SciTech

Reversing climate change with carbon sequestration

Credit: Rebecca Enright/Art Editor Credit: Rebecca Enright/Art Editor

Global and U.S. greenhouse gas emissions increased again in 2018. Climate change is far from a won battle. Innovations in energy technology are required to slow the world’s approach to the precipice of climate catastrophe.

On Tuesday, Sept. 17, the Scott Institute for Energy Innovation featured Professor of the Practice and Energy Futures Initiative Principal Joseph Hezir, for a lecture on the novel field of carbon sequestration. Carbon Dioxide Removal (CDR) is the process of removing CO2 from the atmosphere or oceans and storing it in soil, plant matter, and minerals.

In its current state, a large CDR effort is the only way for the world to prevent a 2°C average temperature increase. As carbon emission is reduced, and hopefully eliminated, climate change will still only get worse. Dangerous points of no return have already been passed according to climate scientists from around the globe — a paper from 2007 describes the earth’s permafrost as containing about 25-50 percent of the total quantity of soil organic carbon, atmospheric carbon stored in soil.

Some permafrost has been storing the same carbon for millennia, resilient to the natural heat cycles of the earth. As the permafrost is now heated, this carbon, in the form of CO2 or methane, is released into the atmosphere. Thermokarst, or abrupt thaws, are when ground ice melts and deep, old permafrost pockets are exposed, releasing huge amounts of carbon. These irregular surfaces of land reach deep into the ancient permafrost, belching massive amounts of locked CO2 into the atmosphere. The released carbon then heats the earth through the greenhouse gas effect, which further heats the permafrost, creating a positive feedback cycle that will unlock enough carbon for the permafrost to continue melting catastrophically. It is estimated that 200 billion tons of carbon will be released by the thawing of permafrost over the next few centuries — that’s about 15 percent of the total carbon emitted by industrialization.

Other positive feedback systems include desertification, rainforest decay, peat decomposition, and forest fires. Along with our past emissions, these loops will continue to heat the planet even while industrial emissions are reduced and eliminated. A goal of net zero emissions is insufficient to address the issue of past emissions, which have set in motion what is essentially a boulder rolling down a hill, increasing in speed uncontrollably. There is no chance for an unaided return to pre-industrial climate in the next century. Even if we reduced new emissions to zero, the old emitted carbon will linger in the air for another millennium, heating the planet like an oven.

Our only chance seems to be the removal of carbon from the atmosphere, CDR. Our lingering past emissions pose just as existential a threat to civilization as our current emissions. CDR is one of the few existing technological methods for combating past emissions.

In the lecture, Dr. Hezir introduced a proposal for the creation of a comprehensive three-part, ten-year R&D initiative involving 12 government agencies, with a total funding of $10.7 billion.

Capture technology includes direct air capture, terrestrial and biological storage, carbon mineralization, and coastal and ocean storage. CO2 disposition involves geological sequestration and CO2 utilization. Cross-cutting is the multidisciplinary side of the initiative, focusing on data collection, research into the economics of carbon, and public opinion.

The scale of the global CDR program must be 10 gigatons of CO2 per year by 2050 and 20 gigatons of CO2 per year by 2100 in order to reverse the massive amount of anthropogenic emissions. To put these numbers into context, one gigaton of CO2 was emitted by the entire U.S. light-duty vehicle fleet of 250 million vehicles in 2017. To have a significant impact on climate change, the CDR initiative must develop an industry on the scale of the U.S. steel sector.

For such an industry to be effective, the ten-year research initiative must reduce the cost of every type of carbon capture method and lay the groundwork for massive investment.

In a recently published paper, scientists from the Harvard School of Engineering and Applied Sciences and from the firm Carbon Engineering detailed engineering and cost analysis for a 1 Mt-CO2/year direct air capture plant. This plant would have a levelized cost of $94 to $232 per ton CO2 from the atmosphere. “This design reflects roughly 100 person-years of development by Carbon Engineering,” stated the paper.

This bi-circular process is facilitated by four major components, the contactor, the pellet reactor, the calciner, and the slaker. First, the contactor brings ambient air and an alkaline solution together, effectively “trapping” the ambient carbon in potassium carbonate. Next, the pellet reactor adds calcium ions into the carbon saturated solution, causing the precipitation of CaCO3 or calcite. Water is also removed in this step. Then, these calcite pellets are heated, yielding calcium oxide, and the pure CO2 now removed from the air, can be compressed, sequestered, and used in industry. Finally, heat from the slaker is used to dry and preheat the pellets, yielding sufficient steam to further the reaction.

But other carbon capture methods are equally important. The U.S. government’s Advanced Research Projects Agency has been developing a new technology which enhances the roots of wetland plants to store carbon in a more resilient fashion. Wetlands can be expanded into low vegetation lowlands, and reforestation can store carbon in massive amounts. Ocean algae remove massive amounts of carbon from the air but are threatened by ocean acidification. Carbon can be mineralized into solids and stored underground, but today the cost of these methods are too high to be implemented on a significant scale.

Carbon taxes are a surefire way to reduce emissions to required levels. An implementation that allocates the collected funds into research and production of new energy production systems. However, carbon taxes are politically unviable in today's political climate.

Professor Hezir had a message for young engineers, champing at the bit to create impactful innovations. The techniques outlined will decrease the cost of carbon sequestration, he said, but we need real breakthroughs in creating processes which efficiently convert forms of carbon into materials, energy, and production.