At the second democratic debate on Saturday, presidential candidate Bernie Sanders was asked whether he still believed that climate change was the top national security threat to the United States. Sanders stood by the statement, describing the relationship between global warming and terrorism.

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"Climate change is directly related to the growth of global terrorism," Sanders said. "[Countries] are going to be struggling over limited amounts of water, limited amounts of land to grow their crops, and you're going to see all kinds of international conflict."

Because oil revenue is one of the largest sources of income for extremist terrorist groups such as the Islamic State, Sanders argued that the world's continued dependence on non-renewable fossil fuels contributes to international terrorism.

Sanders referenced a 2015 report from the CIA that found that climate change contributed to problems of poverty, environmental degradation, and the weakening of political institutions.

A press release regarding the report reads:

"The report finds that climate change is a security risk, Pentagon officials said, because it degrades living conditions, human security, and the ability of governments to meet the basic needs of their populations. Communities and states that already are fragile and have limited resources are significantly more vulnerable to disruption and far less likely to respond effectively and be resilient to new challenges, they added."

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Another study published earlier this year in the Proceedings of the National Academy of Science explained how climate change in the Middle East contributed to the extreme drought in Syria, leading to a climate of political instability that was a factor in the 2011 uprising known as the Arab Spring.

"The link between climate change and conflict has been debated for years," the New York Times reported. "A working group of the Intergovernmental Panel on Climate Change wrote in 2014 that there was 'justifiable common concern' that climate change increased the risk of armed conflict in certain circumstances, but said it was unclear how strong the effect was."