil fuels as part of a much larger effort to stabilize the rising temperatures caused by the rising CO2 concentration which their combustion causes