From the picture, we can see that There's no distinct correlation between population and carbon footprint. Large cities like New York and Los Angeles only have a median carbon footprint. We can learn from those cities.

Los Angeles, through its Green New Deal, is taking a bold step towards a sustainable future. The city's plan focuses on leading the world toward a low-carbon, green-energy future. Key targets include achieving 100% renewable energy by 2045, recycling all wastewater, sourcing a significant portion of water locally, making all buildings net-zero carbon by 2050, electrifying all city buses, planting thousands of trees, creating numerous green jobs, and diverting all waste from landfills by 2050. Additionally, the plan involves innovative partnerships and initiatives, such as the Los Angeles Cooling Collaborative and bringing electric vehicles to all communities, which aim to improve public health and promote sustainable transportation​​.

In the case of New York City, the focus is on creating a sustainable urban environment that does not compromise the ability of future generations to meet their needs. The city's sustainability initiatives are grounded in the recognition of the interconnectedness of people, economic development, and the environment. Efforts include reducing air pollution and greenhouse gas emissions, ensuring drinkable water and breathable air, increasing the efficiency and reliability of the power system, and promoting healthy environments in buildings. New York City has also been making progress towards its sustainability goals, including having the cleanest air in the last 50 years, a significant reduction in greenhouse gas emissions, the near completion of a goal to plant a million new trees, and the cleanup of numerous brownfield properties for new development

Data acquired from GGMCF https://www.citycarbonfootprints.info/Moran,018) Carbon footprints of 13,000 cities. Environmental Research Letters DOI: 10.1088/1748-9326/aac72a.