Of course, some would say that we need to expand nuclear power generation rapidly to meet these challenges. Whether you support such an expansion or not, there are three key problems. First, building enough nuclear power stations to replace fossil fuel-fired plants would be the largest construction project ever undertaken and require the use of enormous amounts of fossil fuels. Making the necessary concrete alone would be a large new contributor to greenhouse gas emissions. That means that the initial phase of a nuclear transition would actuallyincrease the rate of fossil fuel emissions. The savings on fuel and emissions wouldn't come until much later.
Second, after the Fukushima disaster, there doesn't seem to be much appetite for such a buildout. I'll be very surprised if nuclear power generation even maintains its current level in the next 20 years as Japan and Germany abandon nuclear power. Third, the timeline for such a buildout would be measured in decades, partly because of the sheer logistics involved and partly because of the brake that regulatory approvals put on such projects. Even new, cheaper and easier-to-build designs may not help if they cannot achieve the necessary regulatory approvals promptly. The history of such approvals is not encouraging. The safest thing a nuclear regulatory agency can do is say no.
I haven't even touched on replacing the fuels which power our transportation system and provide heat for our buildings and industrial processes. Transportation offers an extraordinary challenge since 80 percent of all transportation fuel worldwide is still derived from petroleum. In the United States the number is 93 percent. Despite billions of dollars spent and decades of research, we still have no good substitutes that scale to the size necessary to replace petroleum for transportation fuel.