I recently followed a drone through the ruined Syrian city of Aleppo, courtesy of YouTube. The destruction was sobering, to say the least. The camera glided by exploded apartment buildings and streets piled with rubble, block after city block. The political situation in Syria is contemptible, the impact of war on human lives horrendously tragic, all silently conveyed in the aftermath captured on video. It also captured something more subtle, something that could easily go unnoticed: Aleppo was built almost entirely of concrete. Concrete dominated every shot. That observation might seem strange, but bear with me.
Of all the multitudinous things we humans manufacture, concrete is among the most common. To make it, we dynamite limestone out of the Earth's crust and cook it at 2,700 degrees Fahrenheit. This produces cement, the adhesive component of concrete. Heat changes limestone's molecular structure, making it reactive with water, so a bag of gray powder and some aggregate, like rock or sand, can be conveniently turned back into a strong solid of any shape with water from a garden hose.
The amount of fossil fuel required to make cement is astonishing: Producing 1 ton of concrete, about a cubic yard, uses the equivalent of 400 pounds of coal. The concrete industry accounts for 5% of the world's greenhouse gas emissions. When I see all the concrete used to build Aleppo, I think of what has been released into the air to produce it.
From numerous studies, scientists know that climate destablization — from the burning of fossil fuels in places such as the U.S., China and India — is causing drought in the Middle East. In fact, for the last decade or so, Syria and the eastern Mediterranean have been in the midst of their worst drought in nine centuries. The effect has been to turn Syria's once-productive soil into hard-baked clay. Since 2008, food prices in Syria have increased an average of 26% a year. A million farmers have lost their livelihoods. Desperate young men from the countryside have crowded into the cities, seeking a means to survive.
In 2011, Syrians in Aleppo took to the streets. Discontent, hunger, unemployment and corruption fed the civil war and the ranks of extremists, including Islamic State. In Syria, a change in climate has disintegrated a society in a handful of years.
Climate change as an underlying cause of social conflict is rarely front and center in the news, but it has been documented by a variety of experts. In a letter released in September, U.S. military leaders and members of the national security community called climate change what it is: a "significant and direct risk to the U.S. homeland." We mistakenly think of such threats as coming from outside our borders. Aleppo shows us that they will also come from within.
Already, extreme heat, drought and floods in the United States have grown increasingly common, intense and chaotic. In the summer of 2015, rainfall in normally arid Texas was measured in feet, not inches. Meanwhile, humid subtropical states such as Alabama have been experiencing extreme drought. In the short term, climate destabilization creates whiplash for farmers trying to plan. In the long term, the situation is much more serious: Climate models project mega-droughts that will disrupt agriculture across America in the coming decades.
In Aleppo, the blasted concrete walls are not just an outcome of conflict. They are also, unexpectedly, part of the cause. And however remote and disconnected from our lives places and conflicts like Aleppo seem, the physical rules and conditions that create tragedy there also apply here. The world's troubled places aren't outliers in human history: They're harbingers. They underscore a lesson history keeps trying to teach us: A deep, unshakable pursuit of sustainability is essential for lasting peace and prosperity. Anything less and humans can expect a growing litany of miseries.
Sustainability, if not easy, is achievable — even when it comes to concrete. The technology already exists to make cement without emitting any greenhouse gases. Scientists and engineers actually learned the technique from coral, a sea animal that takes in minerals and carbon dioxide from seawater to produce a calcium carbonate exoskeleton — coral reefs.
The human version works by reacting the CO2 in industrial flue stacks with calcium-rich water, resulting in powdered limestone — tons of it — no mining, no heating and so no greenhouse gases. In fact, cement produced this way is carbon negative: It cleans our atmosphere of greenhouse gases (the CO2 in the flues) as a byproduct of the manufacturing process. The commercialized coral-inspired cement-making process would be more price competitive if there were an economic cost to dumping carbon dioxide in the atmosphere. Instead, most CO2 emitters pay nothing for their socially destructive practices. The means to make cement in an economical and ecologically healthy way seems extraordinary, but all around us nature empirically demonstrates the prospect of both a sustainable and productive human-built world.
Natural systems and human events are deeply interconnected, and if you look closely, very often the issues that lead to social conflict hinge on the use of resources and the misuse of the environment. The ruins of Aleppo graphically illustrate our species' current misguided path. But properly understood, they are also an opportunity for clarity, redirection and hope.
Sam Stier is director of the Center for Learning With Nature (www.LearningWithNature.org) and teaches science and sustainable design at Otis College of Art and Design.