On January 27, newly-installed Secretary of Defense Lloyd Austin — having already made history as the first Black American appointed to the role — broke new ground for the Department of Defense. He declared that under his leadership, the department would treat climate change as a national security priority. “There is little about what the Department does to defend the American people that is not affected by climate change,” Austin argued. “It is a national security issue, and we must treat it as such.” It’s a very welcome step.

In a piece soon to be published in the American Defense Policy journal, we lay out a number of direct effects that a rapidly changing climate can have on security and conflict, as well as on the wider dynamics of American leadership of the international order.

Climate’s direct effects

The most immediate effect of climate change will be on internal conflict. Careful modeling suggests that changing climate patterns could drive an up to 50% increase in conflict in sub-Saharan Africa alone. This would result in several hundred thousand additional battle deaths, and the displacement of millions. And the patterns of war tell us that the effects of this will not be limited to the individual countries affected, but will spread both within Africa and beyond by the vectors of transnational terrorism and by mass migration.

Perhaps the most systematic, though not the most immediate, security consequences from a warming climate will come from sea-level rise. This will have several major effects. We are likely to see substantial migration from low-level island states, whose populations may migrate to coastal areas in Southeast Asia, with destabilizing effects. Sea-level rise is already putting economic pressure on important states in the coastal areas of the Indian Ocean, notably Bangladesh and Myanmar — both of which have large populations and large parts of their agricultural land in low-lying areas heavily exposed to rising sea levels. Myanmar, of course, plays a highly consequential role in Asian security politics, given its location between India and China, and its potential to serve as an alternative route for China into the Indian Ocean, bypassing the Malacca Straits.

Sea-level rise is very likely to directly affect the physical survival of several small island states. This is a security risk in its own right for those countries, but could also have wider implications, especially in the Western Pacific where U.S. naval installations and U.S. naval defense is highly dependent on a series of small island bases. This is already a topic of concern for U.S. Indo-Pacific Command leadership. And beyond the simple rise of sea levels, as the seas continue to warm, the resulting cyclones and hurricanes will be fed more energy from the warmer surfaces, making them more destructive in an absolute sense but also more destructive because these storms will drive surges of higher sea levels farther and farther inland — creating greater human misery, destruction, and economic stress. These intersecting climate effects will be devastating, with obvious security implications.

The bigger picture

There are also geopolitical implications. Two countries whose posture matters a great deal to both American and international security are Saudi Arabia and Russia — the former a putative U.S. security partner, albeit a troubled one, the latter a U.S. adversary. Both rely immensely on the sale of fossil fuels for their GDP and for state income. Saudi Arabia, for its part, has begun to think through what it means for it as a society that we are likely to see a transition away from fossil fuel consumption over the next 20 years — but has not yet done much to act on this. Russia, to be sure, has not. How these two countries cope with that change will likely have substantial implications for the stability and security of their regions and, in the case of Russia, for international security as a whole. We have only begun to think through this potentially challenging issue.

A very different question is India, an indispensable partner to the United States in the management of the Indo-Pacific region. India has over 300 million people who have little or no access to modern energy. As a democratic society, they have no choice but to attempt to industrialize to provide greater access to energy for their poor. But should India industrialize through the same carbon-intensive pathways as both the West and of China, then we will likely be locking in at least 4 degrees of temperature rise globally; an intolerable risk.

A fourth, and already consequential impact of changing weather patterns, is in the Arctic. Already warmer temperatures and the attendant melt of sea-ice is changing the patterns of flow across a once-frozen north. The Arctic is now providing new routes for trade during the summer months and could soon see year-round travel with ice-hardened ships and convoys of container ships. Certainly within 20 years, the northern sea route will open up a new shipping lane from the major container ports on China’s eastern shore to the markets of the eastern United States and across the Atlantic to Europe. Russia’s Navy is once again focused on the Barents Sea route into the North Atlantic, and U.S. submarines are once again patrolling the Norwegian Sea. The implications of all this are wide-ranging.

Where this leaves Washington

In all of the above — in its economic effects, as well as its effects on development, conflict, and geopolitics — climate change rebounds to the question of the effects on American leadership.

There are several challenges now to American leadership. Much of the security community is seized with these, most of all the challenge posed by the rise of China as an economic and increasingly a strategic actor. But the security community has not yet adequately seized the implications of climate change for American leadership. This has two essential dimensions. First, more fully understanding and preparing for the impacts laid out above: From increased conflict and migration to sea-level rise to changing patterns of stability and instability in great-power relations, climate change will affect multiple dimensions of international security in a direct sense. But there’s also a second, consequential feature of the issue.

Much of the world, including core American allies, treat climate change as a top-tier issue, one requiring seriousness of purpose and extensive global cooperation. If the U.S. fails to lead the world on mitigating climate change and on preparing to adapt to the consequences of the changes already baked into natural systems, this will contribute to the already diminishing confidence in American standing and leadership. The consequences of this would reverberate across every aspect of the American alliance dynamic, to include America’s viability as a leader of the international order. We welcome the initial steps taken by President Biden to reverse this dynamic — from rejoining the Paris Climate Accord to appointing the special envoy for climate change — and encouraging Secretary Austin to make climate issues central to national security planning.