World map of relative liquid fuel production potential from microalgae, with production potential increasing from blue to orange. Many arid environments in the world’s subtropical coastal regions provide an ideal setting for large-scale cultivation of marine microalgae. Greene et al. Click to enlarge.

Climate, energy, and food security are three of the most important global challenges society faces during the twenty-first century. However, as solutions for mitigating and remediating the effects of climate change are contemplated, they often run into conflict with society’s proposed solutions for ensuring its future energy and food requirements. For example, BECCS [BioEnergy with Carbon Capture and Storage] has been proposed as the primary method for achieving negative CO₂ emissions while simultaneously producing renewable energy on a global scale. However, almost all studies conducted on BECCS so far have focused on terrestrial sources of bioenergy and have concluded that this approach can have many negative consequences for land, nutrient, and water use as well as biodiversity and food production.

In contrast, large-scale ICMM can positively impact climate, energy, and food security while avoiding many of the negative consequences of terrestrial plant-based BECCS. Microalgae exhibit rates of primary production that are typically more than an order of magnitude higher than the most productive terrestrial energy crops. Thus, they have the potential to produce an equivalent amount of bioenergy and/or food in less than one-tenth of the land area. Scaling up production numbers from demonstration-scale cultivation facilities, the current total demand for liquid fuels in the United States can potentially be met by growing microalgae in an area of 392,000 km², corresponding to about 4% of US land area or just over half the size of Texas. The total global demand for liquid fuels can potentially be met by growing microalgae in an area of 1.92 million km², corresponding to about 21% of US land area or slightly less than three times the size of Texas.

—Greene et al.

Further, the authors argue, ICCM avoids environmental challenges such as competition with terrestrial agriculture; excess fertilizer runoff and subsequent eutrophication of aquatic and marine ecosystems; and competition for fresh water.

The Consortium researchers point out that cultivating marine microalgae for biofuel and food not only results in less deforestation, hence less carbon emissions, but agricultural lands reserved for large-scale land crops can be reforested, providing new carbon storage. Marine microalgae grow in seawater, so cultivation facilities could even be located in coastal deserts.

If these algae were grown to the scale of current global fuel needs, they themselves would capture about 28 gigatons of carbon per year. As a comparison, annual anthropogenic carbon dioxide emissions currently measure 40 gigatons globally. If all the algae were burned as fuel or metabolized by animals (including people), then that captured carbon would return to the atmosphere. However, the consequential land-use changes, including reforestation and forests saved by using the algae instead of land plants, can compensate, the authors said. Furthermore, there is the possibility to manufacture algae-based biopetroleum products, like plastics, for longer-term sequestration.

Growing enough algae to provide the current global demand for liquid fuel would also result in residual or remaining algae biomass that could deliver 2.40 gigatons of protein, which corresponds to about ten times the global annual production of soy protein.

The algal proteins, which are high quality, could serve human nutrition, replace soy in animal feed, and substitute for aquaculture fishmeal. Even environmental problems associated with crop fertilizers can take a solution-oriented turn with marine microalgae. Algae do need substantial amounts of nutrients to grow, but they take up nutrients with minimal loss. Further, the MAGIC team offers that the algae could use nutrient-concentrated wastewater instead of fertilizer.

Research and development investments during the next decade will be necessary to further improve the performance and reduce the costs and resource requirements associated with large-scale production of fuels, animal feeds, and human nutritional products from marine microalgae. Ramping up this production to a globally relevant scale will take additional decades to accomplish. By the second half of the century, large-scale ICMM can help society achieve net-negative fossil-carbon emissions; produce the liquid, energy-dense hydrocarbon fuels needed to power the heavy-vehicle, shipping, and aviation components of the transportation sector; and supply the necessary protein to feed an increasingly crowded world.

—Greene et al.

Resources

• Greene, C.H., M.E. Huntley, I. Archibald, L.N. Gerber, D.L. Sills, J. Granados, J.W. Tester, C.M. Beal, M.J. Walsh, R.R. Bidigare, S.L. Brown, W.P. Cochlan, Z.I. Johnson, X.G. Lei, S.C. Machesky, D.G. Redalje, R.E. Richardson, V. Kiron, and V. Corless (2016) “Marine microalgae: Climate, energy, and food security from the sea.” Oceanography 29(4) doi: 10.5670/oceanog.2016.91.