have been shown, but the technology is too costly without a carbon tax or "cap and trade" emissions policy in place. The United States, China, and India have not agreed on emission limits, and these are precisely the countries with massive coal resources where planned buildup of conventional coal electric power stations is most intense. The lower right panel of Figure 5 shows how conventional coal plants in the works will overwhelm proposed CCS plants. A Department of Energy-funded CCS pilot plant called "FutureGen" was cited by this administration at climate negotiations in Montreal as the US premier effort, in partnership with the coal industry, to combat global warming (Revkin, 2005). But this plant is unlikely before 2012 and its location is still unannounced. Experts believe it may be more expensive to retrofit conventional coal plans with CCS than build gasification plants with CCS from scratch. Suppose global warming got bad-really bad. Will conventional coal plants be abandoned, as the $6 billion Shoreham nuclear plant was after Three Mile Island (TMI) and Chernobyl? Once they are generating electricity from cheap coal, with capital costs "sunk" for 50 to 75 years, it might be so expensive to shut Fig. 6

CAN "GREEN" NUKES SAVE THE DAY?

BUT: U 235 resources burned at 10 TW with "once through" reactors will only last 6-30 years: WE'D NEED TO START BUILDING BREEDERS NOW!

down and build new ones that ratepayers would balk even to slow a global warming juggernaut. This is not a good scenario.

Another class of low-carbon primary power now being reconsidered after a disastrous start is "green" nukes (figure 6). No one has started building a new nuclear reactor in the United States for the past 30 years, though some are planned. Classic problems of nuclear power are operational safety, waste disposal, and weapons proliferation. However, for global warming mitigation, the major constraint may be that planned reactors are "once through" and use the supply-limited uranium 235 (U235) isotope, which makes up less than 1 percent of natural uranium. The energy content of U-235 in identified deposits is less than natural gas. We would run out of fuel in 30 years employing such reactors at rates sufficient to supply present primary power demand. As with coal, we do not have the luxury of investing in the wrong nuclear power infrastructure. Longer-term, we will need to breed U-238 (99 percent of natural uranium) into plutonium or more abundant thorium to U233, a fuel I favor for several technical reasons. Why not start now? Infrastructure and weapons proliferations issues need to be faced now if we are serious about green nukes as alternative energy.

The third class of primary power, my own preference, is renewable energy, currently less than 1 percent of primary power (figure 7). Space limitations prevent an adequate discussion, but I and colleagues at the National Renewable Energy Laboratory (NREL) in Golden, Colorado, and elsewhere believe solar and wind power can be scaled up, with a proper infrastructure of transmission and storage, to provide 30 percent or more of primary emission-free power by midcentury (Pew Center, 2004). President Jimmy Carter, a strong advocate of renewables, created the Solar Energy Research Institute, the precursor of NREL. And Jerry Brown, dubbed California's "governor moonbeam" by critics, in the 1970s initiated tax and other incentives leading to the now cost-effective Altamont wind farms. It is hard to overestimate the damage done by Ronald Reagan who, on becoming president, symbolically ripped the solar panels Carter had put on the roof of the White House, likewise dismantling most of Carter's energy research and development initiative. We have not recovered. Carter's administration

a quarter century ago was the last time the US had a pro-active alternate energy policy. Unfortunately, the institutional memory of this has dimmed. Whatever the problems of Carter plan, and there were some, the United States, and because of our leadership, the world, was headed toward a sustainable energy future. Not now.

What colleagues and I propose as a goal is that by mid-century, renewables should supply roughly a third of the world's power; clean, safe and sustainable nukes another third; and coal gasification with CCS the final third. The total would amount to 100 to 300 percent of present energy demand. There are major roles for business and talented entrepreneurs, but I do not see how we get there without the stimulus of massive Apollo-like government-funded research and development, perhaps starting with ARPA-E (Advanced Research Projects AgencyEnergy; after DARDA, the Defense Research Projects Agency, which gave us, among other things, the Internet) proposed by the National Academy of Science (Committee on Science, 2005).

At the same time, we need to implement everything we have in our alternate energy arsenal immediately. I do this myself as best I

can. I drive a hybrid and get my home's electricity from green power, mainly wind power purchased by my utility from upstate New York (Hoffert, 2004). At this point, I pay a premium for this "privilege." I do not claim any special virtue as an early adopter. I do think both ethics and "cool" technology can be early drivers of alternate energy. At least until it become cost-effective to the average person, perhaps stimulated by carbon and gas taxes and/or cap-and-trade schemes. We need work on a broad spectrum of possible solutions; picking technology winners is notoriously uncertain, even by experts (Clarke, 1982).

This is not the forum to elaborate on the most innovative hightech ideas that could allow us to live sustainably on the planet. Interested readers should consult Hoffert et al. (2002) and the special issue of Scientific American on "Energy's Future Beyond Carbon" (2006). Climate and sustainable energy is a political as well a science and engineering problem. With the memory of Rick Smalley's brilliant exposition in mind (he gave a most engaging and accessible public lecture at an Aspen Global Change Institute conference that I co-organized a few years ago), I hold that energy and global warming, not terrorism and mind-numbing dogma, are the appropriate organizing principles for this century. There is no guarantee high-tech civilization will survive into an ever richer future. But I find no solace in joining with the peak oilers to hunker down to a long slow decline with a return to agrarian (and eventually hunter-gatherer?) lifestyles as energy runs down and sea levels rise (Urstadt, 2006). Likewise, keep me away from Ted Kaczynski, the "Unabomber," who would destroy even a solar-powered high-tech world (Kaczynski, 2002).

I am optmistic enough about technology to believe policies based on science and engineering can solve the climate/energy problem; that with enough effort, thoughtful energy policies, instead of the usual pork packaged for public relations, can become part of political party platforms by the next US presidential election. The stakes are high. We owe to ourselves and generations to come to fight for our remarkable technological civilization, with all its imperfections, built on the shoulders of earlier generations. It will be hard. We will need every ounce of creative imagination. If we do make it through the twenty-first century without imploding, perhaps

someday we might even find a way to cope with those problems our pretechnology evolutionary history has left us quite unprepared for.

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