On Nov. 16, The Economist delivered profoundly sobering news in its cover story, “What they don’t tell you about climate change”: Carbon dioxide reduction will be insufficient to combat global warming. This assertion takes into account not only actual greenhouse gas (GHG) emissions but also aspirational climate targets—such as the Paris climate accord. According to The Economist, “in any realistic scenario, emissions cannot be cut fast enough to keep the total stock of GHG sufficiently small to limit the rise in temperature successfully.”
Attaining environmentally responsible climate targets must also require the active removal of carbon dioxide from the atmosphere. The amount is staggering: according to Intergovernmental Panel on Climate Change (IPCC), 810 billion metric tonnes (approximately 892 billion tons) of the gas would need to be removed by 2100 to maintain a 2 C target temperature increase. That’s the amount of carbon dioxide the world currently produces in two decades.
Carbon reduction technologies exist, but they are generally expensive, time-intensive to adopt, and not widely implemented. Some industries and power-generation facilities practice carbon capture and storage, sequestering the carbon dioxide they produce underground. Other strategies include transitioning more aggressively to renewable energy, improving agricultural practices, planting more trees, or—more controversially—geoengineering proposals such as dispersing large quantities of sulfur within the stratosphere to reflect more sunlight into space.
One application that is conspicuously absent from the Economist article is building construction. Presumably, this omission is due to the fact that individual edifices are considered too small to be consequential—yet collectively, buildings consume nearly half of the Earth’s resources. Construction-related carbon dioxide-reduction technologies offer many compelling advantages, not the least of which is transforming one of the most environmentally detrimental sectors into one that is more aligned with IPCC objectives.
Several manufacturers have targeted concrete as a potential vehicle for carbon sequestration. Because cement production comprises 5 percent or more of global carbon dioxide emissions—a fact due both to cement’s high processing requirements and significant production volume—reducing its environmental impact is an obvious first step. One opportunity is to store carbon dioxide in calcium carbonate-based cementitious substances. Los Gatos, Ca.–based Blue Planet harnesses waste gas from a variety of industries and sequesters it within a kind of synthetic limestone. This carbonate material consists of waste rock particles coated with calcium carbonate, 44 percent of which is the diverted carbon dioxide. The company has developed several building-related products based on this technology including aggregate, sack concrete, titanium oxide replacement, and light-reflective roofing granules and pigments.
Blue Planet joins Nova Scotia-based CarbonCure, New Jersey-based Solidia Technologies, Australia-based Mineral Carbonation International, and California peer Calera in the pursuit of carbon-accumulating concrete. But more work must be done before the cementitious materials contribute measurably towards the 2 C target. First, the volume of stored carbon dioxide must be increased significantly. For example, a single concrete block made by CarbonCure exhibits only 5 percent reduction in carbon footprint, according to the MIT Technology Review. Second, the real emissions culprit of concrete, Portland cement, continues to demand an exorbitant amoutn of energy. Combining carbon-sequestering limestone aggregate with fly ash in lieu of some, if not all, of the required Portland cement would further improve concrete’s environmental performance.
Courtesy Blue Planet
Pouring materials at San Francisco Airport.
Another material with carbon dioxide-limiting potential is plastic. Petroleum-derived polymers exhibit a carbon footprint of approximately 6 kilograms of carbon dioxide per kilogram of finished material (approximately 13 pounds per pound). Three hundred million tons of plastic produced annually thus translates to 1.8 billion tons of carbon dioxide. Although the level of worldwide plastic production is not comparable with that of concrete, plastic contributes six times more carbon dioxide emissions per volume (1 ton of concrete produces about 1 ton of carbon dioxide).
Huntington Beach, Ca.–based Newlight Technologies utilizes GHG emissions to create a new plastic called AirCarbon. The process involves the conversion of both carbon dioxide and methane, another GHG, into long-chain polymers with the aid of a proprietary catalyst. AirCarbon emulates the composition and functionality of petroleum-based plastics such as acrylonitrile butadiene styrene, polyethylene, and polypropylene. According to NewLight Technologies co-founder and CEO, Mark Herrema, AirCarbon is entirely carbon negative—including the accumulation of the gases as well as the manufacture of the final product. The company now supplies its feedstock to more than 30 companies including KI, Dell, and Ikea. Due to its increasing popularity, “keeping up with demand is our biggest challenge right now,” Herrema told The Guardian in 2014.
Boston-based Novomer also makes polymers from GHG. It similarly creates long carbon chains from undesired emissions, in this case using both carbon and carbon dioxide. Its products focus on rigid foam materials such as foam blocks and panels for use in buildings, as well as footwear and other forms of apparel. Not only can Novomer foams lower the carbon footprint of products like rigid insulation, which contribute around 4 kilograms of carbon dioxide per kilogram (approximately 8.8 pounds per pound) in the case of polystyrene, they can also reduce their flammability.
So how do these concrete and plastic products perform relative to IPCC goals? They provide compelling examples—particularly in the case of carbon-negative plastic—of GHG-reduction objectives that should be addressed in all material sectors. However, like global climate change dialogues, the predominant focus is on reduction of existing emissions, not pulling additional carbon dioxide out of the air. What is required are negative emissions technologies (NETs) which go beyond carbon neutrality towards creating emissions sinks.
Recent research has indicated that concrete is such a sink, absorbing carbon dioxide via its exposed surfaces over its material life. According to findings published in Nature Geoscience, the carbon emissions sequestered in this fashion may offset more than 40 percent of the carbon dioxide produced in concrete generation—although this process can take decades. Scientists at Arizona State University’s Center for Negative Carbon Emissions have proposed using plastic resin to create a carbon-scrubbing machine. Still in the design stage, the large apparatus would deploy plastic sails that absorb carbon dioxide when dry, rewetting them to capture and store the gas.
More research is required to determine the NETs potential in building materials and carbon-cleansing applications. In the coming years, buildings may share the burden of achieving negative carbon emissions—attending to client needs as well as global imperatives. Exactly how they can meet this challenge represents both a significant test and a grand opportunity for architecture.
