No, the short and simple answer is no. Nothing we do is going to fix the Earth right away. The Earth is way too broken and harmed for simple and unnoticeable actions to be taken and for it to actually work at all. Cites contribute to a lot if not most of the pollution and climate change that causes harm to the earth. Sustainable cities can do a few things to help though, such as, using renewable resources, having lots of sidewalks, opting for a mass transportation system, and slowing down energy consumption.
Using renewable resources would really improve any area in the world, but definitely areas with mass amounts of people with energy surges like no other. Cities are notorious for using so much power and this would really improve the carbon footprint of cities if most cities could use renewable energy. While yes it can be very expensive to start and maintain, the benefits much outwardly outweigh the price.
Having lots of sidewalks, or bicycle trails give more opportunities for people to walk or bike places, rather than driving. While, this is not just a problem for cities, it also for people that live further out. If there are more places closer to where people are they wont need to drive, or better for the people who live farther out of town where it is not ideal to walk into town when need be they could opt for mass transportation, such as bus or carpooling. This also would help more if electric or fuel efficient vehicles were used.
Slowing down on energy consumption in cities could really help with their carbon footprints too. Not using as much energy could benefit by not having to make as much, whether that is by renewable resources or carbon resources. Just not using as much puts so much less carbon into the atmosphere, helping our carbon footprints decrease.

https://www.repsol.com/en/energy-and-th … dex.cshtml
https://www.thegef.org/what-we-do/topic … ble-cities