US President Donald Trump relies far more than his recent predecessors on advisers with a military background, but his apparent disregard for climate science is at odds with the US military's consensus on the risks of climate change to security.
Over the last decade, the US military and intelligence officials have developed a broad agreement about the security threats that climate change presents, in part by threatening to cause natural disasters in densely populated coastal areas, damage American military bases worldwide and open up new natural resources to global competition.
In his comments on Thursday (local time) announcing he had decided to pull out of the Paris climate agreement, Trump focused on economic issues, arguing that abandoning the deal would save manufacturing and mining jobs that he views as crucial to the US economy.
In 2012, Trump tweeted that climate change was a hoax perpetrated by China, and this week his aides repeatedly declined to answer directly when asked if he believes in the phenomenon. When asked at a Friday briefing if Trump believes in climate change, his spokesman Sean Spicer said he had not spoken to the president about it.
In seemingly doubting the existence of climate change, Trump is at odds with the military he leads.
"We're living in it, we are operational," said Ray Toll, a retired US Navy captain who conducted a pilot project with former President Barack Obama's White House to examine the regional challenges presented by climate change.
"If you're changing the dynamics, changing the environment, changing the conditions, it's going to have all kinds of impacts on the way you launch weapons, the way you deploy people."
Asked about the national security role of climate change in an interview with CBS' Face the Nation on Saturday, US Defense Secretary Jim Mattis demurred, saying the Paris agreement is "not inside my portfolio" and that the Pentagon deals with aspects of a warming climate.
But in written testimony to the Senate Armed Services Committee after his confirmation hearing in January, Mattis wrote that "climate change can be a driver of instability" and "a challenge that requires a broader, whole-of-government response." The testimony was published by ProPublica in March.
MANY RISKS
His answers reflected, in part, a broad consensus laid out in a September 2016 memo prepared by the National Intelligence Council, which advises US intelligence agencies, and said that climate change presents risks to stability, human health, and food supplies.
That followed an assessment in the Pentagon's 2010 Quadrennial Defense Review Report that said climate change "may act as an accelerant of instability or conflict."
In Syria, a drought about a decade ago was one link in a long chain of events that helped result in the civil war there, said David Titley, a retired US Navy rear admiral who started the Navy's Task Force on Climate Change in 2009.
That war has contributed to the rise of Islamic State, an ultra-hardline militant group that has planned and carried out attacks against the West, and which Trump has vowed to destroy.
In 2016, the Union of Concerned Scientists, a non-profit science advocacy group, assessed that 128 coastal military installations in the United States would be threatened by a three-foot increase in sea levels.
One of the most vulnerable US installations is the US Naval Support Facility at the Diego Garcia atoll in the Indian Ocean, which acts as a logistics hub for US forces in the Middle East and has an average elevation of four feet above sea level.
"We have used that island for every significant military operation in Southwest Asia," said Titley, who now teaches at Pennsylvania State University.
The US military also faces risks less than a day's drive from the White House. The main road to the US Naval Station in Norfolk, Virginia, the world's largest naval base, experiences chronic flooding, and electric and water utilities supporting the base are threatened every time the waters rise.
