On a hot summer night in 1992, or so we are told by a writer for MIT’s Technology Review, two particle physicists at Los Alamos National Laboratory were staring out over the moonlit desert and sipping cold beers. Given the story that followed, I kind of wonder whether something more aromatic than beer was involved.
“What if,” Klaus Lackner wondered out loud to his companion, Christopher Wendt, “machines could build machines? How big and fast could you manufacture things?” It was not a new idea. Science fiction writers had been drawing from that meme for half a century to populate whole galaxies. But Lackner and Wendt were real scientists, working at a real National Laboratory, the same one that invented the atom bomb.
They decided that the only way the scheme could work would be if you designed robots that dug up all their own raw materials from dirt, harnessed renewables to power the process, and taught succeeding generations of robots to copy themselves. Quoting from Technology Review, March 2019:
They eventually published a paper working out the math and exploring several applications, including self-replicating robots that could capture massive amounts of carbon dioxide and convert it into carbonate rock. “My argument has always been we need to be passive,” Lackner says. “We want to be a tree standing in the wind and have the CO2 carried to us.” The robot armada, solar arrays, carbon-converting machines, and piles of rock would all grow exponentially, reaching “continental size in less than a decade,” the paper concluded. Converting 20% of the carbon dioxide in the atmosphere would generate a layer of rock 50 centimeters (20 inches) thick covering a million square kilometers (390,000 square miles) — an area the size of Egypt.
In 1999, Lackner released a government study titled “Carbon Dioxide Extraction from Air: Is It an Option?” It was a bit starry-eyed, imagining that direct CO2 removal could be accomplished for $15 per ton. The machines that actually do that today require $1000 per ton but many working in the field hope to get that cost down to $600 or even $50 with further investment, at scale. Still, the idea had Lackner in its grip. He left Los Alamos in search of sponsors. Gary Comer, founder of the Lands’ End apparel catalog, gave him $8 million. Lackner founded Global Research Technologies and built a small prototype… and ran out of money. GRT was sold and its buyers went bust, too. The idea’s time had not yet come.
For a generic DAC system in the long term, experts expect the costs for captured CO2 to go down to $37, 87 and 129 per ton CO2 for optimistic, realistic, and pessimistic assumptions, respectively. They estimate rates (in dollars per ton) of 0.12 for capital costs, 0.17 for energy costs and 0.17 for operational and maintenance costs. Under these assumptions, by 2029, DAC will drop capture costs to $55 per ton CO2, with possible further reduction to $28 by 2050 and $17 by 2100.
I have been for many years calling Direct Air Capture technology “artificial trees.” In a recent colloquy with Peter Eisenberger of Global Thermostat, he bristled, responding that each “tree” (a DAC capture unit the size of a shipping container that costs $500,000) can sequester the equivalent of 20,000 to 100,000 natural trees. I’ll have to check his math on that one.
First, the DAC unit is only part of the price, both in dollars and surface area. To go with DAC you need CS (carbon storage) and since DAC produces CO2 in a hot (>212°F) gaseous form that can be frozen and liquified, you’ll also need refrigerated pipelines, deep wells for geologic storage, pumps, etc. Also DACCS (DAC+CS) requires power to run, typically 200–300 kWh-e/tCO2. The cycling of chemicals requires significant heat, 1200–2100 kWh-t/tCO2. Add to the shipping container’s cost and land footprint, a solar array or wind farm, battery storage, road access, fencing, etc. and you are looking at considerably more capital cost (CAPEX) and operating cost (OPEX) than your average tree, or many hundred trees. What is the CAPEX of DACCS compared to the CAPEX of reforestation, on a per tree basis? What is the OPEX? Actually we already know that, because for millennia humans have profitably inhabited forested landscapes, drawing from them most necessities of life. Which of these necessities do artificial trees provide? Just one, it seems: carbon dioxide removal.
To withdraw the 1500 GtCO2 required to keep us under 2 degrees warming this century, builders, be they Lacknerian robots or mere human stainless steel or aluminum welders, would have to produce 51,368,863 artificial trees, each averaging CO2 withdrawals of one ton per day for the next 80 years, at the cost of $25 trillion in capital cost, excluding power plants and pipelines.
Bruce Melton, an engineer who heads the Climate Change Now Initiative and is drafting a carbon neutrality plan for Austin, Texas, responded to Eisenberger that “In WWII we spent $19 trillion dollars globally (2019 dollars) in 7 years, 1939 through 1945, on industrial expansion and mostly heavy manufacturing or $2.71 trillion 2019 US dollars per year. Total global GDP 1939 through 1945 in 2019 US Dollars was $44.6 trillion in 7 years or an average of $6.37 trillion 2019 US dollars per year. Average annual global WWII spending then, was 43 percent of global GDP. If we were to mimic WWII industrialization infrastructure spending today at 43 percent of global GDP of $87 trillion annually in 2019, this would be $37 trillion per year, or $261 trillion in seven years.”
“It’s all about motivation and risk, not money,” Melton concluded.
Of course there are many other problems with technofixes that do not involve money. The chemicals used in sorbent manufacture and the disposal of sorbents at the end of their useful lives must be handled in a responsible way. Sodium hydroxide is highly corrosive and the chlorine gas that is emitted during its production from brine is extremely poisonous. Concentrated CO2 is also potentially deadly. Deep geological storage of the captured carbon gas involves not negligible risk of leakage and upwelling because nowhere is the Earth completely stable. Deep ocean disposal raises issues of salinity, contamination, fragility and cost. The biological carbon pump operates everywhere, even in the deepest depths of the ocean.
Another consideration — which regular readers of this blog will recognize as a recurring theme — is not how long or for what cost it would take to scale artificial trees up to billions of tons carbon sequestration per year, but the opposite — what is the potential to scale down to village and family scale implementation, and to make that worth doing even during the decline phase of a civilization? With other negative emissions technologies — mineral fertilizers, biochar, tree-planting — there is palpable benefit to be harvested at an individual farm-to-kitchen scale. Who would spend $500,000 to have a DACCS container in their village and feed it the heat and electrical energy it requires, with no tangible benefit, assuming this is not a village of robots who have been programmed just to do that?
We are once more confronted with the ideological conflict between wizards like Elon Musk and Bill Gates and prophets like Wendell Berry and Vandana Shiva. It would be sad to see the United States throw trillions at technological chimeras like DACCS when the same money could and should be regenerating the hardwood, evergreen, and chaparral forests we desperately need to stave off the coming climate chaos.shrouded in a black blizzard from the Dustbowl, the 74th Congress appropriated the money for Franklin Roosevelt’s plan to build a great wall of trees from Texas to the Dakotas. Between 1935 and 1939, the Works Progress Administration (WPA), the Civilian Conservation Corps (CCC), and the Forest Service (USFS) planted 217 million trees on 232,212 acres. The New Deal turned back the desert and saved the American breadbasket. Now, since 2000, owing to agricultural subsidies, fencerow-to-fencerow planting, suburban sprawl, and a waning conservation ethic among Plains farmers and their lenders, most of those trees have been cut, burned, and buried where they stood. In Nebraska alone, 57 percent of the original plantings are gone, even as climate change threatens a repeat of the 1930s, on steroids. Whether Roosevelt’s great green wall will be replaced with real trees or artificial ones remains to be seen.
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