From Columbia University's Earth Institute:
Ben Carson (retired neurosurgeon) believes that climate change is happening in the sense that there's "always going to be either cooling or warming going on" and has called the climate debate "irrelevant." While he has no plans to combat climate change, he does believe it's important to protect the environment. If elected, he would approve the Keystone XL pipeline and develop oil resources while also investing in renewable resources; however, he would not support any government subsidies because he feels they interfere with the free market.
Donald Trump (real estate developer) doesn't believe in climate change and asserts that the changes we see are actually just weather, unaffected by human actions. He puts climate change low on the list of problems we need to address. In 2012, Trump said global warming was a hoax created by China to make U.S. manufacturing uncompetitive. He supports regulating air pollution.
Hillary Clinton (former U.S. senator from New York and secretary of state) believes climate change is real and manmade. She has called it "the most consequential, urgent, sweeping collection of challenges we face as a nation and a world." Clinton unveiled a plan that would install half a billion solar panels across the country by 2020 (a 700 percent increase in solar capacity); and expand renewable energy (including geothermal and hydro) sufficiently to produce 33 percent of U.S. electricity by 2027. Her Clean Energy Challenge, partnering with states, cities and communities, will include incentives, competitions, and investment in transmission and R&D. Clinton is opposed to the Keystone XL pipeline and Arctic drilling and supports extending the Production Tax Credit.
Bernie Sanders (U.S. senator from Vermont) believes climate change is real and manmade. He has called it "the single greatest threat facing the planet." He and Sen. Barbara Boxer introduced climate change legislation to tax carbon and methane emissions, and he secured $3.2 billion in the economic stimulus package for greenhouse gas emission-reduction grants. Sanders voted for the national goal of 25 percent of electricity from renewables by 2025 and for the extension of the Production Tax Credit. He led the fight against the Keystone XL pipeline, and opposes fracking and Arctic drilling.
Check the others candidates' views here: "The Presidential Candidates on Climate Change"
Image: "Northwestern Glacier melt, Alaska" (NASA)