Calculating the impact of human activity on the environment

(Second of two parts)

The P and A terms are the most common flashpoints of the CO₂ debate between developed and developing countries. India, China, and other developing countries like the Philippines have higher populations than the developed countries, and aspire to have higher standards of living. Some analysts have made cogent arguments for stabilizing population through passive means, for example, better education, access to birth control, and economic development. For a variety of reasons, population policies are fraught with non-scientific issues, and are best left to individual societies to decide. And it is not only the number of people, but also how they are distributed within a nation’s borders that matters. It is clear that high population densities in megacities such as Metro Manila place stress on limited infrastructure. Consider how traffic on EDSA is so much faster over the holidays, when most people are out of the city. This may suggest redirecting people to developing rural areas so that jobs, housing, and social and cultural opportunities are available and may decrease the need for urban migration.

What about the affluence (A) term? From a planetary perspective, the possibility of the Chinese and Indian populations (as examples) consuming as much, driving as much, and wasting as much as the US or EU populations, is catastrophic. And yet it is clearly hypocritical for developed nations to restrict the development of those who seek as high a standard of living as those in the developed countries. Perhaps a better approach is to reexamine the energy- and material-intensive lifestyles in developed countries and find ways to eliminate needless waste. Such wanton excess cannot go on forever in these countries, and should not be the development model or goal of developing countries.  

The final term, the effect of technology T, is the one factor that can save the day. If we accept that controlling population and affluence have profound moral implications, then the only lever we have to reduce impact is technology. The hope is that improvements in technology — particularly in eco-efficiency — will be enough to offset the increases in P and A. Using data from the World Bank (World Development Indicators, http://go.worldbank.org/U0FSM7AQ40), we can calculate the 2000-2005 annual growth rate of CO₂ emissions (the I in this case) as the sum of the growth rates of P, A, and T. The calculations show the challenges ahead. The world net CO₂ growth rate is a positive 3.5 percent. Country-specific analysis shows that the net CO₂ growth rates for China (10.1 percent) and India (3.5 percent) are mostly due to high growth rates in per capita affluence (8.5 percent and 5.2 percent, respectively), and are not offset by the technology gains (expressed as kg CO₂ /$GDP). Interestingly, the Philippines shows a negative 0.9 percent net CO₂ growth rate, largely due to a -5.2 percent growth in T. We have yet to verify and determine the reason for the 2000-2005 increase in eco-efficiency, although initial data (gapminderworld.org) show a stable total CO₂ emissions level while per capita income grew over that period in the Philippines. For comparison, the net CO₂ growth rate in the US is 0.7 percent.        

We can also use the IPAT identity to project CO₂ emissions, into the future. A rough calculation using data from the US Energy Information Administration shows the worldwide CO₂ emissions in the year 2100 would be about 40 GtC (gigatons carbon). This is a little higher than the range given by the International Panel on Climate Change (IPCC), which projected emissions based on many different models. If we use the WRE750 scenario (a well-known emissions pathway to stabilize the atmospheric CO₂ concentration at 750 ppm), we need to lower carbon emissions to 12 GtC in 2100. The implication is that in 90 years, we need to be using energy technologies that will save us the equivalent of 28 GtC, or about four times the total worldwide energy consumed today using today’s technologies.

The challenges to humanity and to each individual are clear. The IPAT identity tells us that we need to work as a society on the P, A, and T terms to ensure that we do not continue to overshoot the ecological capacity of the Earth. International agreements and national policies are needed to mitigate worldwide carbon emissions if we are to avert potentially catastrophic increases in global temperature. But at the end of the day, we all need individual action - we need to appreciate that there is only one Earth, and we need to live within our means.

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Francis L. de los Reyes III is an associate professor of Environmental Engineering at North Carolina State University. He conducts research and teaches classes in environmental biotechnology, biological waste treatment, and molecular microbial ecology. He is on the editorial board of Water Research, and was a 2008 Balik-Scientist of the DOST. He is a member of the Philippine-American Academy of Science and Engineering. E-mail at [email protected].

Joseph F. DeCarolis is an assistant professor of Environmental Engineering at North Carolina State University. He conducts research and teaches classes on energy and climate issues at the intersection of engineering, economics, and public policy. E-mail at [email protected].