Global Carbon Budget 2022:
with overlooked impacts, timber emissions 210% greater than cement.
This discussion highlights the need for parity in environmental reporting with a holistic scope of accountability. We will compare overlooked impacts of two prominent materials whose narratives are well entrenched and widely unquestioned: wood and concrete. Wood is communicated as the savior-designate of climate change; yet its true impact has been consistently overlooked. Cement, the binder in concrete, is targeted for its high-impact production; yet offsetting attributes are ignored.
The good we think we know. It’s renewable. You can grow trees. It stores carbon. New growth absorbs CO2. It’s bio-based. It’s carbon-neutral, isn’t it?
The bad we may not know. The low impact label for wood is solely due to its unquestioned acceptance as a carbon-neutral material, and its glaring lack of accountability. Incredibly, timber harvest emissions are not reported. A "carbon flux" accounting system devised by the timber industry essentially grants an automatic offset for sequestered carbon by tree plantations managed per baseline legal requirements. Thus, timber escapes emissions reporting required of other sectors.1
Multiple studies have independently found the massive influence of old-growth forests vs. logged. The entire forest environment is involved in carbon storage, and it is maximized in undisturbed, old-growth forests, while disturbed, clear-cut, or managed forests bleed substantial amounts of carbon.2
The larger and older the tree, the exponentially more carbon stored. Forest floor undergrowth, including the roots of trees and the soil itself, combine as gargantuan carbon sinks.
Logging disturbs this natural carbon sink. Construction of infrastructure, the equipment that utilizes it, and the harvesting process thereby release enormous amounts of carbon that took lifetimes to sequester.
None of which is considered within current LCA accounting.
"...we estimate that global wood harvests will add 3.5 to 4.2 billion metric tons of greenhouse gases to the atmosphere annually over the coming decades. That’s roughly 10% of recent annual emissions of carbon dioxide. It’s also more than 3 times the annual emissions from aviation and roughly the equivalent of emissions from deforestation and conversion of pastures for agricultural expansion." Searchinger et al.
That which we considered great about timber is also suspect. Yes, you can replant and regrow stands of wood. But it’s not a forest. Such plantations are essentially agriculture with single species harvested well before substantial carbon sequestration. Rates and amounts are a fraction of natural environments.
Wood does absorb and sequester carbon. However, the idea that wood products sequester carbon and thus offset carbon released in their harvesting and manufacturing is overstated. Most wood products will take decades to absorb and sequester the carbon lost in their making, and then only a fraction of it.
A final wood product sequesters as little as 15 percent of the carbon stored in a standing tree.2
Global Carbon Budget 2022:
U.S cement emissions were 0.11% of global fossil fuels and cement emissions.
The bad we think we know. Cement does not have the highest impact per unit of measure. But it is an ingredient in concrete, the most widely used building material globally. The sheer scope of concrete use makes cement’s impact a significant and legitimate issue.
Widely known are the two sources of CO2 in cement’s production – about half from energy inputs, and half from calcination of limestone in the kiln. The industry has been working on mitigating each half with alternative power sources, lower-emission methods, and alternate materials. As attention-getting as "break-through" processes are, the challenge to adoption is in upscaling supply to meet the needs of production at market scale.
But there are products both market-ready and impact-reducing, such as blended Portland Limestone Cement. (See CarbonKind™ Low Carbon CMU.)
It is parroted that cement accounts for 8% of global emissions, but recently published international studies tell a different story. The Global Carbon Project in Global Carbon Budget 20224 (GCB) reports:
2021 global emissions in GtCO2
|Fossil fuels and cement:
|Cement percentage: 4.5%
Note this is a percentage of just the fossil fuel and cement subset, not all known global emissions. Since many reports do not carefully specify if their total emissions are fossil fuels or total global emissions, we chose to compare to the smaller, more prevalent subset.
The good we may not know. Concrete products have an exceptional track record of resilience. But more than that, concrete products also absorb and sequester atmospheric CO2 as noted in the GCB. This begins immediately after it is produced and continues during its service life, in a demolished state, and as a recycled material. (See Carbon Uptake of Concrete Masonry). Research has shown concrete can absorb at least half of its total impact. Half.
GCB 2022 data also includes a 2021 cement carbon sink value of -0.84 GtCO2:
2021 global emissions in GtCO2 including cement carbon sink
|Fossil fuels and cement:
|Cement percentage: 2.2%
It must also be noted the 2021 contribution by cement in the U.S. was 0.04 GtCO24, or 0.11% of global fossil fuels and cement emissions. Typical discussions do not go to that level of detail, so the successful mitigations by U.S. manufacturers may go unnoticed. Thus, lumped together with other global regions that account for most of the global cement impacts, the U.S. cement and concrete industries are disproportionally criticized.
We’ve discussed substantial data overlooked in published narratives. Let’s look at them side-by-side. Taking the lowest value in the range of global wood harvest impacts reported by Searchinger et al, of 3.5 GtCO2 annually:
|Wood harvesting greater by
|Emissions value 1.67
|Emissions value 3.5
|Incl. carbon sink 0.83
Wood has been accepted as a sustainable superhero and cement has been designated enemy number one. Neither mantel has a basis in the whole of scientific study.
The timber industry has received an enormous boost from market and political acceptance of wood as carbon-neutral. Cited references and many others show timber is far from neutral.
Cement is lamented as the most egregious carbon emitter, yet recent studies do not fully support that charge.
Both have impacts, as does everything we do in all aspects of human activities. Informed choices will examine all attributes of considered materials: total impacts, carbon uptake, and resilience.