Note: This article, to be published in the October 2008 issue of Scientific American, was originally printed with the title, "Questions for Would-Be Presidents."

Add your own questions for McCain and Obama in our comments section below.

No one has ever complained that U.S. presidential candidates talk too much about science, and this year has been no exception. Nevertheless, science-related issues such as energy and health care, once viewed as sideshows, have taken center stage in this election. The candidates’ positions are often vague, but they are an improvement on past campaigns. Here are some follow-up questions that they invite.

Energy

Both John McCain and Barack Obama have called for a cap-and-trade system to cut carbon emissions, although Obama’s proposed reduction (80 percent from 1990 levels by 2050) is larger than McCain’s (65 percent). Both candidates, however, need to answer a crucial question: Why cap-and-trade when so many policy experts, seeing the troubles with carbon trading in Europe, now recommend a simpler carbon tax?

Both candidates oppose Yucca Mountain, the controversial proposed nuclear waste dump. McCain has advocated an “international repository” instead. What is the difference? Where does Obama propose to put the waste? The U.S. has spent 30 years studying Yucca; switching sites will restart the clock. What will nuclear plants do with all their spent fuel in the meantime?

Beyond these generalities, the candidates diverge. McCain would subsidize the construction of 45 new nuclear reactors, costing upward of $270 billion and taking 20 years to complete. Why invest that much public money in nuclear rather than solar or wind power, which could start pumping out watts much sooner? How would offshore oil drilling, which McCain has urged, help wean the nation off fossil fuels?

Obama has spelled out intermediate milestones for emissions reductions and specific targets for biofuels and other renewables. How would these goals be enforced? He has promised $150 billion over 10 years for energy research and development as well as a $10-billion-a-year venture capital fund. What would stop that money, as in so many past efforts, from being allocated by lobbyists rather than engineers? Does the energy industry really need more venture capital? Oddly, he has promised to “fight the efforts of big oil and big agribusiness to undermine” corn-based ethanol. How has agribusiness sought to undermine corn ethanol? If anything, it seems rather the opposite. And why sustain support for corn ethanol when it is the most ungreen of all biofuels?

Embryonic stem cells

Both McCain and Obama support harvesting stem cells from embryos left over from in vitro fertilization. McCain would ban scientists from using donor eggs to create disease-specific stem cell lines or chimeric animals to see how human stem cells behave during development. How, then, would his policy be substantially different from the current highly restrictive one, and how would it encourage the discovery of lifesaving treatments? As for Obama, what alternative sources of embryonic cells would he permit? What federal oversight should embryonic stem cell research have that other forms of biomedical research, including those involving human subjects, do not already have?

Space

Both candidates support President George W. Bush’s plan to send astronauts to the moon and then to Mars. Are McCain and Obama willing to increase NASA’s budget commensurately, or would they beggar the space science programs?

Other topics

Obama, more than McCain, has taken positions on many other science issues. He has promised to double federal funding for basic research. Over what period? And does that figure include his promised energy investment? He has said he would appoint a chief technology officer to protect citizens’ electronic privacy, but could that person really overrule federal agencies with their own prerogatives? How precisely would Obama make good on his vow to reform the troubled copyright and patent system? Both candidates clearly need to flesh out their ideas if those ideas are to rise above throwaway campaign pledges and become real policy.