Obama would double federal spending on basic research, help more Americans get on the Web, and spend $18 billion on education initiatives including precollege math and science, paid for in part by delaying NASA's return to the moon and Mars exploration (projects, ironically, that employ thousands of scientists and engineers). He supports a market-based carbon-trading system to cut carbon emissions to 80% below 1990 levels by 2050 and wants to invest $150 billion to develop biofuels.

Edwards would end censoring research and slanting policy on climate change, air pollution, stem cell research and would increase science funding. He would oppose expanding nuclear power and proposes to cut greenhouse gas emissions by 80% by 2050, using a cap-and-trade system to auction off permits as a regulatory incentive.

Huckabee has in the past called environmentalists wackos, and claimed he doesn't believe in evolution. In a presidential debate and in a television interview he sidestepped questions about whether climate change is caused by humans, though in a May debate he said "Our responsibility to God means that we have to be good stewards of this Earth."

McCain views global warming as "the most urgent issue facing the world" and makes climate change on of the top issues of his campaign, writes Constance Holden. On the human embryonic stem cell issue, "he draws the line at human nuclear transfer, or research cloning, arguing that there is no ethical difference between cloning for research and cloning for reproduction."

Romney, as Massachusetts governor, said "we want to make sure we are at absolutely the front edge" of stem cell research. He launched an effort to lure more high-tech talent into the state and joined with seven other Northeastern states on a regional plan to reduce carbon dioxide emissions at power plants—the first collective U.S. effort to control greenhouse gases. He also consistently opposed efforts to introduce the teaching of intelligent design in the classroom.

Giuliani's campaign "successfully discouraged key advisers from speaking to Science about specific issues," writes Eliot Marshall. On abortion, he would, with reservations, let the woman decide what to do. The League of Conservation Voters reports that Giuliani has "no articulated position" on most of the environmental issues it tracks.

Julia Whitty is Mother Jones' environmental correspondent. You can read from her new book, The Fragile Edge, and other writings, here.