According to the Department of Defense, climate change has already presented a significant challenge to U.S. national security. 
 
A Pentagon report on climate change, released earlier this month, was quoted by Defense Secretary Lloyd Austin saying that "to keep the country safe, we must address the existential threat of climate change."

According to the landmark report, climate-security threats include:

Rising temperatures.
Extreme weather events are becoming more frequent and intense.
An increase in anthropogenic climate change will compound existing risks and present security risks in the future.

Austin pointed out that “I retired as Deputy Chief of Naval Operations after serving over 30 years in the Navy. I managed service relationships with defense agencies across the federal government and coordinated global naval operations and strategic planning. Because of this position and my time as commander of the Southern Command of the U.S. Navy, I have been able to personally witness the effects of climate change on our neighbors, allies and enemies around the world.”

In an interview with the military's Southern Command commander, he recounted flying over Central American farms in 2019 during an arid year and 2020 during an extremely wet year. Increasingly extreme weather conditions and low agricultural yields for two years have led to the migration northward.

The consequences are also evident at home. East Central Florida has been experiencing flooding, rising sea levels and extreme heatwaves already this year, and this is just the beginning. 500 homes flooded in Orlo Vista because of Hurricane Irma in 2017, and residents were required to evacuate. The bases along Florida's coastal areas are also projected to surge 10 times more frequently than they did in 2016. By 2050, the state will have four times as many dangerously hot days, from 25 to 100 today.

The cost of these threats is high. A total of $1 billion was spent on extreme heat-related injuries by the military between 2008 and 2018. Climate change poses the fourth most significant threat to Patrick Space Force Base, according to the Air Force. Space exploration is rapidly expanding, but Kennedy Space Center and Cape Canaveral, Air Force Station, are located in coastal areas and are thus threatened by rising sea levels.

The science of climate change involves uncertainty, so planning for the future requires flexibility while incorporating mitigation and resilience measures. According to the Air Force, climate effective and cost-efficient mitigation and adaptation measures should be carefully designed based on long-term consequences.

In the United States, for far too long, we have ignored the effects of climate change on our outdated and inadequate infrastructure. It is already estimated that climate disasters amount to more than $16 billion in costs annually due to ignoring these issues.