In an alternate reality, gradually moving toward a zero-carbon-emission economy and arriving there in two or three decades would be a laudable accomplishment.
In an alternate reality – for example, the reality that might result from turning the clock back to 1975 – a twenty-five year process of eliminating all anthropogenic greenhouse gas emissions could avert a climate crisis.
But in our reality in 2022, with far too much carbon dioxide already flowing through the atmosphere and the climate crisis worsening every year, knowingly emitting more greenhouse gases for another two decades is a shockingly cavalier dance with destruction.
This understanding of the climate crisis guides the work of Bruce King and Chris Magwood. Their own field of construction, they write, can, and indeed must, become a net storer of carbon – and not by 2050 by rather by the early 2030’s.
Their new book Build Beyond Zero (Island Press, June 2022) puts the focus on so-called “embodied emissions”, also known more clearly as “upfront emissions”. The construction industry accounts for up to 15 percent of global warming emissions, and most of the emissions occur during manufacturing of building materials.
No matter how parsimonious new buildings might be with energy during their operating lifetimes, an upfront burst of carbon emissions has global warming impact when we can least afford it: right away.
“A ton of emissions released today,” write King and Magwood, “has far more climate impact than a ton of emissions released a decade from now.”
Emissions released today, they emphasize, push us immediately closer to climate crisis tipping points, and emissions released today will continue to heat the globe throughout the life of a building.
Their goal, then, is to push the construction industry as a whole to grapple with the crucial issue of upfront emissions. The construction industry can, they believe, rapidly transform into a very significant net sequesterer of carbon emissions.
That goal is expressed in their “15 x 50” graph.
By 2050, Bruce King and Chris Magwood say, the construction industry can and should sequester a net 15 gigatonnes of carbon dioxide annually. Graphic from Build Beyond Zero, Island Press, 2022, page 238.
A wide range of building materials are now or can become net storers of carbon – and those that can’t must be rapidly phased out of production or minimized.
The bulk of Build Beyond Zero consists of careful examination of major categories of building materials, plus consideration of different stages including construction, demolition, or disassembly and re-use.
Concrete – by far the largest category of building material by weight and by current emissions –is a major focus of research. King and Magwood outline many methods that are already available to reduce the carbon intensity of concrete production, as well as potential methods that could allow the net storage of carbon within concrete.
Equally important, though, are construction materials that can reduce and in some cases eliminate the use of concrete – for example, adobe and rammed earth walls and floors.
By far the largest share of carbon sequestration in buildings could come from biogenic sources ranging from timber to straw to new materials produced by fungal mycelia or algae.
Harvesting homes
“Tall timber” is a popular buzzphrase for building methods that can sequester carbon within building structures, but King and Magwood are more excited about much smaller plant materials such as wheat straw or rice hulls. Their discussion of the pros and cons of increased use of wood products is enlightening.
“Assessing the degree of carbon storage offered by timber products is not at all straightforward. Far from being the poster child for carbon-storing building, the use of timber in buildings requires a very nuanced understanding of supply chain issues and forest-level carbon stocks in order to be certain we’re not doing harm in the process of trying to do good.” (Build Beyond Zero, page 111)
First, when trees are cut down typically only half of the above-ground biomass makes it into building products; the rest decomposes and otherwise emits its stored carbon back into the atmosphere. Second, particularly where a large stand of trees is clear-cut and the ground is exposed to the elements, much of the below-ground stored carbon also returns to the atmosphere. Third, even once a replacement stand of trees has grown up, a monoculture stand seldom stores as much carbon as the original forest did, and the monoculture is also a big loss for biodiversity.
To the extent that we do harvest trees for construction, then,
“We need to take responsibility for ensuring that we are growing forests at a rate that far exceeds our removals from them. Notice that we are talking about growing forests and not just planting trees.” (page 115)
This careful nuance is not always evident in their discussion of agricultural residues, in my opinion. The “15 X 50” goal includes the conversion of huge quantities of so-called “residues” – wheat straw, rice hulls, and sunflower stalk pith, to give a few examples – into long-lasting building materials. But what effects would this have on the long-term health of agricultural soils, if most of these so-called residues are routinely removed from the agricultural cycle rather than being returned to the soil? What level of such total-plant harvesting is truly sustainable?
Yet there is obvious appeal in the use of more fast-growing small plants as building material. Straw can sequester about twice as much carbon per hectare per year as forests do, while “the carbon sequestration and storage efficiency of hemp biomass is an order of magnitude higher than that of trees or straw.” (page 99)
There are many existing methods to turn small plants into building materials, ranging from structural supports to insulation to long-lasting, non-toxic finishes. It is reasonable to hope for the creation of many more such building materials, if industry can develop new carbon-emissions-free adhesives to help shape fibers and particles into a myriad of shapes. King and Magwood note that existing industrial practices are likely to act as hurdles in this quest:
“Nature provides plenty of examples and clues for making nontoxic bioadhesives in species such as mussels and spiders. However, the introduction and scaling of these potentially game-changing materials is so far hampered in the same way as bioplastics: by an extremely risk-averse construction industry and by a petrochemical industry keen to keep and expand market share ….” (page 162)
Straw-bale construction project in Australia, 2012. Photo by Brett and Sue Coulstock, accessed via Flickr under Creative Commons license.
We don’t have 30 more years
Build Beyond Zero is a comprehensive and clear overview of construction practices and their potential climate impact in the near future. It does not, however, provide any “how-to” lessons for would-be builders or renovators to use in their own projects. For that purpose, both King and Magwood have already published extensively in books such as Essential Hempcrete Construction: The Complete Step-by-Step Guide; Essential Prefab Straw Bale Construction: The Complete Step-by-Step Guide; and Buildings of Earth and Straw: Structural Design for Rammed Earth and Straw Bale Architecture.
In Build Beyond Zero, King and Magwood offer an essential manifesto for anyone involved in commissioning or carrying out construction or renovation, anyone involved in the production of building materials, anyone involved in the establishment or modification of building codes, anyone involved in construction education.
It’s time for everyone involved with construction to become climate-literate, and to realize that upfront carbon emissions from buildings are as important if not more important than operating emissions during the buildings’ lifetimes. It’s time to realize that construction, perhaps more than most industries, has the capability of going beyond zero to become a significant net storer of carbon.
That opportunity represents an urgent task:
“It has taken more than 30 years for energy efficiency to approach a central role in building sector education …. We can’t wait that long to teach people how to make carbon-storing buildings. If we follow the usual path, the climate will be long past repair by the time enough designers and builders have learned how to fix it.” (page 173)
With global greenhouse gases already at catastrophic levels, we have dug ourselves into a deep hole and it’s nowhere near enough to gradually slow down and then stop digging deeper – we also need to fill that hole, ASAP.
As Build Beyond Zero puts it,
“‘Getting to zero,” to repeat one more time, is a lousy goal, or anyway incomplete. You make a mess, you clean it up, as my mother would say. You don’t just stop messing, you also start cleaning.”
Photo at top of page: Limestone quarry and cement kiln, Bowmanville Ontario, winter 2016.
