One strategy to remove greenhouse gases from the atmosphere and keep long-term global warming to 1.5 degrees is to grow plants that grow quickly, burn them, and then bind and store the CO₂ that is released. However, this puts the stability of the biosphere in jeopardy if it occurs in areas that are not currently used for agriculture. According to a study published in Nature Communications Earth & Environment by the Potsdam Institute for Climate Impact Research (PIK), the potential of these novel “climate plantations”—formally referred to as Bioenergy with Carbon Capture and Storage (BECCS)—is quantified. Not only the CO₂ balance but also other planetary limits are taken into account.

Little results based on current constraints

Less than 200 million tons of CO₂ could be removed outside of current agricultural areas by 2050, according to the study’s assumptions about plant yield, which include no new varieties over time and moderate climate change. In many climate scenarios, this is much less than is anticipated. This implies that existing agricultural areas would have to be used if we wish to rely on this method of CO₂ removal rather than potential alternatives like air filter systems or accelerated rock weathering. This is only possible if our food system shifts and becomes less dependent on animal products, among other things.

Planetary boundaries

The idea of planetary boundaries, which was created in 2009 under the direction of current PIK director Johan Rockström, is being expanded upon by the research team: The foundation of human life is made up of nine processes, ranging from biodiversity to the condition of forests and oceans to the climate, and each process has its limitations. Six limits have already been surpassed, as evidenced by the first planetary health check recently presented by PIK.

Deforestation, freshwater consumption, nitrogen input through fertilization, and the loss of the integrity of the biosphere—which is based on biodiversity, among other factors—are the four land-related issues that are pertinent to the designation and management of climate plantations. For the first time, the new study offers a methodical, process-based model of how the BECCS potential is constrained if these boundaries are not to be crossed.

Computer simulation

The study was conducted as part of the four-year EU project on responsible negative emissions, NEGEM. Wolfgang Lucht, a co-author of the study and head of PIK’s Earth System Analysis research department, says, “Our computer simulation is one of the most sophisticated applications of the biosphere model developed at PIK to date. The current breach of the 1.5 degree limit highlights a crucial point in the ongoing climate debate: in order to effectively address the climate crisis, we must consider other planetary boundaries in addition to the CO₂ balance of measures. In the end, a variety of interrelated processes determine how resilient the Earth system is.”

Theoretically, if all biophysically suitable land outside of present-day agriculture were converted, the potential for CO₂ removal through climate plantations would be much greater than anticipated in the majority of climate scenarios. With BECCS as the primary technology, these project an average of about 7.5 billion tons of CO₂ removal in 2050 to keep global warming to 2 degrees rather than 1.5. However, the situation is reversed when considering planetary boundaries. 

The global biosphere model LPJmL, which simulates water, carbon, nitrogen, and geographical location, shows how much these factors limit the CO₂ removal potential: limiting nitrogen input through fertilizers by 21 percent relative to the theoretical upper limit, protecting freshwater systems by 59 percent, limiting deforestation by 61 percent and avoiding biosphere damage by as much as 93 percent. If all four load limits are kept and existing forests are explicitly protected, the model study shows a potential of less than 200 million tons of CO₂ removal for 2050.

“The most important of all climate protection strategies remains the rapid reduction of emissions towards zero,” concludes Johanna Braun, PIK researcher and lead author of the study. “In order to increase the CO₂ removal potential of climate plantations, i.e. the available area, the world would have to make do with less space and resources in agriculture. In theory, a more plant-based diet could make considerable pastureland available for other uses.”

The study thus points to an important connection, emphasizes Braun: “Producing and consuming fewer animal products not only helps the climate by reducing emissions from agriculture – it also eases the fight for scarce resources and thus protects the earth system as a whole.”