By Jon Gensler

According to the Obama administration’s new National Climate Assessment, climate change is already impacting communities in every corner of the country, with an increasing frequency and severity of extreme weather events — storms, floods and droughts — and rising sea levels destabilizing the everyday lives of Americans.

Worse, the impacts of these changes are accelerating. They are affecting communities around the world. The Pentagon’s most recent quadrennial defense review warns that “climate change may increase the frequency, scale and complexity of future missions.”

Some of the least stable states in the world will face changing weather patterns that reduce arable land and fresh-water supplies, in turn driving mass-migration, provoking resource conflicts and fostering global health threats.

As a former Army officer, I have seen firsthand how “climate disruption” puts more of my fellow soldiers at greater risk. Both the creeping effects of climate change, producing gradual shifts over time, as well as the increasing frequency and severity of natural disasters pose unique threats to global security.

Urban poverty is a major driver of terrorism, and climate-based migrations from disappearing coastal communities are likely to cause huge influxes in city populations around the world over the coming decades. Bangladesh, one of the most densely populated states in the world, could see up to 18 million people displaced by 2050.

Competition for resources has been a fundamental driver in human conflict for centuries. States in sub-Saharan Africa, the Middle East and Central Asia have all already experienced varying levels of conflict and diplomatic tensions over access to freshwater resources. Moreover, rising saltwater levels in irrigation-dependent regions like the Mekong Delta in Vietnam threaten the food supplies of millions of people.

Global health is at risk, too. Rising temperatures are expanding the range of deadly diseases once confined to relatively small subtropical geographic areas. Instances of Dengue, a mosquito-borne virus with flu-like symptoms, have been on the rise in Florida and Texas. Alarmingly, the increase in instances of Dengue in the United States have not come from travelers returning from abroad. Instead, the disease’s indigenous zone is expanding due to increased heat and rainfall.

Ultimately, the disenfranchised and destitute are more likely to resort to violence as a means of finding income and creating purpose. High-profile security threats like the situations in Mali, Yemen and Somalia all serve as clear examples of extremists gaining footholds in volatile societies. A central government that cannot provide for the basic needs of its people will only be more impotent in the face of climate-based challenges.

Yet these gradual shifts in weather patterns — while incontrovertibly causing serious change over time — are not even the most immediate threat to international stability. Natural disasters, increasing in both number and severity, are posing a greater risk at home and abroad.

Whether after Typhoon Haiyan in the Philippines or New York City following superstorm Sandy, helping those in need after tragedy strikes is a responsible way to uphold America’s moral leadership and build cooperation between nations. However, in a budget-constrained environment, any increase in the number of disasters is certain to stretch thin our military’s resources and divert attention from its primary mission.

Every humanitarian challenge that goes unanswered by the United States presents an opportunity for extremist groups to curry favor with communities; providing relief is a classic strategy of those seeking to implement radical social agendas. Groups in Syria, Pakistan and Myanmar have all endeared themselves to local populations via providing supplies, protection, and social structure at the cost of assuming moral authority.

The threats to our collective security are as abundant as they are clear. While civilian debate on climate change drags on, the U.S. military has taken the lead in preparing to both adapt and react to climate-based challenges. Our security professionals understand that continued dependence on fossil fuels and willful scientific ignorance are not an option for a nation with major clout on the world stage.

This century must be one of innovation, both in technology and policy. The National Climate Assessment is clear: There are no winners in a worst-case scenario, because climate change will impact us all. We need to take more aggressive action, and the time for American global leadership by way of comprehensive climate legislation is now.

This is the only hope we have of staving off the worst impacts of climate change. If we fail to take immediate action, we risk destabilizing the world to a point where it cannot sustain the peace and democracy we worked so hard to build. And that is the most serious long-term security threat we face.

JON GENSLER, a former Army officer, is a fellow with the Truman National Security Project and is a consultant with Cambridge Leadership Associates. This column originally appeared at Defense One. Contact: jgensler@cambridge-leadership.com.