Power generation and transportation are two critical areas, no doubt.  Another are in which mass scale concerted action is really necessary is in eco-remediation, particularly of waterways and coastlines.

1 - Reducing the toxin flow, by eliminating agricultural and industrial toxin releases into rivers, lakes, and oceans.  This would require a rather massive re-organizaiton of the agricultural technological and labor system, and a level of industrial supervision that's more or less unprecedented.  A lot needs to be done about topsoil erosion as well - and beyond that, the active organic generation of soil in an accumulative manner, for stable long-term agricultural productivity.

2 - Creating the ecological infrastructure to deal with existing pollution and continuing runoff in a productive way, via wetland filters, active bio-remediation (like the canal cleaner gmoke posted about a while ago), and other eco-oriented runoff management.

3 - Managing coastline development, nutrient outflow, and littoral zones so as to maximize the health (and marine-food productive ability) of the coasts.

4 - End the use of the ocean as a garbage dump, and move towards the active removal of already-present garbage and pollutants from the ocean.  This is such a massive project that it's hard to imagine any but the most massive worldwide efforts having any impact, but it's something to think about.

Even if we give up on the existence of any true wildlife, and accept that every ecosystem is going to be a domesticated and managed affair, it's still going to take a ton of work to make even such a minimal state of affairs possible.  The way things are going now, the eco-death of global coastal zones looks possible, if not likely.