Charges of Russian meddling in the 2016 election, cybersecurity and terrorism are topics that have recently dominated the national security conversation.

But according to Richard Clarke, it's climate change that poses an imminent threat to our nation's shores.

Clarke is the former U.S. national security adviser who gained notoriety after criticizing the George W. Bush administration for the war in Iraq, saying Bush is guilty of war crimes.

He was in San Francisco last week for the 2017 RSA Conference -- the world's leading conference on cybersecurity -- but he had rising seas on his mind.

[audio src="http://www.kqed.org/.stream/anon/radio/tcr/2017/02/2017-02-17c-tcr.mp3" Image="https://ww2.kqed.org/news/wp-content/uploads/sites/10/2017/02/SCraig_Sealevelrise-800x531.jpg" Title="Climate Change Is California's Biggest Threat, Says Former National Security Adviser" program="The California Report"]

"Californians and anyone living on the coast need to be worried about sea level rise, which can happen much faster than we anticipated," he said.

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Clarke is concerned about chaos that will occur not just in California, but around the globe from rising seas that could displace millions of people.

He noted that the drought in Syria contributed to that country's refugee crisis, and pointed to the situation as an example of how a changing climate can lead to political instability.

"If sea level rise happens to the extent it could ... when you have millions of people who are on the move ... that usually results, as we've seen in the Syrian refugee crisis, in political disruption and security problems."

Former U.S. National Security Adviser Richard Clarke. (Alex Wong/Getty Images)

Clarke also stressed that the United States' federal budget will be hit hard.

"You are going to be spending huge amounts of money on flood control and reconstruction of infrastructure," he said.

"So much so, that you won’t continue to have money to continue to afford a large defense establishment like we have now."

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