John McCain, Republican candidate for US President, has joined his Democratic opponent Barack Obama in explaining how his administration would tackle science, technology and the environment.

McCain has previously distanced himself from fellow Republican George Bush on scientific issues. He thinks the US should do more to combat climate change, wants more research done on embryonic stem cells, and opposes drilling in Arctic nature reserves.

But the selection of Sarah Palin as his running mate raised questions over his pro-science credentials. The Alaskan governor promotes the teaching of creationism in schools, and her church believes it is possible to 'convert' homosexuals to heterosexuality. She claimed that the "jury's still out" on whether humans cause climate change, and McCain himself has now changed his mind on offshore drilling, backing the right of individual states to explore for oil.

Although Obama answered a list of questions posed by leading figures in American science two weeks earlier, McCain's supporters will hope that his belated response can answer some of his critics. The full list of answers from both candidates can be found on www.sciencedebate2008.com.

The website is a grass-roots initiative led by a number of scientists, and it received more than 38,000 questions for the candidates from members of the public, from which 14 were chosen. These are some of the highlights from their answers.

To tackle climate change, McCain says he will introduce a cap-and-trade system with the target of a 60% reduction from 1990 levels by 2050. However, that figure falls short of the 80% recommended by the IPCC – which Obama says he would meet, using the same methods.

On energy, McCain wants market-driven renewable energy sources, and a huge (unrealistic?) expansion in nuclear power. Obama, while also backing nuclear power, has impressed the green lobby by saying he will invest in cleaner energy to the tune of $150bn over 10 years.

Both candidates support overturning President Bush's ban on creating new cell lines for stem cell research, but make clear that they favour the use of unwanted eggs from fertility clinics for the research. Obama may have disappointed many scientists by not explicitly saying he will allow the use of eggs specifically created for such research, but some were concerned by McCain's hints that he would criminalise the practice.

Obama claims that the nation's space programme is important, particularly for confronting scientific and technical problems here on Earth. McCain, though, is noticeably more enthusiastic. He wants NASA to begin a "new era" of human space exploration, and is very keen on completing the US lab on the International Space Station. Still, given his antagonism towards Russia and China, his motivations in "ensuring the US remains a leader" in space exploration could reflect concerns over those countries' extra-terrestrial activities, rather than scientific endeavour.

For now, Obama seems to be slightly more progressive on the issues. But the real praise must go to the citizen-driven ScienceDebate2008 website, for making both candidates engage with science so comprehensively.