In my public career, both in the Senate and at the Department of Defense, preparing for climate change was an important part of my work.

Climate science advanced rapidly over my decades in public service, my priorities remained the same: any actions to address climate change must protect America's economy, environment, and our national security. My views were always informed by science. As scientists reduced uncertainty about climate change over the last two decades, it became clear that the United States must implement policies to address the challenge -- because climate change is threatening our economy, the environment, and our national security.

"Climate change is threatening our economy, the environment, and our national security."

In 1997, the Senate passed the Byrd-Hagel Resolution, which laid out the conditions for Senate support of an international agreement on carbon emissions. Later that year, I led the Senate delegation to the Kyoto negotiations. In 2005, I authored the climate section of the Energy Policy Act, creating the Department of Energy Loan Guarantee Program and the international Clean Energy Ministerial meeting. In 2007, I led the effort to require a National Intelligence Assessment of the security impacts of climate change. As Secretary of Defense, I issued the Department's first Arctic Strategy in 2013, highlighting how the military would respond to melting ice and other challenges, as well as the Department's first Climate Adaptation Roadmap, detailing how to prepare for climate change. I supported the 2015 Paris Climate Agreement because it met the requirements of the Byrd-Hagel resolution, ensuring that all nations take measurable, reportable, and verifiable steps to reduce their emissions.

"As Secretary of Defense, I issued the Department's first Arctic Strategy in 2013, highlighting how the military would respond to melting ice and other challenges, as well as the Department's first Climate Adaptation Roadmap, detailing how to prepare for climate change."

Climate change is already affecting every sector and region of the U.S., as hundreds of top scientists from 13 federal agencies made clear in a report the White House itself released last year. The past five years were the warmest ever recorded. Without steep pollution reductions, climate change will risk tens of thousands of U.S. lives every year by the end of the century. Rising seas, along with increased storm surge and tidal flooding threaten $1 trillion of public infrastructure and private property currently built along U.S. coastlines. Since 2014,  the U.S. has experienced at least $400 billion in weather and climate disaster costs. Further, the hurricanes that slammed America's southern coasts, as well as historic wildfires in California, resulted in more American victims of severe weather juiced by climate change than ever before.

"Climate change is already affecting every sector and region of the U.S., as hundreds of top scientists from 13 federal agencies made clear in a report the White House itself released last year."

Dating back to the George H.W. Bush Administration in 1992, intelligence and national security professionals were telling us that climate change posed a direct threat to U.S. national security. This work has been informed by U.S. scientists telling us that a melting Arctic, more frequent droughts and floods, and extreme weather are all examples of the changing climate in the U.S. and the world. Changing weather patterns threaten our national security through its impacts on military infrastructure, disaster response, and the economy. If you put a map of places with high political instability today over a map of places with high climate vulnerability, the two would be nearly identical. The American Security Project, an organization of retired flag officers who spent their careers in uniform and other leaders, calls climate change a "ring road" issue, meaning that climate change will worsen other threats facing the nation. "It will change disease vectors. It will drive migration. These changes, in turn, could affect state stability and harm global security," the ASP reported.

"Dating back to the George H.W. Bush Administration in 1992, intelligence and national security professionals were telling us that climate change posed a direct threat to U.S. national security. Since 2014,  the U.S. has experienced at least $400 billion in weather and climate disaster costs."

We don't need to wait for more sophisticated climate models to project the security consequences of climate change. The impacts of climate change are clearly evident today.

Recent years' extreme weather has seriously affected our military readiness. Hurricane Florence decimated Camp Lejeune, and caused damage to Fort Bragg and military installations across North Carolina. A few weeks later, Hurricane Michael leveled Tyndall Air Force Base on Florida's Panhandle, causing damage to 17 F-22 stealth fighters and major structural damage throughout the base. Floods in my home state of Nebraska severely damaged the runway and infrastructure at Offutt Air Force Base, home of U.S. Strategic Command. As a Nebraskan, spring floods surprise no one back home. However, these floods were far more extreme than anything we'd seen. We also saw record-setting flooding across the Midwest, and specifically along the Missouri, Platte, and Elkhorn rivers. Estimated costs of these disasters to the military were significant. The Marines requested $3.6 billion to rebuild their North Carolina operations, while the Air Force requested an initial $5 billion for Tyndall and Offutt.

"Changing weather patterns threaten our national security through its impacts on military infrastructure, disaster response, and the economy. The Marines requested $3.6 billion to rebuild their North Carolina operations..."

While the bases may rebuild over time, the loss of training and readiness cannot be recovered. In a letter to the Secretary of the Navy, General Neller, Commandant of the Marine Corps, wrote that because of the damage from the storms, "The combat readiness of Marine Expeditionary Force -- 1/3 the combat power of the Marine Corps -- is degraded and will continue to degrade."

The weight of scientific evidence and present-day realities is undeniable: climate change is a real and present threat to our national security, which will get worse until we get serious about addressing it.