The anthroposphere (the place where humans live and where human needs are provided for) needs to be recreated to exist within the means of nature. Two important implications can be drawn from this statement: (1) we must use renewable materials that nature provides, and (2) we must not overwhelm natural cycles such that they cease to provide appropriate ecosystem services. The world economy currently uses 70 Gt of materials [1], only 29% of which are renewable (Fig. 1) [2]. Excluding food and fuel from this 70 Gt results in approximately 15Gt of which only 4% is renewable. Human intervention has disrupted nitrogen, phosphorous, water, carbon and other cycles and affected human and ecosystem health through discharges of toxic compounds. 

For example, extracting nitrogen from wastewater requires almost the same amount of energy as fixing nitrogen for fertilizer synthetically from the atmosphere. One-third of the nitrogen synthesized as protein in humans comes from fertilizer that was synthetically fixed from the atmosphere. On the other hand, only about 100 years of minable phosphorous remains, which is essential for agriculture. Altogether, we use about 0.5 Gigaton of fertilizers per year, which are thought to be largely responsible for hypoxia in many coastal water bodies such as the Gulf of Mexico. With respect to carbon, about 9 Gigatons are discharged into the atmosphere annually, which cannot be removed by natural processes at the current pace. Consequently, carbon levels in the atmosphere are increasing and causing climate change. Problems of this massive scale and scope are termed as ‘Gigaton Problems’ [3]. While every incremental solution that attempts to solve these problems is welcome, the magnitude of these problems should always remain in perspective. If a ‘solution’ will address a kiloton of any of the above problems, we would require about a million of those ‘solutions’ to address any of these issues at a meaningful scale. 

The Gigaton problem was created by the billion people in the developed world. By 2050 the world population may reach 10 billion people. Ensuring a secure and safe world requires that all global citizens have sufficient access to the resources necessary to lead useful and productive lives. In other words, the lifestyles of those in the developing world must start to resemble the lifestyles of those in the developed world. Therefore the magnitude of the Gigaton problem will be multiplied by 10 unless new approaches are found. 

Counter intuitively, some aspects of development may curb population growth, thus tempering the magnitude of the Gigaton problem in the future. For example, nearly 5 million children in the developing world die every year from water borne diseases, which are preventable with better water resource development, sanitation, and stormwater control. Higher childhood mortality is one cause of population growth. Women who experience high infant mortality will give birth to more children in hopes that some may survive to adulthood. 

Any potential solution which tries to address any of these Gigaton problems should adopt a two-pronged approach. First, the solutions need to address both the supply as well as the demand side of these problems. While shifting to gasoline-electric hybrid fuel cars substantially reduces the carbon emission per vehicle mile travelled, it would be imprudent to expect that the Earth can support the production, operation and disposal of 8 or 10 billion of those automobiles. There is no conceivable approach to tackle the Gigaton problem without addressing the demands on the anthroposphere. Second, the solutions should be interdisciplinary in nature, addressing the problems simultaneously from the economic, technological and societal perspective. It is imperative to develop an informed citizenry who would facilitate informed decision making, particularly in the socioeconomic sphere. This could in turn lead to sustainable management of the demand side of the Gigaton problem.

References:
[1] 1 Gigaton, abbreviated as Gt, is equal to 1 billion metric tons (10^9). 
[2] Ashby, M.F., Materials and the Environment: Eco-informed Material Choice. Elsevier, 2012, ISBN 0123859727. 
[3] Xu, M., Crittenden, J.C., Chen, Y., Thomas, V.M., Noonan, D.S., Desroches, R., Brown, M.A., French, S.P., 2010. “Gigaton Problems Need Gigaton Solutions,” Environ. Sci. Technol. 44, 4037–4041.

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