Biden warns climate change is 'greatest threat' to US security: 'This is not a joke'

The president said he would speak to key European allies about a unified approach to combating climate change

President Biden warned military servicemembers Wednesday that top Pentagon officials consider climate change to be the "greatest threat" to America’s national security in the coming years.

"When I went over to the tank in the Pentagon when I was first was elected vice president with President Obama, the military sat us down and let us know what the greatest threats facing America were, the greatest physical threats," he said. "This is not a joke. You know what the Joint Chiefs told us the greatest physical threat facing America was? Global warming. 

"There will be significant population movements, fights over land, millions of people leaving places because they’re literally sinking below the sea in Indonesia, because of the fights over what is arable land anymore," he added.

Biden issued the warning during a speech to Air Force personnel stationed in the United Kingdom. The president will participate in meetings with G-7 and NATO leaders this month during his first overseas trip since entering the White House. 

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He made the declaration amid pressure from Republican lawmakers regarding his policy toward Russia in the wake of ransomware attacks that targeted key U.S. infrastructure, including his administration’s decision to waive sanctions on the Russia-backed Nord Stream 2 pipeline.

The president said he would speak to key European allies about a unified approach to combating climate change, which he has identified as a priority for his administration.

"We must all commit to an ambitious climate action if we’re going to prevent the worst impacts of climate change, limiting global warming to no more than 1.5 degrees Celsius and lead the global transition in clean energy technology," Biden said.

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The U.S. formally rejoined the Paris Climate Agreement in February following Biden’s day-one executive order. The order reversed a Trump-era decision to withdraw from the accord.

Biden has suggested that climate change poses a threat to U.S. military security on multiple occasions. In February, he noted that he had directed the Pentagon to reimagine the country’s strategy for dealing with the impact of climate change.

At the time, Biden said global warming was "already costing us billions in impacts on our bases and our national security."