Climate change and concerns over regulations on greenhouse gas emissions are some of the most controversial political issues facing the 2016 presidential candidates.
While some strongly deny the mainstream scientific consensus that the Earth is experiencing a period of global warming, many of the candidates in the running have different views on how to address the issue in a way that will protect the American economy, while still ensuring a brighter future for the planet and future generations.
Take a look at the views each 2016 presidential candidate has on climate, the energy industry and their stance on the Keystone XL oil pipeline.
JUMP TO: Full guide to Democratic candidates | Full guide to Republican candidates
Take a look at what each Democratic hopeful has said on these issues:
Former Secretary of State Hillary Clinton has been one of the most outspoken candidates in her views on climate change and her support of clean, renewable energy infrastructure.
"The reality of climate change is unforgiving no matter what the deniers say," Clinton said in a July New York Times article.
Clinton has continually voiced her opinion on the issue of climate change and is calling for actions not only to support the growth of renewable energy sources from solar energy and wind but also to end tax subsidies for the oil and natural gas industries.
Part of Clinton's plan is to have 500 million solar panels installed, reduce greenhouse gas emissions by 30 percent by 2025 and by upwards of 80 percent by 2050, according to her campaign website.
Clinton is a supporter of the EPA's Clean Power Act. She wants to revitalize coal communities by creating new jobs and industries.
After months of avoiding her stance when asked about the Keystone XL pipeline, Clinton announced her position at a campaign event in Iowa in September.
"I think it is imperative that we look at the Keystone XL pipeline as what I believe it is: a distraction from the important work we have to do to combat climate change and, unfortunately from my perspective, one that interferes with our ability to move forward and deal with other issues," she said. "Therefore, I oppose it."
Vermont Sen. Bernie Sanders has been ranked as a "Climate Change Hawk," according to a May Huffington Post article, citing his strong stance on bringing congressional attention to the issue.
In 2013, Sanders sponsored legislation on climate change that would tax carbon pollution emissions and would fund investments in energy efficiency and sustainable energy technologies as wind, solar, geothermal and biomass.
"Enough is enough. It's time for a political revolution that takes on the fossil fuel billionaires, accelerates our transition to clean energy and finally puts people before the profits of polluters," Sanders stated on his website.
Sanders' goal is to cut carbon emissions by 40 percent by 2030 and 80 percent by 2050. Like Clinton, Sanders has a comprehensive plan to reduce greenhouse gas emissions and support the development of clean, renewable energy infrastructure.
When it comes to his stance on the Keystone XL pipeline, Sanders has not been afraid to say what's on his mind.
"If you're concerned about climate change, say 'no' to the Keystone XL pipeline," Sanders said at the news conference in August 2015, stating the pipeline would ship some of the dirtiest oil on the planet from Canada's tar sands region to refineries in Texas.
Take a look at what each Republican hopeful has said on these issues:
When it comes to climate change, the billionaire investor, entrepreneur and television personality, Donald Trump, has publicly said he does not believe it is a real phenomenon on more than one occasion, even calling it a hoax.
In a 2015 interview with talk show host Hugh Hewitt, Trump stated his views on climate change and said he did not believe in it, but he also said that he feels weather patterns change over time.
"Obama thinks it's the number one problem of the world today. And I think it's very low on the list. So I am not a believer, and I will, unless somebody can prove something to me," he told Hewitt.
In 2011, Trump tweeted at President Obama regarding an increase of the EPA's budget, stating "the EPA is an impediment to both growth and jobs. It sends jobs overseas."
He has also been critical of the White House saying, "The White House continues to defend the billions it pissed away on ‘green energy' failures," in 2013.
While a proponent of the natural gas, oil and coal industries, he has called wind energy "unreliable and terrible," stating "windmills are destroying every country they touch," in a 2012 tweet.
Like the other Republican presidential hopefuls, Trump is also a supporter of approving the Keystone XL oil pipeline, citing a need for energy independence and the creation of American jobs.
When compared with the other Republican presidential hopefuls, Texas Sen. Ted Cruz may be the most outspoken in his skepticism about climate change.
In October, Cruz said climate change was "not science, it's religion," during an interview with Glenn Beck.
In a December 2015 NPR interview, Cruz said, "in the debate over global warming, far too often politicians in Washington - and for that matter, a number of scientists receiving large government grants - disregard the science and data and instead push political ideology."
While Cruz has been consistently skeptical about climate change, he maintains his support for alternative and renewable energy sources.
"I fully expect in a hundred years, or maybe 50 years, or maybe even 10 or 20 years - I mean, change can be very rapid. And I am excited to see where that goes. But it will come from the private sector, not from government," he told NPR, citing alternative energy innovations, but stressed they will not come from Washington.
Cruz is a proponent of approving the Keystone XL oil pipeline, citing the potential for job growth in America.
"If your concern is the environment, the last thing you want to do is send that oil to China to be refined there, which will be far more damage to the environment than refining it in the U.S., where it would generate good, high-paying jobs," Cruz said at a Heritage Action's Conservative Policy Summit in 2014.
The retired John Hopkins Hospital neurosurgeon finds the issue of climate change irrelevant, but that doesn't mean he doesn't support environmental protection.
"There's always going to be either cooling or warming going on. As far as I'm concerned, that's irrelevant. What is relevant is that we have an obligation and a responsibility to protect our environment," he said in a 2014 interview.
Carson stated he wasn't convinced of either global warming or global cooling, adding that he found the issue to be a distraction. In addition, he said he believes the EPA should work with industries and universities in developing environmentally friendly energy infrastructure.
Ohio Gov. John Kasich has stated that he believes climate change is a problem that needs solving but does not support EPA regulations for emissions.
"I am a believer - my goodness I am a Republican - I happen to believe there is a problem with climate change. I don't want to overreact to it; I can't measure it all, but I respect the creation that the Lord has given us and I want to make sure we protect it," Kasich said at an energy conference in 2012.
At the same conference, which was hosted by The Hill in 2012, Kasich was critical of the EPA and showed his support for the development of carbon capture for coal, according to The Hill.
"We are going to continue to work on cleaning coal, but I want to tell you, we are going to dig it, we are going to clean it, and we are going to burn it in Ohio, and we are not going to apologize for it," he said.
Despite his views on climate change, Kasich stated that solving the problem should be conducted in a way that preserves American jobs and does not stifle economic growth.
Kasich is a supporter, along with 23 other Republicans, who urged President Obama in 2015 to sign a bill approving the Keystone XL pipeline.
Florida Sen. Marco Rubio said in January that climate change was not a hoax, but he does not believe human activity has contributed to its occurrence.
In 2014 on ABC's "This Week," Rubio said, "I do not believe that human activity is causing these dramatic changes to our climate the way these scientists are portraying it. I do not believe that the laws that they propose we pass will do anything about it, except it will destroy our economy."
While Rubio believes climate change is a natural occurrence, he is in favor of lifting America's crude oil export ban and ending the EPA's Clean Power Act.
"I will stop the EPA's Clean Power Plan, which, if enacted, would have a devastating impact on affordable energy in exchange for little to no environmental benefit. It would truly be one of the most expensive and costly regulations ever created," he said in a September 2015 press release.
When it comes to the Keystone XL pipeline, Rubio is a supporter for its immediate approval, stating "President Obama's decision not to move forward on the Keystone pipeline is a mistake," in 2012.
Sources: PBS, NPR, Washington Post, Huffington Post, Bloomberg and The New York Times.