Monday, November 1st, 2010
An amazing night-time photo from the International Space Station showing how human settlement along the Nile River and Delta stand out against the Sahara Desert (shot by Astronaut Doug Wheelock). Click here for a larger image.
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?
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:
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
Tuesday, March 2nd, 2010
The issue of land use change is a complex, with many factors being important historically, such as
Their results were interesting (excerpts):
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
Wednesday, December 9th, 2009
Let’s face it, how many people have a spare $10k lying around for a new furnace? Not me, and I could use a new furnace.
Home weatherization and efficiency upgrades can make a big difference in U.S. carbon emissions. As we saw in a previous post, American households (including personal transportation) are responsible for
Unfortunately, there’s a big disconnect between things we can do to to save home energy and the ability for folks to pay for these improvements. New insulation, solar hot water, solar photovoltaics, high-efficiency furnaces: Take your pick….Each can cost $10k or more.
Fortunately, there are a lot of creative ideas coming to the rescue to help people defray these up-front costs:
These kinds of programs make a lot of sense and have the potential to be game changers, along with helping Americans transition to electric vehicles as soon as possible.
Monday, November 9th, 2009
Let’s take a look at five innovative and exciting ideas from Stanford University, City College of New York, Western Michigan University, UC-Davis, and the University of Arizona…