The Carbon Footprint Planning Tools and Scenarios webpage of the Cool Climate Network of UC Berkeley has a tool for calculating how much of a contribution various local policies and actions could make to reducing greenhouse gas emissions (GHG). For Sacramento County, the graph produced is:

What is the leading category? Urban infill, which is primarily but not entirely housing. Electric vehicles, the solution most touted by agencies and politicians, comes in fifth.
This finding tracks with other analyses:
- The Weight of Cities – UN Report on Dense Infill Housing as Climate Solution https://cayimby.org/weight-of-cities-un/
- Right Type, Right Place: Assessing the Environmental and Economic Impacts of Infill Residential Development through 2030 https://www.law.berkeley.edu/research/clee/research/land-use/right-type-right-place/
Many cities in the region, including Elk Grove, Rancho Cordova, Folsom, and Roseville, and the county of Sacramento, envision of future of continuously expanding greenfield development, which is the exactly opposite of infill. Why? Because greenfield developers make bigger contributions to candidates than infill developers, and greenfield development is the perfect way of gaining property tax income now, while deferring maintenance to the future, when current office holders will be long gone. Greenfield development is climate arson, simple as that. Yes, the developments may have nice walking and bicycling paths within them, but travel to jobs, grocery stores, coffee shops, medical services, and really anything people want, requires driving a motor vehicle. As you well know, we already are not able to maintain our transportation system because most of the money goes to building more roadway capacity (particularly very expensive freeways and interchanges), not to maintenance. If what has already been built were maintained to high standards, your tax rate would be about half your income.
The answer is residential infill. That does take some investment. Some utilities may need to be upgraded. We may need to spend more on transit. But the costs are far far lower over the life of the development than is greenfield development.
Some recent articles and research on the different costs of infill and greenfield, but if you search online, you will find almost unlimited references, with a few that come to other conclusions.