It is becoming clear as 2012 approaches that the Kyoto Protocol, which was the international community’s attempt to stabilize the atmospheric greenhouse gas levels through a combination of emission cuts and various economic instruments, will probably not be able to deliver the results initially hoped for. For one thing, the two largest contributors to carbon emissions (China and the US) have opted not to take part in the treaty. Furthermore, many countries that have committed to reductions in carbon dioxide (CO2) emissions, especially those in the EU, have had difficulty achieving the necessary cuts, and may even fail to meet their self-declared targets. A big part of the problem has been the controversy regarding equitable sharing of the burden of making the necessary cuts in CO2 emissions. An argument often made in developing countries is that the carbon stock already in the atmosphere from historical emissions of the developed world are largely to blame, while proposed cuts in emissions only reduce the increment of CO2 added each year to the existing stock. At the same time, small economies may not make much of a difference from the global standpoint — the Philippines, for example, contributes a mere fraction of one percent of the 30 billion tons of CO2 released globally into the atmosphere each year. And yet, paradoxically, it is equally true that the reduction of each ton of CO2 emissions generates the same overall benefit, regardless of where in the world the reduction is achieved. So the debate goes on, and the shape of the post-Kyoto world will be subject as much to political and economic aspects of climate change, as it is to scientific and technological ones.
The root of the problem is that energy (given the current state of technology) is a double-edged sword. On the one hand, energy use is closely linked to economic development and general quality of life; on the other hand, energy use is also intricately linked with greenhouse gas emissions. Thus, as large parts of the world, and Asia in particular, undergo rapid economic growth, energy demand follows accordingly. Global energy demand, which was just under 500 exajoules (EJ) at the turn of the century, is projected to increase to 700 EJ in just a few decades (1 EJ is one billion joules; to put that figure into perspective, one liter of diesel fuel contains roughly 40 million joules of energy). Without any major shifts in energy mix, that growth implies a proportionate increase in annual global greenhouse gas emissions. Thus, the growth of the global energy market results not just in a continuous increase in atmospheric levels of CO2, but the rate at which CO2 is being added is growing as well.
It will be necessary to make significant changes in global energy mix to achieve the necessary reductions in CO2 emissions. In particular, the world needs to make use of an increasing proportion of low-carbon energy sources to meet the growing demand. Many of the technological pieces of the puzzle already exist, but each one of these is subject to its own unique limitations. For example, nuclear energy, which is inherently low-carbon, had been gaining some popularity prior to the Fukushima disaster several months ago. Solar and wind energy are also inherently clean but are highly variable in supply, while hydroelectricity and geothermal power are subject to obvious geographical constraints. Carbon capture and storage (CCS) technology, on the other hand, may be used to render fossil fuel-fired power plants more climate-friendly by removing CO2 from their exhaust gases; however, CCS remains unproven, possibly expensive and definitely controversial. In the transport sector, there has been a global boom in biofuels in recent years, but it is now widely recognized that there is a “photosynthetic ceiling” that limits the potential global supply of bioenergy. The solution may not lie in any one of these technologies individually. In fact, the International Energy Agency advocates the concept of “technology wedges,” where each alternative makes a small but finite contribution to global greenhouse gas emission cuts. In principle, the cumulative effect of combining these technologies will be a dramatic overall reduction in CO2 emissions.
Given that there appears to be no single “magic bullet” that will provide the world with unlimited amounts of clean energy, the obvious question is how to decide which of the available technologies to deploy in specific situations. That is by no means a trivial task, and it is in fact the subject of research inquiry in a branch of chemical engineering widely referred to as process systems engineering (PSE). PSE, which is also known by alternative names (e.g., “computer-aided process engineering” in parts of Europe, and “chemical cybernetics” in Russia), bears little resemblance to the textbook chemical engineering I learned as an undergraduate; PSE dates back to the late 1950s when researchers first recognized the applicability of linear programming to chemical plant design. Today, PSE researchers make use of a broad spectrum of computational techniques to solve process engineering problems, many of which no longer fit within the traditional boundaries of chemical engineering. One such problem is the optimization of energy systems in a carbon-constrained environment, which will be the subject of next week’s column.
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Prof. Raymond R. Tan is a university fellow and full professor of chemical engineering at De La Salle University. He is also the current director of that institution’s Center for Engineering and Sustainable Development Research (CESDR). He is the author of more than 70 process systems engineering (PSE) articles that have been published in chemical, environmental and energy engineering journals. He is member of the editorial boards of the journals Clean Technologies and Environmental Policy, Philippine Science Letters and Sustainable Technologies, Systems & Policies, and is co-editor of the forthcoming book Recent Advances in Sustainable Process Design and Optimization. He is also the recipient of multiple awards from the National Academy of Science and Technology (NAST) and the National Research Council of the Philippines (NRCP). He may be contacted via e-mail at raymond.tan@dlsu.edu.ph.