Are you saying we need Houston and New Orleans because of their importance to the energy industry? The same energy industry that's causing global warming.
Most of the Midwestern agricultural products exported overseas get transshipped from river barges or trains to oceangoing ships at New Orleans. Likewise, Houston is a major container port for finished goods. We need these ports for their value as ports. Condemning these ports over some moral judgement for a portion of their throughput shouldn't have any bearing on this kind of cost-benefit analysis.