By Victor Miguel Ponce

Many people are concerned about global warming, but they do not know what to do about it. The first thing is to understand the problem and its apparent root cause: the burning of fossil fuels.

The concentration of carbon dioxide in the atmosphere determines to a large extent the present world climate, with temperature being an important component. Through geologic time, carbon dioxide entering the atmosphere from natural sources such as volcanic eruptions and weathering of rocks, has been gradually used by vegetation, through the process of photosynthesis. In the past 2.5 billion years, carbon has been temporarily stored above the Earth's surface as standing biomass and litter. During this time, excess quantities of carbon were permanently stored below the surface as fossil deposits of coal, petroleum, and natural gas.

In the past 600 million years, as animals developed and evolved, they began to return some of the carbon stored in the standing biomass back to the atmosphere, since they live by eating and burning food, i.e., organic matter. This process, called respiration, returns carbon dioxide to the atmosphere and replenishes it. There is a natural balance ("dynamic equilibrium") between outputs and inputs of carbon dioxide: outputs through photosynthesis and inputs through respiration.

Enter the modern human. In the past 250 years, humans have developed machines to support economic development. In the past four decades alone, the population of the world has doubled, and the numbers of machines have grown substantially. These machines are truly artificial animals, since they burn fuel, which is normally organic matter. To power the machines, humans have learned how to burn fossil fuels, i.e., the surplus carbon stored in the soil substrate through geologic time. The indiscriminate burning of fossil fuels is threatening to throw the delicate balance of nature into a spin: More carbon now enters the atmosphere than can be extracted from it by natural means.

Scientists believe that some of this excess carbon is being stored in the biosphere as additional plant biomass. Another fraction is surely being sequestered in the oceans in quantities that may prove to be largely intractable. Still, conclusive studies show that a sizable fraction of the excess carbon dioxide is accumulating in the atmosphere. According to the Scripps Institution of Oceanography, the records at Mauna Loa, Hawaii, show an increase in the mean annual concentration of carbon dioxide, in the middle layers of the troposphere, from 316 ppm in 1959 to 403 ppm in 2016, i.e., a 27% increase in the past 58-yr period.

Indeed, the fossil fuels could be taken as nature's surplus energy, accumulated through geologic time in the soil substrate, effectively sequestered in order for the world's present climate to be preserved. This is the predicament of modern civilization: The fossil fuels were put away by nature; taking them out (in a comparatively short time) at rates exceeding natural absorption is bound to upset the world's present climate.

The obvious solution is for global society to rethink development to gradually move away from fossil fuels. The aim should be toward the much-heralded, but still elusive, sustainable type of development. Sustainable development is based on renewable forms of energy, such as solar, wind, hydro, and biomass. This is technically feasible, yet its implementation is sure to require uncommon leadership. Furthermore, the issue of global warming poses a significant ethical dilemma: the choice between good and bad fuels. Good fuels are those that are renewable, i.e., they cannot be stored beyond one generation. Bad fuels are those that are fossil, stored in the Earth's substrate through millennia, and intended by nature to be put away so that the present world's climate, in which humans evolved, could be preserved.

Victor Miguel Ponce is professor of civil and environmental engineering at San Diego State University. His specialty is hydrology, environmental science, and sustainable development.

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