With oil prices and global temperatures rising, the nuclear option has once again entered discussions about the future of the world's energy supply. Piggybacking on the growing awareness of global climate change, the nuclear industry in the United States, Russia, and elsewhere has launched a new public relations campaign, marketing its services in the interest of clean, environmentally sound energy. In contrast to similar proposals from the 1950s, technical feasibility and economic profitability seem to be taken for granted, whereas concerns about safety and nonproliferation have gained significance. The nuclear industry today promotes new, "inherently safe," and proliferation-resistant reactor designs, improved methods of personnel training, and cost-effective standardization, along with strict licensing procedures under independent regulatory agencies. Thus, in addition to legal provisions, the industry advocates a series of "technical fixes" to prevent nuclear proliferation. The unresolved problems of radioactive waste and lingering public opposition to nuclear power are either left out of the picture, or countered with unswerving technological optimism.

This article looks at differences and similarities between current and past proposals for developing a civilian nuclear industry. It provides some historical background - particularly on the Soviet experience, which the author has explored in some depth elsewhere. Although recent proposals continue to advocate the normalization of nuclear energy on the basis of its further commercialization, a reflection on past successes and/or failures is largely missing from current discussions. A cautious reading of recent enthusiastic endorsements of nuclear energy would be well-advised.

During three decades spent studying the highly charged issue of climate change, I've not been bashful about offering my scientific conclusions - or even my opinions about appropriate public policy. Acting both as a research scientist and as a policy advocate poses some special challenges, and prominent among them is the matter of dealing with the press.

To my mind, the popular media haven't done the best job of covering the science behind this contentious topic. The roots of their difficulties are easy to understand. The first problem is their need for brevity: They have little time on the air, or space on the page, to delve into details. In addition, in covering controversy, especially when there are polarized political positions, journalists generally strive to report "both sides." Got the Democrat? Better get the Republican, too. Doing so ostensibly provides journalistic balance. But achieving the same evenhandedness in describing complex questions typical of science can be considerably more difficult, because there are rarely two mainstream views on any given subject. There may be a complete spectrum of reasoned opinion - or there may be considerable consensus among knowledgeable experts, with the only dissenting voices coming from a few extremists or special interests.

Still, many reporters have been trained to "get both sides." So by agreeing to an interview, a scientist risks getting his or her views stuffed into one of two boxed storylines. In the case of my specialty, climate change, it's either "you're worried" or "it will all be okay." In talking to reporters, I routinely discuss a wide range of possibilities.

This report outlines the changes in energy supply that will be required over the next fifty years. I describe the ultimate objective of controls on greenhouse-gas emissions and set a stabilization target for greenhouse-gas concentrations that is designed to achieve this objective. I translate this target into limits on the emission of carbon dioxide and the burning of fossil fuels over the next century, and estimate requirements for carbon-free energy supply over this period. Finally, I describe options for achieving this transformation in world energy supply and outline near-term research and development priorities.