Opponents to action often present the challenges of climate change as if they are the sole concern of "granola-crunching tree huggers". While it may be convenient, from a rhetorical perspective, for climate change deniers to caricature concern over the climate change threat in this manner, it is not very accurate at all. In reality, the national security community—hardly a bunch of environmental extremists—are among the communities most concerned about the potential impacts of projected future climate changes.
We have already seen that climate change could threaten food security, water security and health security. As there has often been the fierce competition for limited resources—be it food, water, land, etc.—it is reasonable to draw the conclusion that climate change may challenge national security. In fact, that is the conclusion of the U.S. Military. You can hear Dr. David Titley (formerly a Rear Admiral, the Navy's official oceanographer, and most recently a Professor of Practice at Penn State University and Director of the Center for Solutions to Weather and Climate Risk) discussing the potential national security threats of projected future climate change in this video:
Video: TED Talk - "How the Military Fights Climate Change" (7:41)
You can also find a thorough discussion of the potential national security threats of climate change in this report, The Age of Consequences: The Foreign Policy and National Security Implications of Global Climate Change, published by the Center for Strategic International Studies, and co-authored by leading national security experts including former CIA director James Woolsey. There is also a documentary of the same name looking at climate change and national security.
One recurring theme in discussions of U.S. national security impacts is the potential military implications of retreating Arctic sea ice. In recent years, the mythical "Northwest Passage" has finally opened up on a semi-regular basis. That is to say, it is now possible, over part of the year, for ships and submarines to travel unimpeded from the Labrador sea through the Arctic ocean, into the Pacific ocean. As the trajectory of sea ice retreat continues and the open channels widen and deepen, it will likely be possible for large military vessels (ships and submarines) to make this route. That would have deep implications for U.S. national security. Suddenly, the U.S. would need to defend a new (Arctic) coast line against potential invasion and military attack.
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Other scenarios involve the idea that increased conflict between nations and cultures may arise from so-called environmental refugeeism—people fleeing regions no longer fit for habitation for other currently occupied regions, thereby increasing the competition for resources. As parts of Sub-Saharan Africa, such as Senegal, become too dry and inhospitable for subsistence agriculture, for example, there may be a flood of human refugees fleeing this environment to the less arid south, e.g., to Ghana (indeed, there is evidence this is already happening). Another scenario is that the extremely large populations of interior Nigeria, driven by drying conditions, flee for the mega-city of Lagos to the south, where there is heightened competition for food and water resources. Adding to the incendiary mix is the skirmishes that might break out among groups and individuals fighting over the last remains of the disappearing oil reserves of the Niger River Delta, and the cronyism and political corruption that may ensue. Consider also the impact of an increasingly dry Middle East. Author Daniel Hillel has argued in Rivers of Eden that it is the competition for scarce water resources over the years that has driven much of the Middle East conflict. Imagine adding further fuel to the fire as water resources continue to disappear. New York Time's columnist (and Nobel Prize winner in economics) Paul Krugman has argued that climate change-related stresses on food supply may have had a role in recent unrest and uprisings in the region, such as that recently witnessed in Egypt. A more recent article on water supply can be found here. Could that be a sign of things to come?
The worst-case scenarios that researchers have envisioned are not entirely unlike the dystopian futures portrayed in 1970s and 1980s apocalyptic films such as Soylent Green and Mad Max.