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2 degrees Celsius: A critical number for climate change
01:16 - Source: CNN

Editor’s Note: CNN columnist John D. Sutter is reporting on a tiny number – 2 degrees – that may have a huge effect on the future. He’d like your help. Subscribe to the “2 degrees” newsletter or follow him on Facebook, Twitter and Instagram. He’s jdsutter on Snapchat.

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Every Friday, we'll answer your climate change questions here and on CNN International

To submit a question, go to this Google Form; you could end up on TV

CNN  — 

Each Friday, CNN will answer one of your questions on climate change, which is one of the most important (and confusing) topics that far too few of us are talking about. To submit a question, fill out this Google Form. Answers will show up here and on CNN International. In other words: Ask a question, and you could end up on TV.

This ongoing Q&A is part of CNN’s Two° series. For more, check out the Two° homepage and consider signing up for our weekly newsletter. And thank you! – John Sutter, CNN columnist

oceans food chain could collapse climate change jennifer gray mss orig_00010417.jpg
Oceans' food chain could collapse
01:26 - Source: CNN

Q: Will climate change cause an ocean food chain collapse? (October 23)

Question from William Breyer, Indian Harbour Beach, Florida

Answer by Jennifer Gray, CNN Meteorologist

Answer: Yes, according to a recent study by Adelaide University in Australia. Why? Well, we know that carbon dioxide is increasing globally and the oceans absorb huge amounts of CO2 each year. When this happens, the pH levels of the ocean are reduced. That’s because CO2 is an acid gas and when it dissolves in water, including seawater, it forms carbonic acid.

As CO2 dissolves into the oceans, it fundamentally alters ocean chemistry, making it more acidic. This acid addition is where the name “ocean acidification” comes from and is why ocean pH is declining worldwide.

One marine ecologist who has studied the issue says warmer waters are creating higher metabolic rates that, in turn, are creating a bigger demand for food.

Read more of Jennifer Gray’s detailed answer here

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Floodwater covers South Carolina neighborhood
01:32 - Source: CNN

Q: Were South Carolina floods caused by climate change? (October 8)

Question from Sital Sathia, Chicago, Illinois

Answer by Brandon Miller, meteorologist, CNN International

Answer: Attributing extreme weather events to climate change is one of the most important aspects of climate change research. It’s also controversial.

The reason for the latter: It’s difficult to prove a single weather event was “caused” by humans burning fossil fuels and warming the planet. After all, extreme weather has occurred all over our planet long before humans started interfering with the climate system. But scientists are clear that some extreme weather events are influenced by global warming.

Was the recent, devastating flooding in South Carolina caused by climate change? We don’t know for sure, at least not yet. More research is needed. But we know this event has the fingerprints of climate change all over it.

This flooding contained a combination of several extreme weather events that we expect to occur more frequently as a result of global warming – including extreme precipitation (i.e. a lot of rain falling in a short amount of time) and coastal flooding.

Read more of Brandon Miller’s detailed answer here

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Bugging out: America's first edible cricket farm
03:41 - Source: CNN

Q: Does eating bugs help fight climate change? (October 8)

Question from Torben Ørvad Jensen, Denmark

Answer by John D. Sutter, CNN columnist

Answer: A 2012 study shows that mealworms have a smaller carbon footprint, per kilogram of edible protein, than milk, pork, chicken or beef. Beef, for example, has a carbon footprint about six to 13 times the size of mealworms, per kilogram of edible protein, the study says.

Dutch entomologist Dennis Oonincx, who published the study, told me the results likely would be similar for edible crickets – which are being grown on farms as a way to help combat global food insecurity. Scientific research has not quantified exactly how much crickets contribute to climate change, although Oonincx points out that crickets likely would have a slightly larger carbon footprint, similar to that of pork or milk.

Read more of John Sutter’s detailed answer here

Q: Why don’t more conservative Christians believe in climate change? (September 25)

Question from Wayne Stoll, Ladysmith, Wisconsin

Answer by John D. Sutter, CNN columnist

Answer: “Climate change is a problem that can no longer be left to a future generation.”

That’s one religious leader – the Pope – speaking in front of the White House.

But as Wayne Stoll, our reader in Wisconsin, points out in this week’s Two° question, some conservative Christian leaders have not joined Pope Francis on this issue. Many of them don’t see climate change, as he does, as a moral outrage – and cause for urgent action.

Take the Cornwall Alliance, which wrote an open letter to Pope Francis in April urging him not to support efforts to rid the world of fossil fuels. “Such policies,” the group wrote, “would condemn hundreds of millions of our fellow human beings to ongoing poverty. We respectfully appeal to you to advise the world’s leaders to reject them.” The group, in its letter, also rejects mainstream climate science, saying computer models provide “no rational basis to forecast dangerous human-induced global warming.”

These views seem to be reflected among some churchgoers, with conservative Christians being less likely to accept mainstream climate science that says the climate is warming and humans largely are to blame. And even among religious Republicans there’s an apparent split between Catholics and Protestants. Catholic Republicans, for example, are more likely to say global warming is happening than their non-Catholic Republican counterparts, according to a survey by the Yale Project on Climate Change Communication. Catholics and nonevangelical Protestants in the United States, according to that group, also are more likely to say humans are causing climate change than evangelicals.

So how do religious climate doubters justify their views? I got a window into that earlier this year after I spent a week in Woodward County, Oklahoma, which is highly religious and, statistically, is one of the most climate-skeptical places in the United States. I met some conservative Christians in Woodward County who see climate change as a sign of the end times. They think it’s happening, but they see it as God’s punishment for an upside down world, and therefore don’t think we can or should do anything about it. Others seemed almost too humble to accept climate science. They said humans are too small – too insignificant in the face of the all-knowing, all-doing Creator – to actually alter the global climactic system. For others, rejecting mainstream climate science seems more a matter of politics.

You can hear climate doubters in their own words in this video from Woodward:

For two degrees, Woodward, Oklahoma story
Opinion: Common ground with climate skeptics
03:23 - Source: CNN

The underlying message in much of this: God is in control.

Humans can’t possibly be messing things up this bad.

But there’s a rebuttal to that argument. “The answer to that is pretty simple: It’s free will,” Katharine Hayhoe, an evangelical Christian and climate scientist at Texas Tech, told NPR. “God gave us the brains to make good choices, and there’s consequences to the choices that we make.”

Meanwhile, religious leaders of all stripes continue to call for action. Muslim scholars, for example, recently issued the Islamic Declaration on Global Climate Change, which prods world leaders to move quickly slash carbon emissions to zero.

“(W)e have now become a force dominating nature,” they write. “Our species, though selected to be a caretaker or steward on the Earth, has been the cause of such corruption and devastation on it that we are in danger ending life as we know it on our planet.”

And there’s diversity of thought among conservative Christians, too. “It is God’s love that calls all of us to take on this challenge,” says a letter posted on the website for the Evangelical Environmental Network, addressed to President Obama. “That is why we write to offer our support and encouragement for your efforts to overcome the climate challenge.”

Perhaps more conservative religious leaders will start speaking up.

Q: What do the U.S. presidential contenders think about global warming? (September 18)

Question from Randy McNamara, San Francisco
Answer by John D. Sutter, CNN columnist

Answer: We got yet another frightening glimpse this week at the CNN Republican debate of what some U.S. presidential contenders think (or don’t think) of climate science.

Here’s a back-and-forth between moderator Jake Tapper and Republican Sen. Marco Rubio, a noted skeptic of the science saying the Earth is warming and we’re causing it.

Tapper: “Sen. Rubio, Ronald Reagan’s secretary of state, George Shultz, reminds us that when Reagan was president he faced a similar situation to the one that we’re facing now. There were dire warnings from the mass consensus of the scientific community about the ozone layer shrinking. Shultz says Ronald Reagan urged skeptics in industry to come up with a plan. He said, ‘Do it as an insurance policy in case the scientists are right.’ The scientists were right. Reagan and his approach worked. Secretary Shultz asks, ‘Why not take out an insurance policy and approach climate change the Reagan way?’ “

Rubio: “Because we’re not going to destroy our economy the way the left-wing government that we are under now wants to do. We’re not going to. …”

Tapper: “I’m citing (Republican) George Shultz.”

Rubio: “Well, and I don’t – he may have lined up with their positions on this issue. But here is the bottom line. Every proposal they put forward are going to be proposals that will make it harder to do business in America, that will make it harder to create jobs in America. … Maybe a billionaire here in California can afford an increase in their utility rates, but a working family in Tampa, Florida, or anywhere across this country cannot afford it.”

The obvious irony: Florida, Rubio’s state, is among the most vulnerable to rising seas, which are associated with the increase in global temperatures caused by humans. A recent study found that if we burned all available fossil fuels, Florida would be almost completely underwater.

Rubio: “Jake, you … called me a denier. …”

Tapper: “I called you a skeptic.”

Rubio: “OK, a skeptic. You can measure the climate. You can measure it. That’s not the issue we’re discussing. Here is what I’m skeptical of. I’m skeptical of the decisions that the left wants us to make, because I know the impact those are going to have and they’re all going to be on our economy. They will not do a thing to lower the rise of the sea. They will not do a thing to cure the drought here in California. But what they will do is they will make America a more expensive place to create jobs.”

From that exchange, maybe you get a sense of how difficult it is to answer reader Randy McNamara’s question about where these presidential candidates stand on climate change. As the science about climate change become abundantly clear – the climate is warming, with potentially disastrous consequences, and human fossil fuel emissions are the main cause – U.S. presidential hopefuls have gotten better at dodging attempts to classify them. It seems none wants to be labeled a “denier” or a “skeptic,” even if their policies suggest otherwise.

Rubio, who does acknowledge climate change is happening, actually has been very clear in the past. “I do not believe that human activity is causing these dramatic changes to our climate the way these scientists are portraying it,” he told ABC’s Jonathan Karl in 2014. Other candidates have made similar, anti-science statements and then later tried to soften their stances. “The concept of global warming was created by and for the Chinese to make U.S. manufacturing noncompetitive,” Donald Trump tweeted in November 2012. He later told Tapper on CNN’s “State of the Union” that the tweet was meant to be “sarcastic.” But Trump also told Tapper he is “not a huge believer in the global warming phenomena. …”

This stuff is exhausting, right?

There are several candidates – among them Democrats Hillary Clinton, Martin O’Malley and Bernie Sanders as well as Republican Lindsey Graham – who have clearly stated that they acknowledge the reality of climate science and (crucially) would work to curb fossil fuel emissions. “When 90% of the doctors tell you you’ve got a problem, do you listen to the one?” Graham told CNN’s Dana Bash on “State of the Union” in June. “At the end of the day, I do believe that the CO2 emission problem all over the world is hurting our environment. But the solution is a pro-business solution to a lower-carbon economy.”

I’d encourage the others to make their positions that clear.

And I’d ask journalists to continue to push, as Tapper did Wednesday, for more-specific statements on whether these candidates believe humans are causing climate change by burning fossil fuels, and, if so, what would they do about it. The American public, including McNamara, our reader in San Francisco, deserves a much higher level of discourse on this crucial topic.

The CNN Library contributed to this report.

Q: Who are the 97% of scientists who believe climate change is caused by people? (September 11)

View of the bed of Jacarei river dam, in Piracaia, during a drought affecting Sao Paulo state, Brazil on November 19, 2014. The Jacarei river dam is part of the Sao Paulo's Cantareira system of dams, which supplies water to 45% of the metropolitan region of Sao Paulo --20 million people-- and is now at historic low. AFP PHOTO / NELSON ALMEIDA        (Photo credit should read NELSON ALMEIDA/AFP/Getty Images)
Where does '97% consensus' on climate change come from?
02:55 - Source: CNN

Question from Mark D., Raleigh, North Carolina
Answer by Brandon Miller, meteorologist, CNN International

Answer: We hear the term “scientific consensus” bantered about a lot when discussing climate change, and the 97% number – which refers to the percentage of active climate scientists who believe people are causing climate change by burning fossil fuels – is widely cited. There’s a NASA page dissecting and touting the figure. Even President Barack Obama tweeted it. But where does this number actually come from? And who are these “97%” scientists?

First, here’s where the number comes from: There are a few studies and surveys that have found an overwhelming majority of scientists who study climate change agree that the climate is warming and that humans are responsible for it. One of the largest and most widely referenced studies was published in 2009 by Peter Doran and Maggie Kendall Zimmerman. These researchers polled more than 3,000 Earth scientists, asking them simply 1) if they believed that the planet was warming, and 2) if human activity was a significant contributor in changing the global temperature.

The scientists came from a variety of fields within Earth science (geology, oceanography, paleontology and meteorology, to name a few). Ninety percent had Ph.D.s and 7% had master’s degrees.

Nine in 10 of the scientists said global temperatures are rising and 82% said this rise is because of human activities such as burning fossil fuels and putting more heat-trapping gases in the atmosphere. But they didn’t stop there.

To gauge the view of the scientists with the most expertise, the authors also looked specifically at responses from climate science experts – meaning those who published 50% of their research in that field. For that group, the consensus was even more striking. More than 97% agreed that humans are causing the Earth’s temperature to rise.

Two°: Five techniques of climate change denial

Researchers keep getting similar results. An exhaustive review of published research on climate change was performed in a 2013 study by John Cook. The study looked at nearly 12,000 published studies over 20 years across a number of scientific, peer-reviewed journals containing the words “global warming” and “global climate change.” Of those studies, approximately one-third stated a position on whether climate change was caused by humans, and, of those who stated a position on that subject, 97.1% of the research showed humans are causing the climate to change.

Mark D., the reader in North Carolina who asked about the 97%, also wanted to know, specifically, whether it’s fair to say climate scientists have a bias … simply because they’re climate scientists.

It’s an interesting point, but it’s worth noting that science is dedicated to independent thinking. Scientists test, replicate and question their hypotheses. And, perhaps counterintuitively, there’s actually an incentive for them to try to disprove deeply held scientific theories.

They haven’t been able to do that for climate change.

“When people say scientists promote climate change to get grant money, it is an immediate sign they do not understand how grants are funded,” Marshall Shepherd, director of the Atmospheric Sciences program at the University of Georgia, and publisher of research studies on climate change, wrote in an email. “It would actually be in the best interest of scientists to say to a funding source, ‘We don’t know if human-caused climate change is happening, so fund us to figure it out.’ “

Two°: The most climate-skeptical place in America

Scientists are trying to question our understanding of this subject, and science is all about cataloging ongoing discovery. But our very best understanding of the science overwhelmingly indicates that the climate is changing and that humans likely are to blame.

That’s shown both in the research and among the views of experts in climate science.

To wrap up, consider this: More than 200 scientific associations from all over the world, including the U.S. National Academy of Sciences, the World Meteorological Organization and the U.N. Intergovernmental Panel on Climate Change, all support this consensus.

Have a climate question? Ask it here, and your question might be answered next week.