Zero-Waste Mine Reclamation: Coal + Steel + Human Wastes = Soil

by Zoe Dilles

Coal has seen a worldwide growth in production in recent decades despite health as well as environmental concerns as coal combustion is cited as the primary CO2 atmospheric source. In this age anthropogenic climate change, air emissions often overshadow the threats posed coalmine waste rock, which has far-reaching ecological effects from its metal and acid contents. Mixes of coal waste rock with other substances to balance the concentration of nutrients and minerals can order to promote plant growth. Fabricated soils have the potential to reduce landfill disposal as well as mitigate the issues attendant to reclamation reliant on borrowed soils, often leading to deforestation and hydrologic changes. Continue reading

Determinants of Technology Innovation in the Transportation Sector: Oil Endowments

by Russell Salazar

The development of energy-efficient technologies is becoming increasingly necessary in a warming world. How can countries encourage firms and individuals to innovate more eco-friendly technologies in an effective manner? Kim (2014) takes a closer look at the socio-economic motivators for the development of energy-efficient technologies, with a primary focus on the transportation sector. The study presents empirical evidence to support the claim that smaller oil endowments result in a greater incentive for the development of more eco-friendly vehicles and energy-efficient designs. These findings, combined with explanations from related economic theory, provide insight into potential sustainability schemes for policy makers around the world. Continue reading

Pollution and Politics

by Jackson Cooney

Republican senator, Mitch McConnell, of Kentucky has been pushing states to ignore President Obama’s global warming regulations. He argues that the administration’s anti-coal initiative aims to destroy America’s power generation under the pretense of protecting the climate. The EPA along with the President is requiring each state to submit a plan outlining how they are going to cut coal plant pollution. These plans will lead to the shutdown of hundreds of power plants in the Administration’s attempt to rely more heavily on renewable energy sources. As of now, 12 states have filed lawsuits in protest of this plan. However Senator McConnell has advised that the best way to fight this initiative would be to refuse to submit state plans. Continue reading

Depletion of Fossil Fuels and Climate Change

by Makari Krause

Fossil fuels, while a large part of our energy production, are not a renewable resource and will eventually be depleted. Current climate models, such as the ones used by the IPCC, use levels of future fossil fuel production that Hook and Tang (2013) think are improbable. While fossil fuel combustion currently causes a large part of anthropogenic greenhouse gas emissions, these emissions are linked to fossil fuel production and will decrease as we begin to run out of these resources. There is a multitude of different scenarios that predict future fossil fuel emission and they range hugely in their predictions. The IPCC uses a set of six scenarios called the Special Report of Emission Scenarios (SRES), which are an input for many of their aggregated climate models and influence their conclusions. Hook and Tang question the accuracy of these SRES and aim to review the assumptions that the scenarios make about fossil fuel availability. Continue reading

Way More Methane than EPA Thinks, Maybe

by Emil Morhardt

The amount of the powerful greenhouse gas, methane (natural gas) released into the atmosphere by farmers and gas and oil companies is substantially underestimated by the USEPA according to a team led by Scott Miller, a Harvard Ph.D. student, published late last year in the Proceedings of the National Academy of Sciences. The previously unaccounted sources are ruminants, manure, and fossil fuel extraction and processing in the South-Central US, traced back to their sources from fixed towers and aircraft-based methane sensors using the Stochastic Time-Inverted Lagrangian Transport model (STILT). On the other hand, Hristov et al.(2014), in response to the Miller et al. paper, calculated cattle methane releases from the ground up  based on the number of cattle in the US and thought that the EPA had it right in the first place. So we have a calculation based on numbers of cattle competing with empirical data from the methane sensors processed through an interesting atmospheric model. This type of atmospheric modeling–tracing airborne chemicals back to their source–is what NASA is about to use with the data from its newly launched (July 2, 2014) Orbiting Carbon Observatory, OCO-2, except that the observatory will detect CO2 rather than methane. No public data from it are available as yet, but since methane oxidizes to CO2 in the atmosphere, it is possible that the satellite will soon confirm the sources of the methane. You can find out about the OCO-2 instrument here.

Miller, S.M., Wofsy, S.C., Michalak, A.M., Kort, E.A., Andrews, A.E., Biraud, S.C., Dlugokencky, E.J., Eluszkiewicz, J., Fischer, M.L., Janssens-Maenhout, G., 2013. Anthropogenic emissions of methane in the United States. Proceedings of the National Academy of Sciences 110, 20018-20022.

Hristov, A.N., Johnson, K.A., Kebreab, E., 2014. Livestock methane emissions in the United States. Proceedings of the National Academy of Sciences 111, E1320-E1320.

Please let me know if you are aware of new papers that should be written about by the Climate Vulture


Allowable Carbon Emissions Lowered by Multiple Climate Targets

by Makari Krause

Anthropogenic carbon emissions have been a large factor in climate change since the start of the industrial revolution. Scientists have become increasingly concerned with warming and other effects associated with the release of carbon into the atmosphere. Currently, most world governments have set a target that limits warming to two degrees Celsius since preindustrial times. With this target in place policies are then enacted to limit carbon emissions and hopefully to mitigate anthropogenic effects on earth’s climate. Steinacher et al. (2013) set out to show that setting a target temperature is not sufficient to control many other effects of climate change such as sea level rise and ocean acidification that also result from anthropogenic carbon emissions. They find that when targets are set for these other factors, the allowable carbon emissions are much lower than current targets based on temperature alone.

Steinacher, M., Joos, F., & Stocker, T. F., 2013. Allowable carbon emissions lowered by multiple climate targets. Nature 499(7457), 197–201.


Continue reading

Stray Gases from Shale Gas Extraction Contaminate Drinking Water in Pennsylvania

Shale gas is an unconventional source of natural gas recently made accessible by horizontal drilling and hydraulic fracturing. Shale and other unconventional sources of natural gas have caused overall U.S. production of methane to increase 30% since 2005. Despite their increasing importance, the environmental implications of producing unconventional natural gas have not yet been studied extensively. Jackson et al. explored the possibility of stray gas contamination by testing for concentrations of methane, ethane, and propane in drinking water wells near homes in the Marcellus shale region of Pennsylvania. In general, they found higher amounts of dissolved gases in sources less than one kilometer from a natural gas well. Statistical analysis showed that distance from gas wells was a more significant factor for raised levels of natural gas than other potential sources of contamination. Closer analysis into the chemistry of the samples showed that at least some of the natural gases present in drinking water wells came from a thermogenic source, which includes gas wells. The authors suggest that the stray gases could be due to wells with faulty steel casings or cement sealing.—Shannon Julius
                  Jackson, R.B., Vengosh, A., Darrah, T.H., Warner, N.R., Down, A., Poreda, R.J., Osborn, S.G., Zhao, K., Karr, J.D., 2013. Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction. Proceedings of the National Academy of Sciences 110, 11250-11255

                  Jackson et al. sampled 81 drinking water wells and combined their results with information from 60 previously-collected samples. They measured the concentrations of dissolved methane, ethane, and propane in the water samples and the distance to the nearest gas well from each sample. Other possible sources of natural gas contamination—valley bottom streams and the Appalachian Structural Front—were ruled out using multiple regression analysis, linear regression, and Pearson and Spearman coefficients. In addition, the authors tested to see if the gas came from biogenic sources, i.e. produced by microorganisms, or from thermogenic sources, i.e. with a potential connection to shale gas production. Indicators of thermogenic gas include the presence of ethane or propane, certain isotopic signatures in methane (δ13C-CH4), and the ratio of helium isotope (4He) to methane.
                  The study found dissolved methane at 115 of 141 homes (82%), ethane at 40 of 133 homes (30%), and propane at 10 of 133 homes (8%). Methane had a far higher average than other natural gases in all cases, but homes within one kilometer of a natural gas well had 6 times the amount of methane as homes farther away. The 12 highest concentrations of methane were above the U.S. Department of Interior level for hazard mitigation, and 11 of  those houses were within one kilometer of a gas well. In addition, homes within one kilometer of a gas well had 23 times the amount of ethane as homes farther away, and propane was only detected at homes within one kilometer of a gas well. Ethane and propane only derive from thermogentic sources, so their presence is evidence that the natural gas contamination is likely from a gas well.
                  Another way to determine if gas is from a thermogenic source is to look at the isotopic signature. Yet again the strongest evidence for thermogenic sources (the most δ13C-CH4 signatures greater than –40‰) were within one kilometer from natural gas wells. There is also a trend of shale gas in which isotopes (δ13C) of methane become heavier than those of ethane, though in other cases it is the reverse. Six out of 11 houses where sampling was possible showed this shale gas trend, indicating that those gas samples came from shale gas production.
                  The helium isotope 4He is a component of thermogenic natural gas. The ratio of this isotope to methane (4He to CH4) in the dataset was fairly consistent, except for the points with elevated levels of methane. These had a ratio of 4He to CH4 that was consistant with Marcellus production gases, somewhat lower than normal drinking water levels.
                  The authors contend that poor well construction led to this contamination of drinking water. In particular, stray gases could have escaped through faulty protective steel casings or from imperfections in the cement sealer between the casings and rock outside the well. Faulty steel casings would lead to gas from inside the well leaking out to the surroundings, followed by metals, fracking fluids, or other evidence of gas extraction. Faulty cement would lead to any gas in the spaces around the well to escape upwards into drinking water, meaning the gases would not be easily identifiable with the well itself.

                  The authors would like to see further research to understand more about how drinking water near the Marcellus shale gas production area compares to drinking water near other shale gas sources. They also suggest gathering predrilling data, even making detailed studies of water quality before, during, and after drilling and hydraulic fracturing.             

Demand Management of Oil Will be a Persistent Problem after Peak Production

An eventual peak in oil production is viewed by many to be the unavoidable consequence of the consumption of a resource that is by its very nature nonrenewable. Debate continues as to when this peak will eventually be reached, and it depends largely on our ability to sustain oil production through new methods of exploiting unconventional sources of fossil fuel. Hughes and Rudolph (2010) point out that avoiding a peak depends largely on oil fields that have yet to be discovered, and that unconventional oil sources are costly not only in terms of their energy return on energy invested (EROEI<!–[if supportFields]> XE “Energy Return On Energy Invested (EROEI)” <![endif]–><!–[if supportFields]><![endif]–>), but also with regards to the amount of carbon dioxide expelled in their extraction. When an eventual peak is reached, jurisdictions will primarily be limited to three different methods of coping: reduction of demand for energy, replacement of oil with other sources of secure liquid fuel, and restriction of new demand for energy to sources not based on fossil fuel. The authors conclude that the third option seems more likely, but that problems such as finding clean sources of electricity generation and the difficulty of obtaining natural gas in gas-poor regions would still present significant hurdles to our transition away from oil. —Steven Erickson
Hughes, L., Rudolph, J., 2010. Future world oil production: Growth, plateau, or peak? Current Opinions in Environmental Sustainability special issue Energy Systems.

Hughes and Rudolph (2010) analyzed production and demand growth, sources, alternatives, and production outlooks for oil to reach an opinion on the likelihood of an oil peak. They then proceed to offer possible policy reactions to this peak if it were to occur on a timeline similar to that presented by the International Energy Agency (IEA). They conclude that if a peak due to resource exhaustion were to occur, it would be extremely taxing upon the world’s economies, and the resulting problems would not be overcome in a simple and timely manner.
          Hughes and Rudolph begin by emphasizing the importance of oil in today’s world. They state that oil represents 34% of the world’s total energy demand, with coal<!–[if supportFields]> XE “coal” <![endif]–><!–[if supportFields]><![endif]–> and natural gas making up another 47.4% of aggregate energy demand. This was made possible by the exponential and unprecedented growth of oil production. From the dawn of the 20thcentury all the way through the 1970’s, oil production doubled about once every ten years. Following the oil shocks of 1975 and 1980 growth in oil production has continued, though in a less dramatic linear fashion.
          The authors go on to analyze the sources of this oil production. They say that about 85% of oil is produced from conventional sources, for example onshore reserves and those situated in shallow water. However, these sources have largely been in decline, forcing oil companies to resort to more energy intensive unconventional sources, such as the oil sands of Canada<!–[if supportFields]> XE “Canada” <![endif]–><!–[if supportFields]><![endif]–> or the heavy oil of Venezuela, as well as substitutable liquid fuels such as liquefied coal<!–[if supportFields]> XE “coal” <![endif]–><!–[if supportFields]><![endif]–> and natural gas and fuels created from biomass.
          The main difference pointed out between these two sources is not their ultimate product, but rather the amount of energy required to obtain the fuel. In the beginning of the 20th century it has been estimated that oil reserves in the US had an EROEI<!–[if supportFields]> XE “Energy Return On Energy Invested (EROEI)” <![endif]–><!–[if supportFields]><![endif]–> of nearly 100, while the estimated EROEI of newer conventional crude oil wells is closer to 11, with biofuels currently yielding an EROEI somewhere between 1.0 and 3.2. The authors conclude that if increasing demand for oil is to be met, it will be both expensive and environmentally harmful.
          Hughes and Rudolph move on to address the theory of peak oil. Although peak oil has been criticized for its missed predictions in the past, the authors remind the reader that methods of predicting oil production have been improving and such predictions should not be taken lightly. They examine the production outlooks provided by the IEA, which show an increase in liquid fuel production through 2030. However, the authors point out that this depends largely on crude oil that has yet to be found as well as a growing reliance on liquid natural gas. If either of these prospects do not pan out, a peak or plateau in oil production would likely be reached between 2020 and 2030.
          The authors do state that although the IEA’s study is rigorous, there is a shortage of data regarding oil reserves in the Middle East, as much of these data are unavailable to the public. It is unclear whether this would make IEA under or overestimate the total amount of remaining reserves.
          If a peak occurs, meeting future demand for oil would be an unprecedented challenge to world governments and economies. The authors explain that accommodating such a large change would require long-term planning that would likely require a decrease in energy consumption. Strategies to meet the peak would fall under three main labels: reduction, replacement, and restriction. Reduction would involve lowering energy use through conservation and efficiency, replacement would require replacing oil with other liquid fuels, and restriction would limit new energy demand to non-oil sources.
          Hughes and Rudolph conclude that restriction will be the most likely strategy, and that for at least the near term energy usage would likely be restricted to natural gas and electricity. This of course presents its own unique problems. Providing natural gas to gas poor regions like Europe<!–[if supportFields]> XE “Europe” <![endif]–><!–[if supportFields]><![endif]–> would require either new pipelines or the large-scale liquefying of gas. Either of these solutions would subject places like Europe to intense political pressure from suppliers of natural gas. The major problem with electricity on the other hand is the steady supply of environmentally sustainable energy. Countries like the United States and China<!–[if supportFields]> XE “China” <![endif]–><!–[if supportFields]><![endif]–> have already shown a willingness to rely on their massive coal<!–[if supportFields]>XE “coal” <![endif]–><!–[if supportFields]><![endif]–> reserves, which is not environmentally desirable. The authors state that perhaps the best options are renewables such as solar and wind, despite the fact that they would require a change in energy consumption attitudes, from one where usage determines output to output determining usage.

A Model to Include Risks of Peak Oil in Current Urban Planning

High gasoline<!–[if supportFields]> XE “gasoline”<![endif]–><!–[if supportFields]><![endif]–> prices in 2005 made it clear that spikes in fuel costs will cause people to modify their behaviors. These changes ranged from the increase in consumption of more efficient vehicles, changes in driving behavior such as driving at lower speeds and carpooling, to the reduction of optional trips that an individual may have wanted to take but could not afford. Given these effects, it would make sense for risk models in urban<!–[if supportFields]> XE “urban”<![endif]–><!–[if supportFields]><![endif]–> planning to include risks to certain development forms caused by reduced supply of fossil fuels, but thus far no one has attempted to model these effects. Krumdieck et al. (2010) attempt to rectify this by aggregating various predictions on peaks in conventional oil, they created probabilistic models showing the probability of a peak at a given time and the amount of oil available in the future. They also create impact models to show how these changes will affect behavior and the ultimate value of certain urban developments. Their model showed that the larger the urban sprawl, the greater the calculated risk factor. They conclude that it is essential that transportation risks created by an oil peak must be considered when planning urban areas and that these risks would be best mitigated by concentrating population centers and creating incentives to ride public transportation or use active modes of transportation like cycling or walking. —Steven Erickson
Krumdieck, S., Page, S., Dantas, A., 2010. Urban form and long-term fuel supply decline: A method to investigate the peak oil risks to essential activities. Transportation Research Part A 44, 306–322.

          Krumdieck et al. must first calculate the probable supply of oil in order to know how large of an impact an oil production peak will have on civic life. They create this distribution by fitting a curve to peak projections by various experts rather than trying to pick a single expert to base their claims on. These predictions tend to cluster around 2010, and all of them fall before 2030.  The resulting distribution is bell-shaped and results in a probability function that projects the probability of a peak in a given year. They then take the cumulative probability of this function to calculate the probability that a peak will have occurred by a certain year.
          Then, in order to calculate future oil supply for a given year, similar probabilistic functions need to be estimated in order to find future growth rates and rates of decline. Before peak, growth rates tend to center around 1.6% and estimates of post-peak declines center around 3% per year. A Gaussian probability function was then created for each of these rates.
          Finally, to create the ultimate probabilistic estimation of oil supply, a Monte Carlo simulation was used to integrate the three probabilistic models, generating a set of possible oil supplies spread across a probability function. Among the figures generated by this production, it is predicted that there is only a 5% chance of having more than 28 billion barrels/year in 2035, which is about the yearly production of conventional oil in 2005. The authors suggest that it is likely that by 2035 we will have about 60% of the oil supply as existed in 2005. As urban<!–[if supportFields]>XE “urban”<![endif]–><!–[if supportFields]><![endif]–> planning projects typically look forward as much as 40 years it is clear that an oil peak needs to be considered when looking at potential risks to viability.
          After creating a function for oil supply, an impact function was also necessary to illustrate the effects of an oil peak on individual behavior and aggregate this to find the ultimate effect on various modes of urban<!–[if supportFields]> XE “urban”<![endif]–><!–[if supportFields]><![endif]–> planning. The authors theorize that the primary consequence of rising fuel prices will be a change in travel demand. This will manifest itself by a change in the quantity and nature of trips. They create a metric to measure the essentialiality of trips. Trips are divided into three groups: optional, necessary, and essential. Optional trips are trips that can be cut without an overall loss of utility, necessary trips are trips which an individual would not cut if they could avoid it, and result in a loss of either social or economic wellbeing. Finally, essential trips cannot be cut without significant loss to personal health and overall quality of life. The authors define all trips as 20% optional, 30% necessary, and 50% essential.
          Given the projections on fuel supply produced by the model, it is likely that there will be a disparity between unconstrained—or business as usual—demand and energy supply. Impact is then characterized by the types of strategies available to deal with this disparity, which would depend on organization of the city and transportation methods available. Low impact strategies are defined as those in which energy consumption is lowered but all economic and social participation is maintained. This would be realized by an increase in the use of fuel efficient vehicles, public transportation and active modes of transportation such as walking or cycling as well as through decreased trip distances and other behavioral changes. Medium impact results imply a cut in optional trips. High impact strategies are those in which necessary trips are cut, and very high impact strategies result in a loss of essential trips. The larger the supply and demand disparity, the more difficult it will be to avoid suffering medium and high impact effects.
          These models of fuel supply and supply demand disparity impact are then used to calculate the risk factor of a peak in conventional oil. This model, which incorporates unconstrained energy demand, energy supply, and the various ways in which people can change their behavior to deal with the disparity between the two, comes up with several conclusions. The first is that behavioral changes generate the least impact. These are facilitated by a dense city requiring little driving with good public transportation. The other conclusion is that a reduction to trips significantly increases the risk factor, a possibility faced by more spread out cities with poor public transportation. Although these conclusions seem trivial, the authors point out that this is the first time they have been modeled in a mathematical fashion that can be included in risk analysis models for the planning of future projects.
          In order to test this model, the authors applied their formula to the city of Christchurch, New Zealand<!–[if supportFields]>XE “New Zealand”<![endif]–><!–[if supportFields]><![endif]–>. Christchurch was predicted to nearly double in population between 2005 and 2041, and the city has four different plans for expansion: an unplanned, business as usual approach, Plan A, in which the city borders expand little and the focus is on population density, Plan B, which would allow growth to push out along developed areas, and Plan C, which would primarily involve growth in the suburbs of Christchurch. The development model used had oil supply about 20% over what the model showed was likely for 2041, and risk was calculated with this assumption. Unsurprisingly, although the risk factor was significant for all plans, Plan A had the lowest risk.

Estimating our Commitment to Global Warming

Transitioning from a fossil fuel-based economy to one based on renewable energy is impeded by widespread existing energy infrastructure: not only primary energy infrastructure such as coal<!–[if supportFields]> XE “coal” <![endif]–><!–[if supportFields]><![endif]–>-fired power plants, but also transportation infrastructure such as motor vehicles or airplanes and residential infrastructure such as natural gas-burning furnaces or stoves. Unless this infrastructure is prematurely decommissioned or widely retrofitted with expensive carbon capture and storage<!–[if supportFields]> XE “carbon capture and storage (CCS)” <![endif]–><!–[if supportFields]><![endif]–> technology, this “infrastructural inertia” represents committed CO2 emissions as we move into the future. Davis et al. (2010) calculated the cumulative future emissions of existing energy infrastructure and found that if we completely discontinued the production of net CO2-emitting infrastructure, existing infrastructure alone would contribute 496 gigatonnes of CO2 to the atmosphere between 2010 and 2060, increasing mean global temperatures by 1.3 °C. Noting the difference between this quantity and estimated future warming, the authors conclude that the sources of most emissions are yet to be built. However, they believe that extraordinary efforts are required to prevent the continued expansion of CO2-emitting infrastructure. —Lucinda Block

Davis, S. J., Caldeira, K., Matthews, D., 2010. Future CO2 emissions and climate change from existing energy infrastructure. Science 329, 1330–1333.

          Steven J. Davis and Ken Caldeira of the Carnegie Institution of Washington along with Damon Matthews of Concordia University in Montreal used datasets of worldwide CO2 emissions from directly emitting infrastructure such as power plants and motor vehicles as well as estimates of emissions produced by industry, households, businesses, and other forms of transport to predict cumulative global CO2 emissions through 2060. Historical data provided them with lifetimes and annual emissions of infrastructure. The authors estimated emissions from non-energy sources such as land use change or agriculture<!–[if supportFields]> XE “agriculture” <![endif]–><!–[if supportFields]><![endif]–> using the International Panel on Climate Change’s (IPCC<!–[if supportFields]> XE “Intergovernmental Panel on Climate Change (IPCC)” <![endif]–><!–[if supportFields]><![endif]–>) Special Report on Emissions Scenarios A2 scenario<!–[if supportFields]> XE “IPCC A2 scenario” <![endif]–><!–[if supportFields]><![endif]–>. They used an intermediate-complexity coupled climate-carbon model, the University of Victoria Earth System Climate Model, in order to calculate changes in atmospheric CO2 and temperature based on emissions.
          Davis et al. calculated a cumulative 496 gigatonnes (1 Gt=1012 kg) of global CO2 emissions between 2010 and 2060, with 282 and 701 Gt CO2 being the lower and upper bound estimates. Accounting for non-energy CO2 emissions, the total atmospheric CO2 in this scenario stabilizes below 430 parts per million (ppm), with an increase of global temperatures of 1.3 °C (1.1–1.4 °C above pre-industrial levels or 0.3–0.7 °C above current temperatures). The authors calculate emissions through 2060 (as opposed to through 2100, as with many other climate predictions) because by 2060 all energy-related sources of CO2 emissions are predicted to be no longer functional. Whereas they calculate a mean cumulative emissions of 496 Gt CO2 from existing energy infrastructure, scenarios considering the continued expansion of fossil fuel-based infrastructure through 2100 predict cumulative global emissions of 2986 to 7402 Gt CO2. In those scenarios, global temperatures increase by 2.4–4.6 °C above pre-industrial levels and atmospheric CO2 stabilizes above 600 ppm. Internationally, a rise in temperature of 2 °C and an atmospheric CO2 level of 450 ppm are considered to be the benchmark past which geophysical, biological and socioeconomic systems are especially vulnerable. Thus, the authors note, as existing energy infrastructure does not surpass the benchmark, the infrastructure that represents the most threatening CO2 emissions has yet to be built.
          Existing energy infrastructure is concentrated in highly developed countries such as Western Europe<!–[if supportFields]> XE “Europe” <![endif]–><!–[if supportFields]><![endif]–>, the United States, and Japan and populous countries experiencing rapid development, particularly China<!–[if supportFields]> XE “China” <![endif]–><!–[if supportFields]><![endif]–>. China accounts for the greatest energy inertia, where almost one quarter of worldwide electrical generating capacity has been commissioned as coal<!–[if supportFields]> XE “coal” <![endif]–><!–[if supportFields]><![endif]–> plants since 2000. The young age of its existing infrastructure compared to that of the U.S., Japan, or Western Europe also contributes to China’s large emissions commitment, approximately 37% of the global total. However, emissions commitment per capita in China is comparable to Japan and Western Europe and far less than that of the U.S. (136 tons CO2 per person versus 241). Davis et al. emphasize the importance of historic emissions in already developed countries and consumption in those countries as a driving force of Chinese emissions. They also note that committed emissions per unit of GDP is much higher in developing countries than already developed ones, showing that infrastructural inertia of emissions is greatest where industrialization is occurring but incomplete.
           Davis et al. conclude that although their estimates of cumulative committed global emissions of CO2 do not push us past the threshold of 450 ppm CO2 and 2 °C of warming, avoiding great quantities of CO2 emissions from not yet built infrastructure will require a tremendous political effort and shift, partially because of the supporting infrastructure for CO2 emitting devices such as highways or factories that produce internal combustion engines. Though their findings do not have groundbreaking implications for climate change studies, the study provides a useful benchmark of what future emissions are inevitable without high-cost retrofitting or halting of industry and what future emissions can more easily be reduced.