What this means is that installing two to three times our current nameplate capacity in the form of renewables may be required to replace existing fossil-fueled plants. So, the transition period would actually turn out to be longer than what I've calculated, perhaps 140 to 210 years using 2005 to 2009 installation figures. Of course, installations of such renewables as wind and solar are accelerating. So, that would tend to shorten this longer transition period--as would leaving existing nuclear power capacity intact. But would we be able to shorten the transition period enough to head off declines in total energy production and prevent additional serious damage to the climate?
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.