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New quasi-experimental research finds major impact of coal emissions on health.
By: Peter Dizikes

A high level of air pollution, in the form of particulates produced by burning coal, significantly shortens the lives of people exposed to it, according to a unique new study of China co-authored by an MIT economist.

The research is based on long-term data compiled for the first time, and projects that the 500 million Chinese who live north of the Huai River are set to lose an aggregate 2.5 billion years of life expectancy due to the extensive use of coal to power boilers for heating throughout the region. Using a quasi-experimental method, the researchers found very different life-expectancy figures for an otherwise similar population south of the Huai River, where government policies were less supportive of coal-powered heating. 

“We can now say with more confidence that long-run exposure to pollution, especially particulates, has dramatic consequences for life expectancy,” says Michael Greenstone, the 3M Professor of Environmental Economics at MIT, who conducted the research with colleagues in China and Israel.

The paper, published today in the Proceedings of the National Academy of Sciences, also contains a generalized metric that can apply to any country’s environment: Every additional 100 micrograms of particulate matter per cubic meter in the atmosphere lowers life expectancy at birth by three years.

In China, particulate-matter levels were more than 400 micrograms per cubic meter between 1981 and 2001, according to Chinese government agencies; state media have reported even higher levels recently, with cities including Beijing recording levels of more than 700 micrograms per cubic meter in January. (By comparison, total suspended particulates in the United States were about 45 micrograms per cubic meter in the 1990s.)

Air pollution has become an increasingly charged political issue in China, spurring public protests; last month, China’s government announced its intent to adopt a series of measures to limit air pollution.

“Everyone understands it’s unpleasant to be in a polluted place,” Greenstone says. “But to be able to say with some precision what the health costs are, and what the loss of life expectancy is, puts a finer point on the importance of finding policies that balance growth with environmental quality.”

A river runs through it

The research stems from a policy China implemented during its era of central planning, prior to 1980. The Chinese government provided free coal for fuel boilers for all people living north of the Huai River, which has long been used as a rough dividing line between north and south in China.

The free-coal policy means people in the north stay warm in winter — but at the cost of notably worse environmental conditions. Using data covering an unusually long timespan — from 1981 through 2000 — the researchers found that air pollution, as measured by total suspended particulates, was about 55 percent higher north of the river than south of it, for a difference of around 184 micrograms of particulate matter per cubic meter.

Linking the Chinese pollution data to mortality statistics from 1991 to 2000, the researchers found a sharp difference in mortality rates on either side of the border formed by the Huai River. They also found the variation to be attributable to cardiorespiratory illness, and not to other causes of death.

“It’s not that the Chinese government set out to cause this,” Greenstone says. “This was the unintended consequence of a policy that must have appeared quite sensible.” He notes that China has not generally required installation of equipment to abate air pollution from coal use in homes.

Nonetheless, he observes, by seizing on the policy’s arbitrary use of the Huai River as a boundary, the researchers could approximate a scientific experiment.

“We will never, thank goodness, have a randomized controlled trial where we expose some people to more pollution and other people to less pollution over the course of their lifetimes,” Greenstone says. For that reason, conducting a “quasi-experiment” using existing data is the most precise way to assess such issues.

In their paper, the researchers address some other potential caveats. For instance, extensive mobility in a population might make it hard to draw cause-and-effect conclusions about the health effects of regional pollution. But significantly, in China, Greenstone says, “In this period, migration was quite limited. If someone is in one place, the odds are high they [had always] lived there, and they would have been exposed to the pollution there.”

Moreover, Greenstone adds, “There are no other policies that are different north or south of the river, so far as we could tell.” For that matter, other kinds of air pollution, such as sulfur dioxide and nitrous oxides, are spread similarly north and south of the river. Therefore, it appears that exposure to particulates is the specific cause of reduced life expectancy north of the Huai River.

In addition to Greenstone, the paper has three other co-first authors: Yuyu Chen, of the Guanghua School of Management at Peking University; Avraham Ebenstein, of Hebrew University of Jerusalem; and Hongbin Li, of the School of Economics and Management at Tsinghua University. The research project received funding from the Robert Wood Johnson Foundation and the National Natural Science Foundation of China.

Another reason to limit emissions

Scholars say the paper is an important contribution to its field. Arden Pope, an economist at Brigham Young University and a leading researcher in environmental economics and air pollution, calls it “one of the most dramatic and interesting quasi-experimental studies on the health effects of air pollution that has been conducted.” At the same time, Pope observes, the results are “reasonably consistent” with other air-pollution research using different study designs.

Pope notes that while many air-pollution studies have occurred in the United States and Europe, “It is important to conduct studies in China and elsewhere where the pollution levels are relatively high.” Going forward, he suggests, it would also be desirable for researchers to look for ways to specifically study the health effects of fine particles, those less than 2.5 micrometers in diameter. 

Greenstone notes that the researchers were not sure what result they would find when conducting their study. Still, he says of the finding, “I was surprised by the magnitude, both in terms of [the quantity of] particulates, and in terms of human health.”

Greenstone says he hopes the finding will have a policy impact not only in China, but also in other rapidly growing countries that are increasing their consumption of coal. Moreover, he adds, given the need to limit carbon emissions globally in order to slow climate change, he hopes the data will provide additional impetus for countries to think twice about fossil-fuel consumption.

“What this paper helps reveal is that there may be immediate, local reasons for China and other developing countries to rely less on fossil fuels,” Greenstone says. “The planet’s not going to solve the greenhouse-gas problem without the active participation of China. This might give them a reason to act today.”

June 17, 2013
Vicki Ekstrom
MIT Energy Initiative

Energy efficiency promises to cut emissions, reduce dependence on foreign fuel, and mitigate climate change. As such, governments around the world are spending tens of billions of dollars to support energy-efficiency regulations, technologies and policies.

But are these programs realizing their potential? Researchers from the MIT Energy Initiative (MITEI) and University of California at Berkeley’s Haas School of Business have collaborated to find out.

The researchers’ energy-efficiency research project, dubbed “E2e,” is a new interdisciplinary effort that aims to evaluate and improve energy-efficiency policies and technologies. Its goal is to support and conduct rigorous and objective research, communicate the results and give decision-makers the real-world analysis they need to make smart choices.

The E2e Project is a joint initiative of the Energy Institute at Haas and MIT’s Center for Energy and Environmental Policy Research (CEEPR), an affiliate of MITEI — two recognized leaders in energy research.

The project’s name, E2e, captures its mission, the researchers say: to find the best way to go from using a large amount of energy (“E”) to a small amount of energy (“e”), by bringing together a range of experts — from engineers to economists — from MIT and UC Berkeley. This collaboration, the researchers say, uniquely positions the E2e Project to leverage cutting-edge scientific and economic insights on energy efficiency.

“Cutting energy has lots of potential to help us save money and fight climate change,” says Michael Greenstone, MIT’s 3M Professor of Environmental Economics and a member of MITEI’s Energy Council. “It’s critical to find the local, national and global policies with the biggest bang for the buck to use governments’, industry’s and consumers’ money wisely while slowing climate change.” 

Greenstone is leading the project with Christopher Knittel, co-director of CEEPR, and Catherine Wolfram, associate professor and co-director of the Energy Institute at Haas.

“When deciding on the best energy measures to implement, decision-makers should compare model predictions to actual consumer behaviors. That’s where this project comes in,” Wolfram says. “The E2e Project is focused on singling out the best products and approaches by using real experiments centered on real buying habits. It will provide valuable guidance to government and industry leaders, as well as consumers.”

The group’s motivations for studying energy efficiency are derived, in part, from the McKinsey Curve — a cost curve that shows that abating emissions actually pays for itself.

“Our goal is to better understand what the costs and benefits of energy-efficient investments are — where the low-hanging fruit is, as well as how high that fruit is up the tree,” says Knittel, MIT's William Barton Rogers Professor of Energy Economics at the MIT Sloan School of Management. “The McKinsey curve would suggest the fruit’s already on the ground. If this is true, we want to figure out why no one is picking it up.”

Former U.S. Secretary of State George P. Shultz, a member of the E2e advisory board, says, “I like the saying ‘A penny saved is a penny earned,’ which rings true from the standpoint of energy. Energy that is used efficiently not only reduces costs, but is also the cleanest energy around. The E2e Project will allow us to better understand which energy-efficiency programs save the most pennies.”

Shultz is a distinguished fellow at Stanford University’s Hoover Institution, where he leads the Energy Policy Task Force. The board also includes MIT Institute Professor John Deutch, former undersecretary of the Department of Energy; Cass Sunstein, a professor at Harvard Law School and President Obama’s former director of regulatory affairs; Susan Tierney, managing principal at Analysis Group and a former Department of Energy official; and Dan Yates, CEO and founder of Opower.                                                           

The E2e Project seeks to answer questions such as: Are consumers and businesses bypassing profitable opportunities to reduce their energy consumption? What are the most effective ways to encourage individuals and businesses to invest in energy efficiency? Are current energy-efficiency programs providing the most savings?

The project’s first experiments are already underway. For example, the team is tracking consumers’ vehicle purchasing decisions to discover if better information about a car’s fuel economy will influence consumers to buy more fuel-efficient vehicles. If so, emphasizing the calculated fuel savings in the vehicle information presented to consumers may be productive. 

Other initial projects include evaluating the Federal Weatherization Assistance Program, and determining why households invest in energy efficiency and the returns to those investments.

More information: e2e.haas.berkeley.edu or e2e.mit.edu

The E2e Project was funded with a grant from the Alfred P. Sloan Foundation.

June 14, 2013
Alli Gold
MIT Joint Program on the Science and Policy of Global Change 

After the 2011 Fukushima nuclear disaster, energy experts and policymakers around the world began to reassess the future of nuclear power. Countries, including Japan and Germany, have since scaled back or plan to shut down their nuclear power — sparking a global debate on how nations will replace nuclear.

Taiwan is just one country where this intense debate is unfolding. Yen-Heng Henry Chen, a Taiwan native and research scientist at MIT’s Joint Program on the Science and Policy of Global Change, decided to look at how the nation’s economy and emissions reduction strategies might be affected by future changes to Taiwanese nuclear energy policies.

“There has been little research on the interactions between non-nuclear and low-carbon policies,” Chen says. “Taiwan has a small economy and limited natural resources, making it an interesting case study for other countries looking for ways to cut carbon emissions with or without nuclear power.”

The Taiwanese government aims to cut its CO2 emissions in half (from 2000 levels) by 2050. One way they had planned to do this was through nuclear power. Taiwan currently has three nuclear power plants, with plans to bring a fourth plant, the Longmen Nuclear Power Station, online in 2015. This tightly populated country has more than nine million residents within 50 miles of its three existing nuclear reactors. Because Taiwan is similar in topography and fault lines to Japan, the prospect of the new plant — and perhaps others to come — has raised public concerns about the safety of nuclear power.

“After the Fukushima accident, more than 60 percent of the Taiwanese population was against the construction of a new nuclear power plant according to a recent poll,”  Chen says. “I wanted to know what it would mean for the Taiwanese economy and the government’s emissions reduction targets if they were to eliminate or reduce nuclear power.”

Taiwan currently imports 99 percent of its energy, which includes oil, natural gas, coal and nuclear. Because the opportunities for alternative low-carbon energies such as solar, wind and hydro are limited, Chen conducted an economy-wide analysis that explored other ways to reduce carbon emissions: nuclear power, a carbon tax, and carbon capture and storage (CCS) technology.

When implementing a low-carbon and non-nuclear policy, without the availability of CCS (which is not yet cost-effective at a large scale), Chen finds that by 2050 GDP would drop by about 20 percent. If CCS were to become more cost-effective and could be added to the low-carbon strategy, GDP would drop by less than 10 percent. But the least expensive way to pursue a low-carbon policy, Chen finds, would be to expand nuclear capacity in addition to adopting CCS. If nuclear capacity was tripled (compared to current levels) and CCS option was feasible, by 2050 GDP loss would be reduced to around five percent.

Absent nuclear power and CCS, “Taiwan needs to convert its industrial structure into a much less energy intensive one if the country is serious about achieving a low-carbon environment,” Chen says. Taiwan’s industrial sector accounts for almost half of the country’s energy demands.

Costs could be lowered for industry and consumers if Taiwan were able to join an international emissions trading system — which Chen looks forward to exploring further in future research.

Until such an international trading system exists, “This case study can help policymakers better understand the costs of cutting CO2 emissions without nuclear energy,” Chen says, “as nuclear power becomes a less viable energy solution in Taiwan and around the world.”

June 13, 2013
Alli Gold
MIT Joint Program on the Science and Policy of Global Change

If you know how much something costs, you can budget and plan ahead. With this in mind, a team of researchers from MIT, the World Bank and the International Food Policy Research Institute recently developed a country-level method of estimating the impacts of climate change and the costs of adaptation. This new method models sector-wide and economy-wide estimates to help policymakers prepare and plan for the future.

"Previous country-level research assessing climate change impacts and adaptation either focused on economy-wide estimates or sector-by-sector analysis, without looking at the bigger picture," says Kenneth Strzepek, one of the lead authors of the study and a research scientist at MIT's Joint Program on the Science and Policy of Global Change. "By looking at the interplay between different sectors and within the economy, we are able to evaluate the indirect effects and interactions that can occur that are often not captured."

As a case study, the researchers apply their technique to Ethiopia — the second most populated country in Sub-Saharan Africa. They look at three key sectors: agriculture, road infrastructure and hydropower.

"These sectors were selected because of their strategic role in the country's current economic structure and its future development plans," Strzepek says.

Agriculture accounts for about 46 percent of the GDP in Ethiopia and is almost entirely rain-fed. Variability in temperature and rainfall will have major impacts on this crucial industry. The researchers found that with a temperature increase of two degrees Celsius, more intense drought and floods will cause a drop in crop production — triggering reductions in income, employment and investments.

Frequent and intense flooding will also damage Ethiopia's road infrastructure — the backbone of the country's transportation system and a needed link in the agricultural supply chain. The researchers found that flooding brought on by climate change will increase maintenance costs by as much as $14 million per year for the existing road network, which is expected to grow dramatically in the next 40 years.

The intense variability of precipitation will also greatly impact the country's hydropower and associated reservoir storage, which could provide energy, irrigation and flood mitigation. Because there is currently little installed hydro capacity in Ethiopia, the model showed few climate change impacts. But in the coming years, the government plans to invest heavily in this sector, meaning there could potentially be significant impacts to this sector as well.

Additionally, the researchers found that there would be an increased demand for water across sectors and create challenges for policymakers to effectively distribute this important resource. For example, Ethiopia plans to expand irrigated agriculture by 30 percent by 2050. The researchers found that some of the irrigation demands will be unmet, placing demands on other sectors requiring water resources.

"This research makes clear the impact droughts, floods, and other effects brought on by climate change can have on major financial sectors and infrastructure," Strzepek says. "For Ethiopia, we find that one of the best defenses against climate change is investment in infrastructure for transportation, energy and agriculture. By building up these sectors, the government will be able to enhance the country's resiliency."

He continued, "In predicting the outcomes of future water, infrastructure and agriculture projects, we were able to test the effectiveness of policies. This gives decision-makers in these countries, as well as international organizations, the information they need to continue to grow, develop and plan for the future with climate change in mind."

Planning for climate change is essential, Raffaello Cervigni, a co-author of the study and lead environmental economist at the World Bank, writes in a recent blog post.

"Addressing climate change is first and foremost a development priority for Africa … If no action is taken to adapt to climate change, it threatens to dissipate the gains made by many African countries in terms of economic growth and poverty reduction over the past ten years," he writes.

But, he continues, "a harsher climate need not be an impediment for Africa's development," if we can come together to address these challenges.

The integrated approach used by the authors is now being applied to studies on the costs of adapting to climate change in Ghana and Mozambique, as well as Vietnam. Others have replicated the approach to help other countries calculate the costs of adaptation.

Reprint 2013-7

June 6, 2013
Vicki Ekstrom, MIT Energy Initiative

The cost and performance of future energy technologies will largely determine to what degree nations are able to reduce the effects of climate change. In a paper released today in Environmental Science & Technology, MIT researchers demonstrate a new approach to help engineers, policymakers and investors think ahead about the types of technologies needed to meet climate goals.

“To reach climate goals, it is important to determine aspirational performance targets for energy technologies currently in development,” says Jessika Trancik, the lead author of the study and an assistant professor of engineering systems. “These targets can guide efforts and hopefully accelerate technological improvement.”

Trancik says that existing climate change mitigation models aren’t suited to provide this information, noting, “This research fills a gap by focusing on technology performance as a mitigation lever and providing a way to compare the dynamic performance of individual energy technologies to climate goals. This provides meaningful targets for engineers in the lab, as well as policymakers looking to create low-carbon policies and investors who need to know where their money can best be spent.”

The model compares the carbon intensity and costs of technologies to emission reduction goals, and maps the position of the technologies on a cost and carbon trade-off curve to evaluate how that position changes over time.

According to Nathan E. Hultman, director of Environmental and Energy Policy Programs at the University of Maryland’s School of Public Policy, this approach “provides an interesting and useful alternate method of thinking about both the outcomes and the feasibility of a global transition to a low-carbon energy system.” Hultman, who is also a fellow at the Brookings Institution, was not associated with the study.

How do technologies measure up?

According to Trancik, the cost and carbon trade-off curve can be applied to any region and any sector over any period of time to evaluate energy technologies against climate goals.  Along with her co-author, MIT master’s student Daniel Cross-Call, she models the period from 2030 to 2050 and specifically studies the U.S. and China’s electricity sectors.

The researchers find that while major demand-side improvements in energy efficiency will buy some time, the U.S. will need to transition at least 70 percent of its energy to carbon-free technologies by 2050 – even if energy demand is low and the emissions reduction target is high.

Demand-side changes buy more time in China. Efficiency, combined with less stringent emissions allocations, allows for one to two more decades of time to transition to carbon-free technologies. During this time, technologies are expected to improve.

This technology focused perspective, Trancik says, “may help developed and developing countries move past the current impasse in climate negotiations.”

While reaching climate goals is a seemingly formidable task, Trancik says that considering changes to technology performance over time is important. When comparing historical changes in technologies to the future changes needed to meet climate targets, the results paint an optimistic picture.

“Past changes in the cost and carbon curve are comparable to the future changes required to reach carbon intensity targets,” Trancik says. “Along both the cost and carbon axes there is a technology that has changed in the past as much as, or more than, the change needed in the future to reach the carbon intensity and associated cost targets. This is good news.”

The research was partially funded by the MIT Energy Initiative.

May 30, 2013
Vicki Ekstrom, MIT Energy Initiative

In the past decade, the massive expansion of China’s production and export of silicon photovoltaic (PV) cells and panels has cratered the price of those items globally, creating tension between China and the United States, and, more recently, China and the European Union. In a new study (see PDF), MIT researchers explain why these tensions could harm the broader solar industry and have spiraling effects for China-U.S. trade relations.

“China and the U.S., and China and the E.U., are in the midst of a blame game as the solar industry is on the brink of collapse — and the tensions could infect technology and commercial development globally,” says John Deutch, the lead author of the study and Institute Professor at MIT. “All the players should understand that the PV industry is globally linked, and jobs and profits are available for those who manufacture and for those who innovate. Given the complex but productive relationships, nations need to find a way to better work together rather than flirt with protectionist measures.”

Over the last decade, manufacturing of PV cells and panels expanded in China, boosting supply globally. The flood of solar panels, combined with a slipping subsidized demand for solar energy (especially in Europe), lowered the global market price to unsustainable levels, the study shows. Between 2009 and 2012, the price of crystalline silicon panels decreased from more than $2.50 per watt to less than $1 per watt, as China supplied 30 to 50 percent of U.S. PV imports.

The result? PV manufacturers globally haven’t been able to compete, Deutch and the study’s co-author, MIT professor of political science Edward Steinfeld, explain. In response, the U.S. Department of Commerce and the International Trade Commission imposed substantial anti-dumping duties — tariffs imposed on low-priced foreign imports — on some Chinese manufacturers last November, following complaints from U.S. PV manufacturers who alleged that the Chinese were selling their products below fair market value. Around the same time, Europe issued an anti-dumping inquiry; it has also threatened to announce tariffs by June 6.

China has responded with its own allegations, also threatening to issue tariffs — this time, on the materials and technology imported to make the panels. Many of those imports come from the United States. China threatens these tariffs as its PV industry also faces trouble, according to the study: Net margins of panel suppliers in China fell to double-digit negative values in 2011 and remain there now, more than a year later. The study reports that Suntech Power Holdings — the largest PV-panel maker in the world — posted a loss of $495 million in 2012. (The company declared bankruptcy at the end of March.)

Deutch and Steinfeld explain that the two nations — China and the United States — are interdependent and form a “potentially productive global ecosystem for innovation.” When one side declines — as is happening in China, with its PV manufacturers — so will the other side, as is happening in the United States, with its technology and manufacturing tools, the study says. The researchers explain that there are opportunities for the two nations to together accelerate the worldwide deployment of solar PV for electricity generation.

“The two countries have different strengths and weaknesses,” Deutch says. “The U.S. is creating the technology and manufacturing tools and China is successfully, but not profitably, manufacturing devices based on today’s technology. If both countries look at the big picture, choose to focus on their strengths, and put aside the blame game, they have a real opportunity to boost global deployment of solar.”

Arun Majumdar, the vice president for energy at Google and former director of the Department of Energy’s Advanced Research Projects Agency-Energy, says, “Deutch and Steinfeld’s factual and data-driven analysis shows that in the interdependent global market and supply chain of the solar industry, policies of individual governments that foster and leverage their domestic strengths to openly and fairly compete in the global market are better off in the long term to reach national goals of economic growth.”

Majumdar adds, “On the other hand, policies that distort the market via undue protectionism or disproportional investments to reach national goals could backfire and produce opposite outcomes.”

The study will become part of a larger report on the “Future of Solar,” to be released by the MIT Energy Initiative at a later date.

Researchers explore possible consequences of greater biofuel use

The growing global demand for energy, combined with a need to reduce emissions and lessen the effects of climate change, has increased focus on cleaner energy sources. But what unintended consequences could these cleaner sources have on the changing climate?


Researchers at MIT now have some answers to that question, using biofuels as a test case. Their study, recently released in Geophysical Research Letters, found that land-use changes caused by a major ramp-up in biofuel crops — enough to meet about 10 percent of the world’s energy needs — could make some regions even warmer.

“Because all actions have consequences, it’s important to consider that even well-intentioned actions can have unintended negative consequences,” says Willow Hallgren, the lead author of the study and a research associate at MIT’s Joint Program on the Science and Policy of Global Change. “It’s easy to look at a new, cleaner energy source, see how it will directly improve the climate, and stop there without ever considering all the ramifications. But when attempting to mitigate climate change, there’s more to consider than simply substituting out fossil fuels for a cleaner source of energy.”

Hallgren and her colleagues explored some of those consequences in considering two scenarios: one where more forests are cleared to grow biofuel crops, and one where forests are maintained and cropland productivity is intensified through the use of fertilizers and irrigation.

In both cases, the researchers found that at a global scale, greenhouse-gas emissions increase — in the form of more carbon dioxide when CO₂-absorbing forests are cut, and in the form of more nitrous oxide from fertilizers when land use is intensified. But this global warming is counterbalanced when the additional cropland reflects more sunlight, causing some cooling. Additionally, an increase in biofuels would replace some fossil fuel-based energy sources, further countering the warming.

While the effects of large-scale expansion of biofuels seem to cancel each other out globally, the study does point to significant regional impacts — in some cases, far from where the biofuel crops are grown. In the tropics, for example, clearing of rainforests would likely dry the climate and cause warming, with the Amazon Basin and central Africa potentially warming by 1.5 degrees Celsius.

This tropical warming is made worse with more deforestation, which also causes a release of carbon dioxide, further contributing to the warming of the planet. Meanwhile, Arctic regions might generally experience cooling caused by an increase in reflectivity from deforestation.

“Emphasizing changes not only globally, but also regionally, is vitally important when considering the impacts of future energy sources,” Hallgren says. “We’ve found the greatest impacts occur at a regional level.”

From these results, the researchers found that land-use policies that permit more extensive deforestation would have a larger impact on regional emissions and temperatures. Policies that protect forests would likely provide more tolerable future environmental conditions, especially in the tropics.

David McGuire, Professor of Ecology at University of Alaska Fairbanks, says these findings are important for those trying to implement mitigation policies to consider.

“Hallgren et al. caution that society needs to further consider how biofuels policies influence ecosystem services to society as understanding the full dimension of these effects should be taken into consideration before deciding on policies that lead to the implementation of biofuels programs,” McGuire says.

He finds Hallgren’s incorporation of reflectivity and energy feedbacks unique compared to similar studies on the climate impacts of biofuels.

Beyond the climate

While Hallgren focuses specifically on the climate implications of expanded use of biofuels, she admits there are many other possible consequences — such as impacts on food supplies and prices.

A group of her colleagues explored the economic side of biofuel expansion as part of a study released last year in Environmental Science & Technology — a paper that was recognized as that journal’s Best Policy Analysis Paper of 2012.

The team, led by Joint Program on Global Change co-director John Reilly, modeled feedbacks among the atmosphere, ecosystems and the global economy. They found that the combination of a carbon tax, incentives for reforestation and the addition of biofuels could nearly stabilize the climate by the end of the century; increased biofuels production alone could cut fossil-fuel use in half by 2100.

But just as Hallgren found trade-offs when she dug deeper, so did Reilly and his team of researchers.

“The environmental change avoided by reducing greenhouse-gas emissions is substantial and actually means less land used for crops,” Reilly says. This leads to substantial rises in food and forestry prices, he says, with food prices possibly rising by more than 80 percent.

Hallgren says, “There is clearly no one simple cause and effect when it comes to our climate. The impacts we see — both to the environment and the economy — from adding a large supply of biofuels to our energy system illustrate why it is so important to consider all factors so that we’ll know what we’re heading into before making a change.”

Earth Day talk details Massachusetts’ accomplishments since the governor’s MIT speech five years ago, and outlines new goals.