David Titley, a retired rear admiral, is the founding director of the Center for Solutions to Weather and Climate Risk at Penn State University and a senior adjunct fellow at the Center for New American Security. He served as Oceanographer of the U.S. Navy from 2009 to 2012. He is on Twitter.

Updated September 2, 2015, 3:31 AM
The New York Times 

Climate change will become one of the principal threats to our national security. The likelihood of climate-related events happening is very high, and we have already seen that the direct and indirect consequences are severe.

Climate change will likely trigger large-scale instability as heat, floods, drought, ocean acidification and rising sea levels disrupt local and global food markets, fresh water sources, and the very existence of low-lying nation states. In 2010, droughts and heat waves reduced wheat harvests in Russia, Ukraine and Australia. This forced a rapid rise in wheat prices that, which exacerbated pre-existing grievances about poor governance to set off the Arab Spring, with security consequences we are still dealing with today. As Anne-Marie Slaughter stated in 2013, “The consequences of climate change are stressors that can ignite a volatile mix of underlying causes that erupt into revolution.”

The Arctic is a harbinger of the opportunities and security threats embedded in climate change. The receding Arctic ice is exposing Europe’s northern frontier, previously locked in ice. The demand on Coast Guard and constabulary forces increases with the expansion of trade routes, tourism, fisheries, and resource exploitation. And Russia’s increased Arctic military capabilities creates new threats, as its intentions remain opaque.

Rising sea levels, more intense floods, rising temperatures and fires can even threaten our troops’ safety and readiness. If the base is flooded, if it is too hot and humid for strenuous physical work, or if the air quality is degraded by wildfires, military personnel cannot train hard enough or realistically enough to prevail on the battlefield.

Climate change makes existing security threats worse. Failing to think through these scenarios is nothing less than a failure of imagination.