When it comes to climate science, two of the three Democratic presidential candidates are 'A' students, while most of the Republican contenders are flunking, according to a panel of scientists who reviewed candidates' comments.
At the request of The Associated Press, eight climate and biological scientists graded for scientific accuracy what a dozen top candidates said in debates, interviews and tweets, using a 0 to 100 scale.
To try to eliminate possible bias, the candidates' comments were stripped of names and given randomly generated numbers, so the professors would not know who made each statement they were grading. Also, the scientists who did the grading were chosen by professional scientific societies.
Former Secretary of State Hillary Rodham Clinton had the highest average score at 94. Three scientists did not assign former Maryland Gov. Martin O'Malley a score, saying his statements mostly were about policy, which they could not grade, instead of checkable science.
Two used similar reasoning to skip grading New Jersey Gov. Chris Christie and one did the same for businesswoman Carly Fiorina. Republican Sen. Ted Cruz of Texas had the lowest score, an average of 6. All eight put Cruz at the bottom of the class.
"This individual understands less about science (and climate change) than the average kindergartner," Michael Mann, a Pennsylvania State University meteorology professor, wrote of Cruz's statements. "That sort of ignorance would be dangerous in a doorman, let alone a president."
Vermont Sen. Bernie Sanders, with an 87, had the lowest score among the Democrats, dinged for an exaggeration when he said global warming could make Earth uninhabitable. Former Florida Gov. Jeb Bush scored the highest among Republicans, 64, but one grader gave him a perfect 100. Bush was the only Republican candidate who got a passing grade on climate in the exercise.
Below Clinton's 94 were O'Malley with 91; Sanders, 87; Bush, 64; Christie, 54; Ohio Gov. John Kasich, 47; Kentucky Sen. Rand Paul, 38; Fiorina, 28; Florida Sen. Marco Rubio, 21; businessman Donald Trump, 15; retired neurosurgeon Ben Carson, 13; and Cruz with 6.
For the Republicans, climate change came up more in interviews than in their four debates. But Rubio did confront the issue in the Sept. 16 debate in a way that earned him bad grades from some scientists.
"We are not going to make America a harder place to create jobs in order to pursue policies that will do absolutely nothing, nothing, to change our climate, to change our weather, because America is a lot of things, the greatest country in the world, absolutely," Rubio said. "But America is not a planet. And we are not even the largest carbon producer anymore. China is. And they're drilling a hole and digging anywhere in the world that they can get ahold of."
Scientists dispute Rubio's argument that because China is now the top emitter, the U.S. can do little to change the future climate. The U.S. spews about 17 percent of the world's carbon dioxide emissions, "so big cuts here would still make a big difference globally," said geochemist Louisa Bradtmiller at Macalester College in St. Paul, Minnesota. Rubio's inference that China is not doing much about global warming "is out of date. The Chinese are implementing a cap-and-trade system in their country to reduce emissions," said Andrew Dessler, a climate scientist at Texas A&M University.
At an August event In California's Orange County, Cruz told an interviewer, "If you look at satellite data for the last 18 years, there's been zero warming. ... The satellite says it ain't happening."
Florida State University's James Elsner said ground data show every decade has been warmer than the last since the middle of the 20th century and satellite data-based observations "show continued warming over the past several decades."
In fact, federal ground-based data, which scientists said is more reliable than satellites, show that 15 of the 17 years after 1997 have been warmer than 1997 and 2015 is on track to top 2014 as the warmest year on record.
Scientists singled out Sanders for overstatement in the first Democratic presidential debate.
"The scientific community is telling us that if we do not address the global crisis of climate change, transform our energy system away from fossil fuel to sustainable energy, the planet that we're going to be leaving our kids and our grandchildren may well not be habitable," Sanders said.
Dessler said, "I would not say that the planet will become uninhabitable. Regardless of what we do, some humans will survive." Harvard's Jim McCarthy also called the comment an overstatement, as did other scientists when Sanders said it. Recent research on the worst heat projections in the hottest area, the Persian Gulf, finds that toward the end of the century there will be a few days each decade or so when humans cannot survive outside, but can live with air conditioning indoors.
Trump brought out some of the more colorful and terse critiques.
"It could be warming and it's going to start to cool at some point," Trump said in a September radio interview. "And you know in the 1920s people talked about global cooling. I don't know if you know that or not. They thought the Earth was cooling. Now it's global warming. Actually, we've had times where the weather wasn't working out so they changed it to extreme weather and they have all different names, you know, so that it fits the bill."
McCarthy, a former president of the American Association for the Advancement of Science, called Trump's comments "nonsense," while Emmanuel Vincent, a climate scientist at the University of California, Merced, said, "the candidate does not appear to have any commitment to accuracy."
The eight scientists are Mann, Dessler, Elsner, McCarthy, Bradtmiller, Vincent, William Easterling at Pennsylvania State University and Matthew Huber at the University of New Hampshire.
"What We Know" on climate science by the American Association for the Advancement of Science on climate science: http://bit.ly/ZxACVI
"Climate Change: Evidence and Causes" by the U.S. National Academy of Sciences and Royal Society of United Kingdom: http://bit.ly/1pufueQ