The first step of any research project is picking the right topic. In this case, you need to choose at least one city and possibly several to research in-depth. You can decide which cities might be worth your time by doing some quick exploring. Unless you want to build a real-life Atlantis, this probably means beginning with checking how melting ice will affect the coastlines. Once you know if your city will still be above water, begin brainstorming and looking at other climate risks.