What does it mean to close the carbon cycle?
Tomorrow starts the 7th rendition of the “Closing the Carbon Cycle: Fuels from Air” in at Arizona State University that I have had the pleasure to organize. For three days, speakers hailing from academia, industry, finance, and law will come together to present and discuss a variety of options that are connected to closing the carbon cycle. (If you are reading this and are in Tempe AZ, and are free Wednesday to Friday, you are welcome to come).
What is the carbon cycle and why does it need closing?
Carbon is a crucial element found in many different locations in our earth and atmosphere. The carbon cycle is nature’s way of cycling this element through different reservoirs with processes like photosynthesis, respiration, weathering, and fossilization.
Because we mobilize the carbon stored in fossils to make energy, the carbon cycle is open. New carbon is released into the atmosphere as carbon dioxide or methane, and while the oceans and biomass grab about half of what we emit, the other stays there adding to the greenhouse effect.
The bad news is that as the world continues to emit, the ocean and land sinks are actually getting less effective at storing carbon. Even worse, the climate math gives us an extremely small window of time to keep atmospheric CO2 levels below what they need to be, and without immediate and deep decarbonization we will quickly spend our carbon budget. Time is quickly running out for making the lowest cost decisions to mitigate climate pain.
Good news? There are plenty of promising options out there that collectively can close the carbon cycle and deal with this externality.
Reduce emissions. We can slow down the flow of carbon to the atmosphere with well-understood solutions that allow us reduce the amount of carbon that we put there in the first place and become more efficient.
Capture carbon at centralized sources. We can capture the carbon at the emissions and continue to burn fossil fuels with carbon capture and storage. However, this does not completely close the carbon cycle because only 90% of the emissions are captured (actually this is more like only capturing 87% because of a 30% parasitic load and the additional emissions in the extraction of fossil fuels).
Carbon free energy. We can create energy with carbon free sources from hydro-electric, solar, wind, hydrogen, and nuclear. As long as this type of electricity can fuel battery-powered vehicles, much of the transport sector can go carbon neutral. However it is critical to consider the embedded carbon that goes into making this energy.
Carbon neutral hydrocarbons. Not all vehicles will go electric, and for shipping and aviation this is even more difficult. However if the source of carbon for the fuel comes from the atmosphere it is carbon neutral (minus the carbon emitted in the embedded energy in the infrastructure). There are many pathways that include electrochemical, thermochemical, using radiative energy, or plasma splitting conversion.
Use biomass to make energy and sequester carbon. We can burn, capture, and store biomass, or BECCS (Bio Energy with Carbon Capture and Storage). We can also expand technologies that can convert waste into energy.
Enhance natural sinks. Soil carbon can become a greater sink with simple land management techniques. We can plant more trees.
Air capture with carbon storage. Ultimately closing the carbon cycle means restoring the carbon balance. If a ton of CO2 is emitted from fossils, then another ton of CO2 must be put away. This requires a backstop that can set the upper cost of carbon remediation.
The maturity and commercial readiness of many of these ideas varies widely. Some of them are woefully under-invested in because they can’t make money today. But if we aren’t able to do, then we can’t learn. And to do means an all out effort that recognizes the need to go down the learning curve in a hurry with urgent investment in the most promising solutions to close the carbon cycle.
