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New analysis of population trends and their impact on global greenhouse gas emissions

Tuesday, October 12th, 2010

In 40 years, there will be about 3 billion additional people living on the Earth (~9.5 billion total).   With all of these new folks, it’s easy to think about the added demands of energy, food, and water required to sustain their lifestyles.  And in terms of climate warming, it’s hard to escape the fact that significantly greater energy consumption will lead to rising rates of carbon emissions, unless there’s a shift to decarbonize the economy.

In this week’s early Edition of the Proceedings of the National Academy of Sciences (open access), Brian O’Neill and colleagues note that emissions are not just controlled by the sheer size of the human population but also by important demographic changes.

For example, how might an aging or more urban population affect emissions?  How about changes in household size?  Modelers of carbon emissions don’t usually ask these kinds of questions, so the conventionally projected emissions might be off if these additional demographic details matter.

The researchers developed a global economic model (Population-Environment-Technology, or PET) in which they specified relationships between demographic factors like houshold size, age, and urban/rural residency and economic factors like the demand for consumer goods, wealth, and the supply of labor.  Here’s a bit more on how this works:

In the PET model, households can affect emissions either directly through their consumption patterns or indirectly through their effects on economic growth in ways that up until now have not been explicitly accounted for in emissions models. The direct effect on emissions is represented by disaggregating household consumption for each household type into four categories of goods (energy, food, transport, and other) so that shifts in the composition of the population by household type produce shifts in the aggregate mix of goods demanded. Because different goods have different energy intensities of production, these shifts can lead to changes in emissions rates. To represent indirect effects on emissions through economic growth, the PET model
explicitly accounts for the effect of (i) population growth rates on economic growth rates, (ii) age structure changes on labor supply, (iii) urbanization on labor productivity, and (iv) anticipated demographic change (and its economic effects) on savings and consumption behavior.

Although there are some exceptions, households that are older, larger, or more rural tend to have lower per capita labor supply than those that are younger, smaller, or more urban. Lower-income households (e.g., rural households in developing countries) spend a larger share of income on food and a smaller share on transportation than higher-income households. Although labor supply and preferences can be influenced by a range of nondemographic factors, our scenarios focus on capturing the effects of shifts in population across types of households.

To project these demographic trends, we use the high, medium, and low scenarios of the United Nations (UN) 2003 Long-Range World Population Projections combined with the UN 2007 Urbanization Prospects extended by the International Institute for Applied Systems Analysis (IIASA) and derive population by age, sex, and rural/urban residence for the period of 2000–2100.

What did they find?


Posted in behavior, climate economics, energy, gender, population, sustainability, urban | No Comments »

What’s the carbon footprint of building your car, and how does that compare to tailpipe emissions?

Friday, September 24th, 2010

Mike Berners-Lee and Duncan Clark at The Guardian have a recent post in the series examining the carbon footprints of daily life activities.  Their post asks how much carbon emissions results from the direct and indirect activities of building a car.

The carbon footprint of making a car is immensely complex. Ores have to be dug out of the ground and the metals extracted. These have to be turned into parts. Other components have to be brought together: rubber tyres, plastic dashboards, paint, and so on. All of this involves transporting things around the world. The whole lot then has to be assembled, and every stage in the process requires energy. The companies that make cars have offices and other infrastructure with their own carbon footprints, which we need to somehow allocate proportionately to the cars that are made.

….The best we can do is use so-called input-output analysis to break up the known total emissions of the world or a country into different industries and sectors, in the process taking account of how each industry consumes the goods and services of all the others. If we do this, and then divide by the total emissions of the auto industry by the total amount of money spent on new cars, we reach a footprint of 720kg CO2e per £1000 spent.

This is only a guideline figure, of course, as some cars may be more efficiently produced than others of the same price. But it’s a reasonable ballpark estimate, and it suggests that cars have much bigger footprints than is traditionally believed. Producing a medium-sized new car costing £24,000 may generate more than 17 tonnes of CO2e – almost as much as three years’ worth of gas and electricity in the typical UK home.

17 (metric) tons is 17,000 kg or about 37,400 pounds.   The U.S. EPA estimates that the average passenger vehicle in the U.S. emits 5-5.5 metric tons CO2e per year, assuming 12,000 miles driven.

If you do the math, this means the embodied CO2e emissions to make a car is about 3-3.5 years worth of tailpipe emissions from driving.  Assuming that most people own their cars for longer than three years, this figure doesn’t jive with what the authors claim:

The upshot is that – despite common claims to contrary – the embodied emissions of a car typically rival the exhaust pipe emissions over its entire lifetime. Indeed, for each mile driven, the emissions from the manufacture of a top-of-the-range Land Rover Discovery that ends up being scrapped after 100,000 miles may be as much as four times higher than the tailpipe emissions of a Citroen C1.

If people held onto their cars for 10 years (assuming 120,000 miles), tailpipe emissions would equal 50 metric tons of CO2e, and embodied emissions would be about 34% of tailpipe emissions.  If people drove their cars for 20 years (assuming 240,000 miles), the exhaust emissions would rise to 100 metric tons CO2e, with embodied emissions dropping to 17% of tailpipe emissions.

While most folks generally agree with the notion of driving their vehicle into the ground (as my recently dead 16-yr-old truck illustrates), you’d have to be driving a Toyota Prius to get a lifetime tailpipe emission that equals the embodied emissions of building it (assuming that a Prius achieves three times the mpg of a typical car, which would drop CO2e tailpipe emissions from 5 to 1.7 metric tons CO2e per year, making a 10-year total tailpipe emission of 17 metric tons reasonable).

Thus, if you drive an average car for 10 years, your lifetime tailpipe emissions (50 metric tons) will be a lot larger than the embodied emissions to build the car (17 metric tons) (for a total emission of 67 metric tons).  If you drive a hyper-efficient vehicle for 10 years, tailpipe and embodied emissions may be comparable (17 metric tons each, 34 metric tons total).  This means you could buy a new Prius every three years, and the embodied emissions from all of these purchases plus tailpipe emissions would roughly equal a normal car driven for 10 years.

This raises an important question:  What matters here?  If the goal is to reduce total emissions, the best thing is to buy a car with a very high fuel efficiency and drive it for its full life, as the above examples illustrate.


Photo credit:  atomicshark

Posted in behavior, carbon footprint, climate change science, energy, solutions, sustainability, technology, transportation | 3 Comments »

Homes of the future?

Saturday, September 11th, 2010

The NYT is running an op-ed by Bob Dunay and Joseph Wheeler (Virginia Tech) about a new, award-winning home design that challenges people to re-think their conception of the built environment:

Will our children’s homes be anything as comfortable and expansive as our own?

The answer is yes—though it depends on how you frame the question. Our children probably won’t be able to afford to run conventional air conditioners all day long. Nor will they likely have access to unlimited water supplies, particularly in the parched Southwest. But that doesn’t mean they have to live without the same quality of life that their parents and grandparents have grown accustomed to. The key is to use smart planning and technological advances to not merely adapt the home, but rethink its most basic design and function.

To demonstrate what such a house might look like, our team of professors and students at Virginia Tech designed and built Lumenhaus. With functional spaces and a modest size that allows for efficient energy use, Lumenhaus won the 2010 Solar Decathlon Europe, a competition that brought together 17 college teams from around the world in Madrid.

Check out the film about this house and the interesting interactive feature.

Posted in nature and culture, solutions, sustainability, sustainable architecture, technology | No Comments »

Rethinking personal transportation in small towns

Sunday, September 5th, 2010

Mitigating climate warming is going to require a dramatic decrease in carbon emission from the transportation sector, through a combination of driving less, using public transportation, and, eventually, switching to electric cars powered by a renewable grid.

There are many urban centers with outstanding public transportation options, but let’s face it— It’s often more difficult to find alternatives to driving in smaller towns and suburbs.

Brunswick, Maine (home to Bowdoin College) is no different than most small towns (population 25,000).  Transportation is one of the largest sources of carbon emissions, and the physical dislocation of residential areas, shopping centers, supermarkets, and hospitals makes it difficult to avoid automobile use.  And roads around here are definitely not bike friendly!

This is starting to change as a result of collaborations across institutions from the local to federal levels.

The town just added a new program called Brunswick Explorer, with a fleet of hybrid electric buses that are wheelchair and bike accessible.  The route takes the buses from major residential areas (especially those serving the elderly) to our local supermarkets, hospitals, and shopping malls.

With the extension of the Amtrak Downeaster from Portland to Brunswick in 2012, folks will also be able to travel to Portland and Boston easily by train, especially during rush hour and winter when travel by roads is either a hassle or dangerous.

The Explorer and Downeaster are certainly no silver bullets, but they accomplish a few important goals:

  • The Explorer allows people in much of downtown Brunswick the opportunity to forego driving for simple, routine tasks, especially during winter when walking and biking are treacherous.
  • The hybrid fleet and high-occupancy vehicles will help reduce emissions.
  • Reliable bus service makes it easier for families (who are able) to downsize from two vehicles to one vehicle, with the added benefit/incentive of saving on gas, repairs, taxes, registration, and inspections.
  • At a cost of $1 per ride or $2 for an all-day pass, the Explorer buses provide an important social service to the elderly and other citizens who may not be able to afford cars.
  • It builds transportation resilience in the community, especially for low-income citizens who may find it increasingly expensive to get around the next time gas prices spike.
  • The Downeaster provides a redundant transportation network, which makes long-distance travel easy when there are unexpected travel delays due to weather, construction, or accidents.  It also has the potential to take many cars off the road for the sizable population that commutes daily between Portland and Brunswick.
  • The Explorer bus program provides a model of community collaboration that may be exportable to other towns.
  • Perhaps most importantly, they help break the mindset and habits of routine personal vehicle use.

These are small steps, indeed, but they have the ingredients to be successful:  alternatives to personal vehicle use that are both cheap and convenient, with substantial community buy in.


Photo courtesy of Bowdoin College

Posted in behavior, campus sustainability, energy, race and class, solutions, sustainability, transportation | 1 Comment »

Will the Gulf spill be a catalyst for change?

Saturday, June 12th, 2010

In Tom Friedman’s column in the Sunday NY Times, he describes a poignant letter written by a friend in the Pentagon to his hometown South Carolina newspaper:

“I’d like to join in on the blame game that has come to define our national approach to the ongoing environmental disaster in the Gulf of Mexico. This isn’t BP’s or Transocean’s fault. It’s not the government’s fault. It’s my fault. I’m the one to blame and I’m sorry. It’s my fault because I haven’t digested the world’s in-your-face hints that maybe I ought to think about the future and change the unsustainable way I live my life. If the geopolitical, economic, and technological shifts of the 1990s didn’t do it; if the terrorist attacks of Sept. 11 didn’t do it; if the current economic crisis didn’t do it; perhaps this oil spill will be the catalyst for me, as a citizen, to wean myself off of my petroleum-based lifestyle. ‘Citizen’ is the key word. It’s what we do as individuals that count. For those on the left, government regulation will not solve this problem. Government’s role should be to create an environment of opportunity that taps into the innovation and entrepreneurialism that define us as Americans. For those on the right, if you want less government and taxes, then decide what you’ll give up and what you’ll contribute. Here’s the bottom line: If we want to end our oil addiction, we, as citizens, need to pony up: bike to work, plant a garden, do something. So again, the oil spill is my fault. I’m sorry. I haven’t done my part. Now I have to convince my wife to give up her S.U.V.”

Read the rest of the column here.

And the photo above is a bicycle parking garage in Amsterdam.  Here’s a cool rendition of a recently proposed bike station in Philadelphia that could replace a 100-car lot with a 690-bike garage.  If fully utilized, and assuming single-occupancy commutes, this could generate up to a 7-fold reduction in vehicle use.  One good idea in a suite of many that will be needed.


Photo credit:

Posted in behavior, energy, nature and culture, solutions, sustainability | No Comments »

City dwellers of the future: Urban heat island warming may be as large as doubling CO2

Monday, April 19th, 2010

I remember driving on a freeway in Phoenix after midnight in 1990.  The temperature was a cool 102 degrees F after breaking the all-time heat record of 126 F that day.  Deserts are good at cooling off at night.  But with all of the built environment in Phoenix storing heat from the day, the sidewalks, roads, and even swimming pools felt like they were being heated.

We all have probably experienced urban heat islands—the mass of dark asphalt and concrete absorbing solar radiation and radiating it back to space as heat.  The lack of water exacerbates the situation because there is little-to-no evaporative cooling.  Waste heat from cars, machines, air conditioners, and even human bodies also heat up the air.  And the warmer it gets, the stronger the tendency to crank up the air conditioners, generating even more waste heat.

The problem is potentially large in areas like the Middle East, India, parts of Africa, and the American Southwest, where rapid urbanization in warm, dry environments has the potential to make some urban areas much warmer at night than surrounding rural areas.

In a forthcoming article in Geophysical Research Letters1, Mark McCarthy and colleagues at the Met Office, Hadley Centre, UK used a climate model that examines what climate might look like in a doubled CO2 world and calculates the added warming caused by urbanization and wasted heat.

Their results were eye-opening:

  • Urban regions in places like the Arabian Peninsula, Iran, and India may experience night time warming by as much as 3-5 degrees C above and beyond that caused by doubled CO2 alone.
  • The number of hot nights per year (defined as temperatures in the 99th percentile of nonurban areas) increase in the following cities:
    • London: 1-2 hot nights now vs. up to 10 hot nights in 2050
    • Sydney: 1-2 hot nights now vs. up to 15 hot nights in 2050
    • Delhi: 5-10 hot nights now vs. up to 30 hot nights in 2050
    • Beijing: 3-6 hot nights now vs. up to 50 hot nights in 2050
    • Los Angeles: 8-12 hot nights now vs. up to 40 hot nights in 2050
    • Tehran: 20 hot nights now vs. up to 60 hot nights in 2050
    • Sao Paulo: <5 hot nights now vs. up to 80 hot nights in 2050
    • Lagos (Nigeria): <5 hot nights now vs. up to 150 hot nights in 2050

As mentioned in an earlier post, we only need to remember Chicago in 1995 to recall the deadly impact that heat waves can have on urban people.  And as we saw in that unfortunate example, the victims were disproportionately the elderly and African American.

Although we may not be able to mitigate this warming, basic adaptation steps should be set into motion, including re-thinking urban design, making cities more resilient to hot environments, developing better energy and technology solutions (including cooling), installing green roofs, and putting into place emergency disaster plans and social safety nets for vulnerable populations.

1Mark McCarthy, Martin Best, and Richard Betts (2010). Climate change in cities due to global warming and urban effects Geophysical Research Letters : 10.1029/2010GL042845

Photo Credit: / CC BY-NC-ND 2.0

Posted in climate adaptation, climate change science, energy, environmental justice, health, land use, population, race and class, sustainability, technology, urban | 3 Comments »

This week’s good ideas in campus sustainability: 3/29/10

Monday, March 29th, 2010

AASHE is showcasing the new American College & University Presidents’ Climate Commitment (ACUPCC) 2009 report, which highlights climate leadership in higher education.

The Report includes highlights from 2009; a list of innovative ways schools are applying their Climate Action Plans to areas such as curriculum, transportation, renewable energy, and partnerships within and outside the campus gates; a description of the impact the Commitment has had on the reduction of carbon emissions; information on the Climate Action Plans that have been submitted; a list of resources available to signatory institutions; and the ACUPCC budget. The ACUPCC, launched in early 2007, is currently comprised of 677 schools in all 50 states and the District of Columbia – representing nearly six million students and about one third of the US higher education student population.

Link to story

Link to the ACUPCC report (pdf)


More information:  AASHE bulletin 3/29/10

Posted in campus sustainability, higher education, solutions, sustainability | No Comments »

Stavins: “What’s the Proper Role of Individuals and Institutions in Addressing Climate Change?”

Saturday, March 13th, 2010

That’s the question asked by Robert Stavins at Harvard.  This piece is worth reading.  He wrestles with many of the same questions that many of us in higher education have thought a lot about (here, here, here, and here):

My view of a university’s responsibilities in the environmental realm is similar.  Our direct impact on the natural environment — such as in terms of CO2 emissions from our heating plants — is absolutely trivial compared with the impacts on the environment (including climate change) of our products:  knowledge produced through research, informed students produced through our teaching, and outreach to the policy world carried out by faculty.

So, I suggested to the students that if they were really concerned with how the university affects climate change, then their greatest attention should be given to priorities and performance in the realms of teaching, research, and outreach.

Of course, it is also true that work on the “greening of the university” can in some cases play a relevant role in research and teaching.  And, more broadly — and more importantly — the university’s actions in regard to its “carbon footprint” can have symbolic value.  And symbolic actions — even when they mean little in terms of real, direct impacts — can have effects in the larger political world.  This is particularly true in the case of a prominent university, such as my own.

But, overall, my institution’s greatest opportunity — indeed, its greatest responsibility — with regard to addressing global climate change is and will be through its research, teaching, and outreach to the policy community.

Although I applaud the call for more emphasis on environmental teaching and the addition of environmental courses, several impediments exist in higher education and beyond which make it difficult to translate these actions into a more environmentally literate society:

  • Disciplines, departments, and majors have long been divided into separate silos.  We reward specialization and expertise over the kinds of interdisciplinarity that is needed to conceive of and deal with global change problems.  As we have seen in previous posts, it’s time for higher education to consider adding problem-centered approaches to the general curriculum.
  • As a result, training students about the environment is often the responsibility of environmental studies and science (ESS) programs.   This is a problem because it absolves most departments and faculty from having to engage the environment as a serious issue.  Many programs at a typical university operate as if humans have little or no connection to the natural world.  Until human systems are properly embedded in natural systems and students are encouraged/required to explore these linkages, there is little reason for students to associate the human experience with impacts on the natural world.
  • These kinds of structures are problematic.   At best, it means that most students in higher education receive little substantive training in how their lives connect with the natural world.  At worst, students are trained to perpetuate disciplinary tradition that (1) ignores the relationship between human societies and the environment and (2) values high achievement in a world that is ecologically unsustainable and socially unjust as a measure of success.
  • There can be limits to a “more knowledge” approach.  Namely, as we have seen with climate communication, cultural values shape the perception/reception of information.  Just as  scientific facts seldom speak for themselves, we can’t expect a push for more education to always solve environmental challenges either.  The way messages are framed is important.  And the cultural context of the target audience is also critical.  Most people in the world have a very different cultural background than Harvard undergraduates.

Posted in behavior, communication and framing, higher education, nature and culture, sustainability | No Comments »

This week’s good ideas in campus sustainability: 3/1/10

Thursday, March 4th, 2010

This week’s showcase features Beloit College, Central College, and Iowa State University.  LEED Platinum is not easy to achieve, and it’s even more impressive with projects this large.

1. Beloit College’s Science Center gets LEED Platinum Nod

“The success of our new science center reflects the phenomenal collaboration of creative architects, talented engineers, professional construction firms and the finest faculty and staff who were, and are, committed to the best outcome for our students,” said Beloit College president Scott Bierman. “We are, of course, thrilled to have gotten LEED platinum status; but even more important is that we have a building that works terrifically well­—as well as any I have ever seen—as an integrated set of learning spaces.”

2.  Central receives platinum LEED rating for new building

“This special recognition from the USGBC brings great joy to the whole Central College community and reflects continuing success of our pursuit of a sustainable future as a long-term goal adopted by Central’s board of trustees,” said Central College President David Roe. “The achievement was made possible through the concerted efforts of the professionals on Central’s staff led by Mike Lubberden and a large team of amazing corporate partners including Weitz Corporation as our general contractor, RDG Planning and Design, MEP and Associates, and Pella Corporation.”

3. ISU’s King Pavilion first education building in Iowa to earn LEED Platinum certification

Located on the north side of the College of Design building, the $6.6 million, 23,735 gross-square-foot King Pavilion features a central, two-story “forum” surrounded by instructional studios used by all freshmen in the college, as well as sophomores in architecture, landscape architecture and interior design. “We are delighted to have the King Pavilion receive LEED Platinum certification,” said ISU President Gregory Geoffroy. “The King Pavilion stands as a testament to the commitment that Iowa State University has made to becoming a model ‘green’ university, in our daily operations as well as in our teaching, research and outreach programs.”

For more information:  AASHE bulletin 3/1/10

Posted in campus sustainability, energy, higher education, solutions, sustainability | No Comments »

Land consumption and open space loss across U.S. cities

Tuesday, March 2nd, 2010

The issue of land use change is a complex, with many factors being important historically, such as

  • population growth (more land required for more people)
  • technology (e.g., automobiles made suburban expansion feasible)
  • economics (cheaper land and rents in suburbs compared to cities)
  • policy (things like 30-yr mortgages, mortgage insurance, and FHA loans had a large impact on urban sprawl because they often made it cheaper to own rather than rent)
  • cultural values (the romanticized notion of a detached home in a safe, pollution-free neighborhood with good schools)

In this week’s PLoS One, Robert McDonald and colleagues1 examined land use change for 274 metro areas (figure 1) in the U.S. to determine tends across cities.

Their results were interesting (excerpts):

  • 1.4 million ha of open space was lost, and the amount lost in a given city was correlated with population growth.
  • American cities vary by more than an order of magnitude in their MSA-wide per capita land consumption. Generally large cities have small per capita land consumption, with the five smallest in 2000 being New York (459 m2/person), Miami (476 m2/person), Philadelphia (519 m2/person), Los Angeles (535 m2/person), and Washington, DC (536 m2/person). Conversely, many small cities have large per capita land consumption, with the five biggest in 2000 being Grand Forks, ND (5394 m2/person), Bismark, ND (3913 m2/person), Flagstaff, AZ (3381 m2/person), Enid, OK (3249 m2/person), and Cheyenne, WY (3073 m2/person).
  • The per capita land consumption (m2/person) of most cities decreased on average over the decade from 1,564 to 1,454 m 2/person, but there was substantial regional variation and some cities even increased.
  • Cities with greater conservation funding or more reform-minded zoning tended to decrease in per capita land consumption (scroll to table 1) more than other cities.
  • The inequality of land consumption varied geographically, with less inequality on the East Coast compared to the West Coast (scroll to figure 4).

They provide a simplified snapshot of how development changes with history and geography (for a more-thorough yet readable treatment of land use in the U.S., check out Crabgrass Frontier by Kenneth Jackson):

The process of development plays out differently in cities with different socioeconomic histories. Moreover, cultural differences exist among and within many U.S. cities, leading to varying spatial patterns of development. However, a general historical pattern exists. In many U.S. cities, an urban core existed in the decades or centuries prior to the widespread use of the automobile, and these neighborhoods have high population density and small amounts of developed area per capita. The surrounding suburban and exurban areas, created predominately after WWII, contain residents living at lower population density and consume more land per capita. There are substantial economic links between these two zones, and in contemporary U.S. cities commuting occurs in both directions. Northeast U.S. cities that developed before the automobile typically follow this narrative. Many have a relatively dense urban core, but have adopted zoning policies that ensure contemporary suburban settlements occur at lower density. While they remain dense compared to other U.S. cities, they are getting less dense over time, as proportionally more of the population is in suburban areas. The declining manufacturing cities of the Rust Belt and the Southern Appalachians are an extreme example of this spreading out of population.

Southeastern U.S. cities, excluding Florida, are often newer and have less of a legacy of a dense urban core. They do not appear to be getting markedly denser, and the relatively fast population growth of these cities implies that their total impact on natural habitat in coming decades will be large. In contrast to the Southeast, Western cities appear to be getting denser, including those that do not have a historical legacy of a dense urban core such as Phoenix. These Western cities are often still growing quickly and consuming a great deal of land, but contemporary development is making these cities denser than they were previously. Many of these Western cities have a strong conservation culture, and the degree of conservation funding and reform-minded zoning correlates with how much denser they are getting. However, it should be noted that contemporary development in Western cities is still well below the densities found in the dense urban core of Northeastern U.S. cities, posing problems for designing effective public transit systems.

1McDonald, R., Forman, R., & Kareiva, P. (2010). Open Space Loss and Land Inequality in United States’ Cities, 1990–2000 PLoS ONE, 5 (3) DOI: 10.1371/journal.pone.0009509


Photo Credit: / CC BY-NC 2.0

Posted in behavior, land use, nature and culture, policy, population, sustainability, transportation, urban | 1 Comment »

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