At a special Senate hearing Tuesday in Miami Beach, Senator Bill Nelson described south Florida as "ground zero" for climate change and its threat to coastal communities, calling for "new, innovative kinds of solutions" and warning that they won't be cheap. The coming crisis is hard to understate. Miami could have 4.8 million people and $3.5 trillion in assets at risk in a major storm if sea levels rise 0.5 meters by 2070, according to a 2008 report from the OECD.