The first time I truly understood concrete’s climate impact, I was crouched inside a half-finished building in Morocco, my hand pressed against a wall that wasn’t made of concrete at all. It was earth—simple clay, sand, and lime compressed into a material so solid that it had withstood centuries of earthquakes, desert storms, and human occupation.
“This building technique is over a thousand years old,” explained Hassan, the master builder who’d been showing me around various construction sites in Marrakech. “But to most architects trained today, it might as well be alien technology.”
He ran his hand along the rammed earth wall, which glowed a warm amber in the late afternoon light. “Your modern concrete buildings will crumble long before these walls fail,” he said with the quiet confidence of someone who has witnessed the vindication of traditional wisdom. “And they’ll poison your atmosphere in the process.”
He wasn’t exaggerating about concrete’s environmental impact. The hard truth is that concrete—that seemingly innocuous gray stuff that forms our modern world—has a carbon footprint that would make a coal baron blush. Cement production alone (cement being the binding ingredient in concrete) accounts for about 8% of global carbon emissions. If the cement industry were a country, it would rank third in emissions behind only China and the United States.
The problem lies primarily in the production of Portland cement, which requires heating limestone to about 1,450°C—an enormously energy-intensive process that also triggers a chemical reaction releasing carbon dioxide from the limestone itself. It’s a double climate whammy. And with global concrete use tripling over the past 20 years, reaching a staggering 30 billion tons annually, we simply can’t address climate change without tackling concrete.
Yet most climate conversations completely overlook it. We obsess about electric cars and renewable energy (both critically important, of course) while ignoring the massive gray elephant in the room. I’ve sat through countless climate conferences where construction materials weren’t mentioned once, despite their enormous carbon footprint.
My own wake-up call came about five years ago during a research trip to that building site in Morocco. I’d gone there to write about something completely different—traditional water management systems—but found myself increasingly distracted by the buildings themselves. While new developments used concrete almost exclusively, the centuries-old structures that had drawn tourists and architects from around the world used materials with a fraction of the environmental impact: rammed earth, lime, stone, wood, and brick made with simple firing techniques.
That experience sent me down a rabbit hole of research into alternatives to conventional concrete. What I discovered was simultaneously hopeful and frustrating—a wealth of low-carbon building methods already exist, some ancient and some cutting-edge, yet they remain niche approaches in a construction industry resistant to change.
Let’s start with the traditional techniques that have stood the test of time—literally thousands of years in some cases. Rammed earth, the method I observed in Morocco, involves compacting slightly moistened subsoil (clay, sand, and gravel) mixed with small amounts of lime or other stabilizers into formwork. The resulting walls are solid, naturally insulating, and capable of supporting multi-story structures.
Modern adaptations have made this ancient technique even more effective. Stabilized rammed earth adds small amounts of cement (typically 5-10% compared to conventional concrete) to increase strength and water resistance. The environmental savings are enormous—up to 90% less carbon emissions than conventional concrete construction—while maintaining exceptional thermal mass that reduces heating and cooling needs throughout the building’s life.
I visited a recently completed rammed earth home in Devon last year, built by a couple who had no previous construction experience but had become obsessed with traditional building methods. The walls were 18 inches thick, a rich golden color with subtle horizontal striations showing where each layer had been compacted.
“Everyone told us we were mad to try this ourselves,” Sarah told me as she showed me around their beautiful, quiet home. “But the technique is fundamentally simple—it’s just soil, after all.” They’d sourced most of their material directly from the building site excavation, meaning virtually zero transportation emissions. The embodied carbon was approximately 25% of an equivalent conventional structure.
Another ancient technique enjoying a modest revival is cob—a mixture of clay-heavy soil, straw, and water that’s shaped by hand into monolithic walls. Unlike rammed earth, which creates a stone-like material, cob remains somewhat plastic during construction, allowing for organic, sculptural forms. It’s extraordinarily durable—Devon contains numerous 500-year-old cob cottages still in perfect condition—and has approximately one-tenth the embodied carbon of conventional construction.
“People assume these natural materials are fragile or primitive,” explained Martin, an architect specializing in traditional building techniques whom I interviewed for a feature last year. “But they’ve survived centuries of British weather. How many concrete buildings from the 1960s can say the same?”
He’s right about concrete’s often overstated durability. While it can theoretically last centuries under perfect conditions, in practice many concrete structures begin deteriorating within decades due to carbonation, freeze-thaw cycles, and corrosion of internal reinforcement. The Pantheon in Rome, built with Roman concrete nearly 2,000 years ago, has outlasted countless modern concrete structures because of fundamental differences in composition and technique.
Which brings us to another fascinating alternative—Roman concrete itself. Unlike modern Portland cement concrete, Roman concrete used lime combined with volcanic ash (pozzolanic material) that actually strengthens over time through a process of mineralization. Modern researchers have reverse-engineered similar mixtures that reduce emissions by 30-60% compared to conventional concrete while creating more durable structures.
I spoke with Dr. Elena Costa, a material scientist working on modern adaptations of Roman concrete, during a research trip to Italy. “The Romans weren’t trying to be sustainable,” she laughed as we examined samples in her lab. “They were just working with locally available materials in the most effective way they knew. But in doing so, they created something far more climate-friendly than what we use today.”
Her team has developed a limestone-calcined clay cement that mimics the properties of Roman concrete while being compatible with modern construction techniques. Early projects using this material have shown remarkable durability with approximately 40% lower carbon emissions.
Lime-based building techniques represent another traditional approach with significant climate benefits. Unlike Portland cement, which is fired at extremely high temperatures, lime is produced at lower temperatures (around 900°C compared to 1,450°C) and reabsorbs much of its production CO2 during curing through a process called carbonation. Lime mortars, plasters, and renders have been used for thousands of years and create breathable, naturally insulating structures.
My friend Jun (yes, the same one from my university days who could fix anything electronic) recently renovated his Victorian terrace house using exclusively lime-based materials. “The building surveyor thought I was mad,” he told me over dinner in his beautifully restored home. “He kept pushing for cement renders and gypsum plaster. But this house had stood for 140 years with lime; adding cement would have been like putting it in a plastic bag.””
The results speak for themselves. His home maintains perfect humidity levels without mechanical ventilation, the walls breathe moisture naturally, and the carbon footprint of his renovation was approximately one-third of a conventional approach. Plus, as he proudly demonstrated by taking a hammer to a small section of plaster (making me wince in the process), lime-based materials can be easily repaired or even fully recycled at end of life, unlike most cement-based products.
But traditional techniques are only part of the solution. Some of the most exciting developments in zero-carbon construction come from combining ancient wisdom with cutting-edge innovation. Hempcrete, for instance, mixes hemp hurds (the woody core of the plant) with lime to create a lightweight insulating material that actually sequesters carbon. Hemp grows quickly with minimal inputs, absorbing CO2 as it grows, while the lime binder continues absorbing carbon throughout the building’s life through carbonation.
I visited a hempcrete construction site in Somerset last summer, watching as builders mixed the hemp and lime in a conventional cement mixer before packing it into timber formwork around a structural wood frame. The material was lightweight enough that a single builder could carry a full tub up scaffolding.
“It’s basically the opposite of concrete environmentally,” explained the project manager, Ella. “Instead of emitting carbon, we’re locking it up in the walls. This small house will store about 20 tons of CO2 equivalent when complete.” Beyond the carbon benefits, hempcrete creates highly insulated, breathable walls that regulate humidity and temperature naturally, reducing operational energy needs.
Another bio-based material gaining traction is mycelium—essentially the root structure of fungi—which can be grown on agricultural waste to create building materials with minimal energy input. I’ve been following the work of a research team at Imperial College developing mycelium-based bricks and insulation panels that outperform many conventional materials while sequestering carbon and being fully biodegradable at end of life.
“We’re literally growing building materials instead of manufacturing them,” Dr. Shanika Amarasekara told me during a lab visit where I got to handle some of their experimental mycelium products. “The fungi do most of the work, consuming agricultural waste and transforming it into a structural material using minimal energy.”
While some of these alternatives sound like science fiction, others are hidden in plain sight. Cross-laminated timber (CLT) has revolutionized mid-rise construction in parts of Europe, allowing wood to replace concrete and steel in buildings up to 18 stories tall. Since trees absorb carbon as they grow, and that carbon remains stored in timber products, wooden buildings can be carbon-negative over their life cycle.
The Stadthaus in London, a nine-story apartment building constructed primarily from CLT, stored approximately 186 tons of carbon while avoiding 124 tons of emissions from concrete and steel construction. That’s equivalent to taking 120 cars off the road for a year—from a single building. The structure was assembled by four people in 27 days, compared to the estimated 72 weeks for an equivalent concrete building, demonstrating that sustainable materials can offer practical advantages beyond their environmental benefits.
But what about situations where we genuinely need concrete-like performance? That’s where some of the most innovative alternatives come in. Geopolymer concrete substitutes industrial byproducts like fly ash or ground granulated blast furnace slag for Portland cement, activated with alkaline solutions rather than through high-temperature firing. The resulting material can have similar or superior properties to conventional concrete with 40-80% lower carbon emissions.
I visited a geopolymer concrete facility in the Midlands last year, where they were manufacturing precast elements for infrastructure projects. “We’re taking waste products that would otherwise go to landfill and turning them into construction materials,” explained the operations manager as we watched massive bridge sections being cast. “The carbon footprint is a fraction of conventional concrete, but the performance is identical or better in most applications.”
Even more promising are carbonate-based materials that actively absorb CO2 during production. Several startups have developed processes that inject captured carbon dioxide into concrete mixtures, where it chemically binds with other ingredients to form calcium carbonates. This approach can reduce the carbon footprint of concrete by 5-30% while potentially improving strength.
The most advanced carbon-negative concretes go further, using specialized production processes that absorb more carbon than they emit. These materials remain relatively expensive and limited in availability, but they demonstrate that even the most challenging building material can be reimagined for a zero-carbon future.
With all these alternatives available, you might wonder why conventional concrete still dominates construction worldwide. The barriers are numerous but not insurmountable. Building codes and standards developed around Portland cement concrete can make it difficult to get approval for alternatives. The construction industry is notoriously conservative, with liability concerns driving reluctance to adopt new materials. And the economies of scale currently favor conventional concrete, making alternatives more expensive in many markets.
But these dynamics are shifting. As carbon pricing becomes more common and climate regulations tighten, the true cost of conventional concrete will increasingly be reflected in its price. Innovative companies are scaling up production of alternatives, driving down costs through improved manufacturing processes. And a new generation of architects and builders is actively seeking out low-carbon materials, creating market demand that drives further innovation.
I spoke with Rowan, a young architect who specializes in low-carbon design, about this shift. “Five years ago, suggesting rammed earth or CLT for a major project would have been career suicide,” she told me over coffee near her London office. “Now clients are specifically asking for these materials because of their environmental benefits and aesthetic appeal. The conversation has completely changed.”
She showed me designs for her latest project—a community center using a combination of rammed earth, timber, and straw bale construction that would sequester approximately 40 tons of carbon rather than emitting hundreds of tons through conventional methods. What struck me most was how normal this approach is becoming in certain sectors of the industry.
My own experiments with alternative building materials have been more modest. Last summer, I helped a friend build a garden studio using light earth technique—essentially straw coated with clay slip packed into a timber frame. We sourced clay from a nearby construction excavation (they were happy to give it away rather than pay for disposal) and straw from a local organic farm. The total carbon footprint was negligible, and the resulting space stays cool in summer and warm in winter with minimal heating.
The experience gave me a visceral understanding of how differently we could approach construction. There was no noisy cement mixer, no dust-masked workers, no pallets of bagged materials. Just earth, straw, water, and wood, combined with human labor that felt satisfying rather than exhausting. The studio has weathered two British winters beautifully so far, with no signs of the deterioration many people warned us about.
Of course, not everyone can or should build their own structures from scratch. But the principles and materials we used are entirely applicable to mainstream construction. The barriers aren’t primarily technical—they’re cultural, regulatory, and economic. Changing these systems requires multiple approaches: regulatory reforms that account for carbon emissions in building codes, research funding for alternative materials, education programs that teach traditional techniques alongside modern methods, and most importantly, continued demonstration that these alternatives work.
Hassan, that master builder in Morocco, told me something I think about often. “Modern architects design for photographs,” he said as we walked through a rammed earth building that had stood for centuries. “Traditional builders designed for generations.” The contrast captures something essential about our current approach to construction—its emphasis on immediate visual impact over longevity and environmental compatibility.
But I’m increasingly hopeful that we’re returning to a more balanced approach, one that combines the best of traditional wisdom with modern innovation. Zero-carbon buildings aren’t a futuristic fantasy—they’re already being built using techniques both ancient and cutting-edge. The question isn’t whether we can construct buildings without massive carbon emissions, but whether we have the wisdom and will to make this approach the new normal.
As I run my hand along the rammed earth wall of my friend’s garden studio, feeling its subtle texture and steady cool temperature even on a hot day, I’m reminded of that moment in Morocco years ago. The solutions to many of our most pressing environmental challenges already exist—sometimes hidden in plain sight, sometimes buried in ancient wisdom, and sometimes emerging from laboratories at the cutting edge of material science. Our task is to recognize them, improve them, and implement them at the scale our climate crisis demands.
