I posted the other day about the issue of safety regarding nanoparticles, particularly carbon nanotubes. It's worth noting that there's a good reason why some of the environmental groups looking at nanotechnology (such as Greenpeace(PDF)) have not asked for a moratorium on research. The environmental benefits of advances in molecular nanotechnology could be staggeringly positive. The Center for Responsible Nanotechnology blog has a great post summarizing the various ways in which nanotechnology will help protect and repair the global environment.
Environmental degradation is a serious problem with many sources and causes. One of the biggest causes is farming. Greenhouses can greatly reduce water use, land use, runoff, and topsoil loss. Mining is another serious problem. When most structure and function can be built out of carbon and hydrogen by molecular manufacturing, there will be far less use for minerals, and mining operations mostly can be shut down. Manufacturing technologies that pollute can also be scaled back.
In general, improved technology allows operations that pollute to be more compact and contained, and cheap manufacturing allows improvements to be deployed rapidly at low cost. Storable solar energy will reduce ash, soot, hydrocarbon, NOx, and CO2 emissions, as well as oil spills. In most cases, there will be strong economic incentives to adopt newer, more efficient technologies as rapidly as possible. Even in areas that currently do not have a technological infrastructure, self-contained molecular manufacturing will allow the rapid deployment of environment-friendly technology.
Building a green future will not come from the relinquishment of advanced technologies. If such a strategy was ever possible, we have gone too far in our degradation of the planetary ecosystem for it to work now. Repairing the Earth's environment, instead, will require the proper application of intelligently-designed tools and systems.