Tread Lightly on the Air
“Tread lightly on the Earth.” —Anonymous
The origins of the above quote are lost to us, but the words summarize the beliefs and goals of the sustainability movement. This movement seeks to balance the needs of humanity with the continued ecological health of the planet and preservation of its biodiversity. A “footprint” has become a metaphor for the impact of humanity as a whole—and of people as individuals—on the environment. This brings us to the latest buzz phrase defining our species’ impact on the rest of the world, our “carbon footprint.” The concept of measuring our environmental impact by means of a footprint originated with a 1992 publication entitled, “Ecological Footprints and Appropriated Carrying Capacity: What Urban Economics Leaves Out,” by William Rees. This paper was later expanded into a book, published in 1996, entitled, Our Ecological Footprint: Reducing Human Impact on the Earth, by Rees and his colleague Mathis Wackernagel of the University of British Columbia (who developed the ecological footprint concept and associated calculation methodologies for his doctoral dissertation). His method of analysis compared the demand on resources by humans by the Earth’s ability to regenerate the resources. The comparison is based on an assessment of the (biologically productive) land and sea area required to provide these resources and absorb the resultant waste materials and pollution.
From this original, general terminology, environmental science has evolved the more specific term of carbon footprint, which focuses on the world’s primary greenhouse gas (GHG), carbon dioxide. In some cases, a carbon footprint has come to be a shorthand reference to the entire range of greenhouse gases produced by human activities. In response to the potential threat of global warming, there has been the development of direct methods for reducing carbon footprints, offsetting their impacts, or effectively trading the cost of managing their impacts by means of “carbon credits.”
What is a Carbon Footprint?
“If you wish to converse with me, define your terms.” —Voltaire
Despite its widespread use, there does not appear to be a single, widely accepted academic or scientific definition of the term carbon footprint. This remains true, despite years of economic and scientific studies that propose to measure the carbon footprint of industries, activities, and even individual people. Often, academics and scientists utilize the term in a way that differs from the accepted meaning for the media and the public.
The word footprint implies a measurement of area. Indeed, the original ecological footprint concept was measured in terms of hectares per person (sorry, America, but the rest of the world uses metric). But, perhaps it is better to think of a carbon footprint in terms of pressure (force applied per unit of area), since it is not just the extent of the footprint but the depth of imprint it makes. This seems more appropriate since carbon emissions are measured in tons.
In addition to whether or not a carbon footprint should include the equivalent impacts of all other greenhouse gases generated by a person, industry, or activity, there is the question of where to start measuring the emissions. In short, should carbon footprints factor in the indirect emissions from production processes used to make a product of just the emissions from the product itself? For example, should only the direct emissions from driving a car be measured, or should the total also include the emissions from the car assembly plant, the steel mill, the rubber factor, or the ore mining operations as well? If a boundary is to be drawn between measuring direct life cycle emissions instead of preproduct activities, where exactly should this boundary be drawn? Can such a boundary be drawn consistently and accurately for a widely diverse group of unrelated products?
Needless to say, these ambiguities have resulted in a variety of often contradictory definitions for a carbon footprint:
“The demand on biocapacity required to sequester (through photosynthesis) the carbon dioxide emissions from fossil fuel combustion.” (Global Footprint Network, 2007)
“A methodology to estimate the total emission of greenhouse gases in carbon equivalents from a product across its life cycle from the production of raw material used in its manufacture, to disposal of the finished product (excluding in-use emissions).” (Carbon Trust, 2007)
“The carbon footprint is a measure of the exclusive total amount of carbon dioxide emissions that is directly and indirectly caused by an activity, or is accumulated over the life stages of a product.” (ISA-UK Research and Consulting, 2007)
This last definition only includes carbon dioxide emissions, not other GHGs. Currently, this is the most widely accepted definition.
Calculating Your Carbon Footprint
“There are three kinds of lies: lies, damned lies, and statistics” —Mark Twain
Carbon footprints can be calculated either by process analysis (PA), or by environmental input/output (EIO). Both methods are designed to assess a product’s or activity’s full life cycle impacts by providing a life cycle analysis (LCA).
PA provides an evaluation of an individual product’s environmental impact from cradle to grave (from when it is first used, to when it is finally discarded). As such, this is a bottoms-up approach severely constrained by boundary conditions that limit the analysis to only onsite and first-order impacts (occasionally, it allows for secondary impacts). PA simply won’t work without well-defined and delineated boundaries. This makes the approach difficult to apply to activities by larger entities, such as governments, industries, or even households. The difficulties arise from the necessity of extrapolating from the individual product to the aggregate. A subset of individual product may not be representative of the whole. Furthermore, groups of activities and products may achieve levels of synergy that escape simple extrapolation (“the whole is greater than the sum of its parts”). Furthermore, analyses of large group activities and product aggregates often have to rely on different (and differing) data bases.
The preferred approach for calculating the carbon footprint for large groups is the EIO, which, in contrast to the PA, is a top-down approach starting with economic data for entire sectors engross. Though comprehensive and free from most contradictory information, the EIO has difficulty providing a detailed analysis or breakdown of the sector in question. However, this lack of emphasis on detail can also be a positive factor, since EIO requires less time and effort to analysis once the computational models have been established. Perhaps the PA would be best utilized as a tool for individual product planners, while the EIO is best suited for analysts studying an entire sector or system.
Actual calculation of an individual footprint involves the summing up of carbon emissions from activities and products that require fossil fuels to operate. Broadly speaking, these are household energy use (including appliances), travel energy usage, and all other activities. These can include annual consumption of electricity from fossil fuel sources (not nuclear or renewable), natural gas, propane, heating oil, direct use of coal, automobile mileage, mass transit mileage (train, bus, and subway), air travel, and sea travel.
The amount of carbon dioxide emissions can vary considerably from type of activity and how comparatively efficient each activity is. Take automotive travel, for example. Driving 10,000 miles per year in a small car, with a rated fuel efficiency of 40 miles per gallons, would generate almost 3 tons of carbon dioxide annually. The same distance traveled per year in a medium-sized car with a rated fuel efficiency of about 20 miles per year, would generate 5.5 tons of carbon dioxide each year. Large automobiles, four-wheel drive autos, and sport utility vehicles with fuel efficiencies of 15 miles per gallon or less can generate up to 8 tons of carbon dioxide annually for the same distance traveled.
Electricity usage can vary considerably from country to country and from region to region. Americans, on average (a somewhat misleading term given the wide diversity of climates and household electrical demand in our country), utilize almost 900 kWh per month. Canadians utilize 750 kWh, Australians 660 kWh, and the British consume less than 300 kWh per month. The amount of electrical usage is affected by the rate of natural-gas usage for heating instead of electrical heating. Furthermore, the amount of carbon-dioxide emissions can very from extensive (for electricity generated by coal fire plants) to literally nothing (for electricity generated by nuclear power plants). Each of the major sources of electricity (coal, natural gas, oil, hydropower, and nuclear) have unique rates of carbon dioxide production, available energy per unit of fuel, and standard-operating efficiencies. For a meaningful comparison, fossil fuels should not be rated for carbon-dioxide production according to identical amounts of fuel but on the resultant (after operational inefficiencies have been factored in) energy produced as measured by Btus. The following table summarizes these comparisons. It does not include hydropower or nuclear, which produce no GHG, or such renewable sources as solar and wind power (for the same reason).
In terms of equivalent energy production, natural gas is six times cleaner than coal and four times cleaner than oil.
Calculations of a carbon footprint resulting from direct heating of the home can be no less complicated. Use of relatively clean natural gas as a heating fuel results in the generation of only one-sixth of a ton of carbon dioxide for every 10,000 feet burned. Fuel oil, on the other hand, apparently produces relatively large amounts carbon dioxide, about 110 tons of carbon dioxide emissions for every 10,000 gallons. But here is where the calculations get tricky and the estimator has to ensure that he is making an apples-to-apples comparison. One cubic foot of natural gas has 1,031 Btus of energy, whereas one gallon of heating oil has 139,000 Btus of energy. So to generate 1 million Btus of energy for household use will require either 970 cubic feet of natural gas or slightly more than 7 gallons of fuel oil. The natural gas will generate 0.015 ton of carbon dioxide to create 1 million Btus. On the other hand, fuel oil will produce 0.077 ton of carbon dioxide to generate the same amount of heat energy. Natural gas is still cheaper, but the difference is not so pronounced. Additionally, each heating system will operate at different efficiencies depending on age and maintenance, among other factors.
It can be seen from the above examples that an accurate assessment of carbon-dioxide production can be very complicated. So, is the calculation of carbon footprints a hopelessly vague task without clearly defined parameters? No more than any other economic activity. All studies have some ambiguity and guesswork, whether it is measuring the core inflation rate, the nationwide “average” price of gasoline at the pump, or the number of man-hours lost to workers surfing the Internet while on the job. And the numbers will always change depending on how the numbers are crunched or the context of their evaluation (President Harry Truman once wished for a one-handed economist, since every economist he ever talked to qualified his statements and predictions with the phrase “on the other hand …”). Yet, imperfect as they are, these statistics and projections are necessary for planning purposes, either at the level of national policy formation or balancing the household checkbook. Just because you can’t know exactly what next month’s gas bill is going to be doesn’t mean you can’t budget your household spending.
Individual families can directly measure their own carbon footprints. It is a relatively simple matter to sum up the average number of miles driven by the family cars each week, factor in their mile-per-gallon rating, and apply a carbon-dioxide emission rate per gallon of gasoline. Businesses can perform similar calculations based on average delivery truck mileage, electrical usage, and office heating requirements. Both are good examples of the bottoms-up process analysis approach. Economists, bankers, government regulators, and environmental scientists will want to examine large aggregates of economic activities, products, and services to determine the true footprint with its often hidden carbon impacts. For example, a hydrogen-fuel-cell automobile, by definition, produces no carbon-dioxide emissions. However, most industrial hydrogen produced in this country is manufactured by the process of steam methane reforming, which extensively utilizes fossil fuels as chemical feedstocks. The EIO approach used to create a big-picture view would have to factor in the carbon emissions from this process, as well as the carbon emissions from the actual mining and extraction of the fossil fuels needed for the process.
Carbon Footprint Reduction, Regulations, and Credits
“Everyone talks about the weather, but nobody does anything about it” —Mark Twain
Make no mistake about it; America has made great strides in the field of controlling and reducing air pollution. According to a 2006 joint report by the Natural resources Defense Council (in cooperation with Ceres, a national coalition of environmental and investor groups, and Public Service Enterprise Group [PSEG], the nation’s 19th largest electrical power company), regulating emission can have a positive impact on air quality and result in significant reductions in air pollutants. The report, from 1990, when the Clean Air Act was amended, through 2004, also states that the 100 largest electric-power companies cut 44% of their emissions of sulfur dioxide, the gas most associated with acid rain. Nitrogen oxides, associated with ozone and smog, have fallen by 36% in the same period. Sulfur-dioxide emissions were reduced from 16 million tons per year to 10 million tons. Nitrogen-oxide emissions showed a similar reduction, from about 7 million tons to 4 million tons. The obvious conclusion: Government regulations really do work in reducing levels of air pollution.
However, carbon-dioxide emissions during the same period rose from 2 billion tons to almost 2.5 billion tons. In 2004, according to the report, the top 100 US power producers were responsible for 39% of carbon-dioxide emissions in the US. As a result of this study and other internal analyses, many within the power-generating industry have already concluded that similar regulations will soon be applied to carbon-dioxide emissions. “We support implementation of a regulatory program that would provide some certainty for the industry, and make a contribution to addressing the global-warming problem, which we think is real and needs to be confronted,” says Neil Brown of PSEG, one of the reports co-authors. Even a harsh global warming skeptic like Exxon has decided that it would rather start bargaining than wait for heavier regulations and has contributed more than $1.25 million to a European Union study on how to store carbon dioxide in natural gas fields in the Norwegian North Sea, Algeria, and Germany.
Carbon credits involve a regulated market for the buying and selling of carbon dioxide emissions. Formally established by the Kyoto Protocol (and similar to the successfully implemented Acid Rain Program in the US), signatories to the accord and subsequent agreements participate in a market for the buying and selling of the ability to emit carbon dioxide. They allow for stringent capping of carbon emissions, while allowing for much needed flexibility in how these caps are met.
Each carbon credit is equivalent to 1 metric ton of carbon dioxide or equivalent amount of another GHG (here is an example of how the definition of “carbon footprint” has been effectively modified to include non-carbon-dioxide emissions). Each operator (source of carbon-dioxide emissions) has an allowance of emission credits. Those that exceed their carbon-dioxide emission reduction goals will end up with excess credits at the end of each year. Their unused quota of credits can then be sold in the carbon-credit market to other operators. Sales can be by a barter exchange of credits, by private sales agreement, or by bidding in open markets similar to any other commodity market. By having a choice between investing in equipment or procedures that reduce carbon-dioxide emissions, or purchasing available carbon credits, operators can chose the most cost-effective means of carbon-dioxide reduction. This greatly reduces the potential rigidity and red tape inherent in regulating carbon-dioxide emissions. As demand for energy increases, this flexibility becomes important for long-term planning.
A possibly unintended side effect of this market has been the creation of companies devoted to the international marketing, buying, selling, and mitigation of carbon credits. The carbon-credit market has its own equivalent of futures markets and brokerage firms. Carbon offsetters are firms that purchase carbon credits from investment funds, or accumulated credits from individual projects. A validation process has been established to ensure the quality and validity of these credits. A related development includes companies that have formed to actively remove carbon dioxide from the atmosphere as subcontractors to operators involved in the carbon credit market. Removal of carbon dioxide from the atmosphere generates credits for their clients, credits that can then be sold on the open market.
Offsetting the Impacts of the Carbon Footprint
“Don’t close the barn door after the horse runs away” —Old saying
Large-scale energy producers already have plans to reduce carbon-dioxide emissions in preparation for what they see as the inevitability of new government regulations. New technologies for carbon sequestration and emission reduction are being developed. For example, Alstom is developing, in conjunction with funder Statoil of Norway, a chilled-ammonia carbon-capture process for isolating carbon-dioxide emissions. The pilot facility (scheduled to begin operations in 2011) will be designed to capture at least 80,000 tons per year of carbon dioxide from flue gases from the refinery’s cracker unit. Use of chilled ammonia allows for energy efficient capture of carbon-dioxide emissions as it reduces the flue gas temperature to 0°C to 10°C. This process results in reduced flue gas volume and increased carbon-dioxide concentrations.
Carbon sequestration is a lower-tech, but effective, approach. Flue gas is captured and literally pumped via a system of pipelines, and pumped into porous rock formations and old oil fields, or reused for industrial processes. The cost effectiveness of this approach makes it comparatively attractive. On average, a 1,000-MW coal-fired power station produces approximately 6 million tons of carbon dioxide annually (that is the equivalent to storing 50 million barrels of carbon dioxide each year). And there is no escaping the fact that refitting carbon-capture equipment to existing plants will represent both a significant capital and operational cost. Including carbon-dioxide removal technology in new coal burning power plant construction is a different story. It is estimated that including this technology in new plants will raise energy costs for households in the US using only coal-fired electricity sources from 10 cents per kWh to 12 cents.
So, what to do about the increased level of carbon dioxide already in the atmosphere? What to do about potentially unregulated carbon dioxide emissions from massively expanded power industries in China and India? Can the amount of carbon dioxide generated since the Industrial Age began, be removed and natural levels restored? Schemes for carbon-dioxide atmospheric removal range from the local to the grandiose. At the local level, the simple planting of more trees can be very effective. Forests already absorb over 10% of carbon dioxide emissions in this country. Trees in urban areas sequester another 2%, and it is here that accumulated individual efforts can have a serious impact. On a grander scale, planting millions of fast-growing trees each year to reforest tropical lands (at the cost of only 10 cents per tree) will remove large amounts of carbon dioxide during their typical 40-year lifetime.
On a truly grand scale are plans to bioengineer the oceans to increase their already high levels of carbon-dioxide absorption. Currently, oceans already sequester one-third of man-made carbon dioxide. A plan to enhance this capability would “fertilize” vast stretches of empty oceans with iron sulfite powder. This acts as a feedstock for massive plankton blooms that absorb carbon dioxide as part of their growth cycle, and then carry the accumulated carbon down to the ocean’s depth when they die. Needless to say, such a grand scheme borders on terraforming the planet. It is fraught with unknowns (will so much carbon dioxide be removed that an ice age is started?) and, given how little we know about their effects, should be approached with the utmost caution. Yet there are startup companies like Planktos Inc. (a for-profit eco-restoration company based in San Francisco with offices in the European Union and British Columbia) that plan to market these services as a means of generating carbon credits for their customers.
However, the one “technology” that could do the most to combat increases in carbon-dioxide emissions is also the one that often gets lost amidst the talk of emission control innovations and new regulations, is simple increases in efficiency. Improved efficiency is the nice “elephant in the room” that hardly anyone talks about. Increased efficiency is rather mundane and far from exciting. Marginal improvements in household appliance efficiency will never grab headlines like a plan to bioengineer the planet. But improved efficiency remains the single best weapon in our arsenal. Over the past few decades, consumer products, packaging, appliances, and utilities have all seen slow, but steady improvement in operational efficiency and reduction in resources required for manufacture. For example, it used to be a real achievement to crush a beer can in your bare hand. Beer cans used to be made with thicker walls and sturdier metal than the thin walled aluminum cans of today.
This is just one example. Driven by market forces demanding decreased costs for shipping, manufacturing, and operation in an evermore competitive global economy, manufacturers continue to reduce their energy and material needs (without being told to by government regulators). Small percentage improvements made each year can have a major effect over time.
It’s the magic of compound interest applied to the environment.
Author's Bio: Daniel P. Duffy, PE, writes frequently on the topics of landfills and the environment.