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Archive for August, 2011

World Food Production: Don’t Delude Yourself; Population Will Grow

by August 31, 2011

The following letter-to-the-Editor, a follow-up to my post about global population growth that is essentially a foregone conclusion, appeared in the Aug. 31, 2011 issue of the Minneapolis St. Paul Star Tribune:

In response to Prof. Allen Levine’s commentary about world hunger (“It’s world hunger (and it’s our world,)” Aug. 21), one letter writer and several readers who commented online argue for population control as an essential part of the equation.

In reality, fertility rates have dropped markedly over past decades. Demographers understand that, even at today’s relatively low rates, today’s children will have children of their own faster than older generations will die off.

An aggressive program to lower fertility rates will not alter that reality.

For those concerned about feeding, clothing and fueling the world’s population, accepting that we will have another 3 billion residents on the planet by 2050 is essential.

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In Terms of Indoor Air Conditioning, How Cool is Too Cool?

by August 30, 2011

An article in Sunday’s New York Times by Elisabeth Rosenthal (Oh, to Be Warm in Summer’s Heat) reinforced the notion that some not-so-painful behavioral changes might lead to significant energy (and cost) savings. Yet, we may not be empowered with good information to help us connect the dots. Rosenthal zeros in on our exuberance to crank up the air conditioning in stores and other public spaces like airports. It does seem rather silly that we often need to grab a sweatshirt before heading out, knowing that we’re libel to run into chilly indoor environments.

I’m reminded of an NPR story from yesterday (Summer Sounds: Air Conditioning). It is a story by Teller (of the stage duo Penn & Teller) recounting his solution to the noisy air conditioning unit in his room. His parents had bestowed the unit to him because they knew that his upstairs room would be hotter than their downstairs bedroom. Even though his parents’ sleep was fitful, he solved the on-and-off noise of the A/C unit by turning on the “constant cool” feature, meaning that his room turned into the Arctic, and he needed to bundle up like on a winter’s night…

Back to Rosenthal’s story. She highlights an experience many have no doubt had: the rush of cool air that pours out the open front doors of many retailers. I often joke that they’re fighting a losing battle if their goal is to cool off outside. Of course, their goal is to lure us into the cool indoors, where we’ll want to stay and buy their merchandise.

I wonder if retailers have the information they need to weigh the benefit (extra business) against the cost (inefficient cooling system). Maybe they’d get a boost in consumer traffic if they kept the doors closed and used a marketing campaign advertising their responsible energy plan. Perhaps they could add some low-energy cooling fans near doorways to give pedestrians a sample of the coolness that awaits just inside the (closed) doors. This is clearly a ripe issue for attention, as a quick online search reveals considerable space devoted to this “open door policy” of retailers (here’s a Washington Post article about how the energy-conscious are upset by open doors, and another NY Times post about an informal survey of open doors after NY City banned the policy, albeit with plenty of loop holes for cool air to pour through!).

As discussed in a previous post, we do not do very well estimating the relative energy use of different appliances, such as window versus central A/C units. Similarly, we do not do a good job at predicting the energy savings from various behavioral changes, like adjusting our home thermostat to make it a bit cooler during the winter and a bit warmer during the summer. This blurb and accompanying graph of the typical energy usage in a home from the Energy Star website sums up why we should all pay attention in this time of ever-increasing energy costs:

As much as half of the energy used in your home goes to heating and cooling. So making smart decisions about your home’s heating, ventilating, and air conditioning (HVAC) system can have a big effect on your utility bills – and your comfort.


A final note has to do with a statistic that Rosenthal cited in her article:

Many energy experts recommend setting thermostats at 78 degrees in summer, to conserve energy and to combat rising greenhouse gas emissions. The exact energy savings depends on numerous factors, including the type of air-conditioning and the temperature outside. But turning up the programmable thermostat of a central air-conditioning system 1 degree can yield a 6 percent savings in energy used for cooling, according to the United States Energy Star program.

We’ll need to get to the bottom of the potential savings, which undoubtedly vary regionally and across different types of home construction. The 6-percent-savings is higher than I’ve seen elsewhere, and it seems like a lot for adjusting the thermostat by only a single degree.

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Population Control Should Not Be A Priority Issue for Those Concerned About the Global Food Challenge

by August 29, 2011

In a letter-to-the-editor in today’s Star Tribune, a reader took issue with U of Minnesota Prof. Allen Levine’s recent opinion piece about the challenges facing our global agricultural system. Specifically, the writer asks why Prof. Levine apparently ducked the issue of “population control”:

Prof. Allen Levine makes a number of compelling points about combating world hunger (“It’s world hunger (and it’s our world),” Aug. 21). However, he neglects a key point — because it is our world. He does not mention population control. The fewer people there are, the fewer resources will be used, even with a growing middle class. Why is it anathema these days to talk about population control?

Prof. Levine’s piece raises a number of interesting points and sparked a number of online comments, including several others addressing population control:

  • NO mention of population control in this article? Sure, it’s a thorny issue – but if we don’t find a way to slow population growth, nature will do it for us, as horrific famines! The April, 2011 issue of Wired magazine has a great article about an Indian scientist who has come up with a male birth control method. It’s an inexpensive, easily reversible, safe kind of vasectomy, with zero side effects. The Bill and Melinda Gates Foundation has given this scientist a small grant to pursue this potentially huge solution, so please go to and read about this exciting development!
  • If we don’t find a way to slow population growth, nature will do it for us” Starvation in Africa is an example that it is already occurring.
  • Simple answer: Population control. Remember the 70′s. With less people we will need less fuel, less food, less of everything. Of course that would require responsibility by large population groups. Let’s see which groups responded to this crisis over 40 years ago. Ah! The European and North American groups self regulated their population successfully. The Chinese started later and used coercion. The others…nothing. Time to pull up the drawbridge and stop saving the overpopulators.

As discussed in a previous post chronicling a talk by Hans Rosling, a professor of global health at Sweden’s Karolinska Institute, there’s a lot of momentum in global population trends, and there is really very little that can be done to influence population trends over the next 40-50 years. Baring some unforeseen calamity, demographers predict that the World’s population will reach 9 billion by 2050, a statistic cited by Prof. Levine. The reason is that today’s children will have their own children faster than older generations will die off. This is true even with the low fertility rates existing across most of the planet. (more…)

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GPM Sheds Light On Why Hybrid Cars Are Tough To Justify On Fuel Savings Alone

by August 23, 2011

Hybrid car parking only

Photo credit, Chris Bloke on Flickr

Have you ever considered buying a hybrid car and gone through the calculations to compare the fuel cost savings to the higher price over comparable non-hybrid models? Chances are good that the math is not on the side of purchasing a hybrid, as pointed out in this USA Today opinion piece questioning the recently-announced, aggressive fuel efficiency standards. Most likely, it is our choice of metrics for evaluating fuel efficiency that help to make such calculations turn out to be less intuitive than we might expect, as discussed in this previous post on fuel economy metrics.

Hybrid cars are those that combine a large battery with an engine that generally runs on gasoline, although diesel hybrids are possible. In city driving with lots of starts and stops, the energy normally lost through braking is used to incrementally charge the battery—through a technology known as regenerative braking. If you’re looking for a 2-minute diversion, check out this video below featuring Maxwell von Stein, whose video was featured on Science Friday last week. He created a bike that uses a flywheel to store energy from braking to provide a boost literally down-the-road. He sees this as a great test case for creating a new type of hybrid car…

Because we need to brake less on highways, hybrids lose much of their advantage during highway driving. You can check out the EPA city/highway ratings for hybrids and compare them to non-hybrids side-by-side at

Following up on the previous post on MPG v. GPM (that is, miles per gallon v. gallons per mile), here are some quick calculations showing the fuel savings for two models from Toyota (Camry) and Ford (Fusion) that are available as hybrids. As in the previous post, the orange bar shows the fuel savings in gallons for 5000 miles of city driving.


The Fusion Hybrid driver could anticipate saving about $1000 on fuel over three years if she/he drove 5000 city miles, and the Camry Hybrid driver could expect about $700 in savings for three years of 5000 city miles—these calculations assume a gas price of $3.50 per gallon.

Grabbing some rough prices from Motor Trend’s site, it would cost about $6800 more for a Fusion Hybrid and about $4400 for a Camry Hybrid (these comparisons are very rough and are based on models that are one step up from the base offering for the non-hybrids; they also do not include any applicable rebates, deals, etc.).

Baring any government subsidy to help offset the purchase price, we immediately see the quandary facing a potential purchaser of a hybrid car: it is very tough to imagine recovering the extra purchase price through fuel cost savings. Plus, as mentioned above, if the hybrid was to be used for a good bit of highway driving, the potential fuel savings would diminish considerably.

I argued in the aforementioned post that GPM is a better way to get an intuitive feel for fuel savings. Interestingly the site offers vehicle stats in GPM rather than MPG. I have to wonder if many people click on that option. Here are the side-by-side comparisons of the hybrid and non-hybrid Fusion and Camry models. First, using MPG as the comparison point, then with gallons per hundred miles (GPM). The cost savings tables at the bottom provide the same type of thought experiment as described above, though it is a bit more complex blending highway and city mileage.

fueleconomy_gov_mpg fueleconomy_gov_gpm

It would be a little like getting a nation to think metric, but one gets a sense that the second comparison provides information that is more instructive about cost savings from fuel usage.

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How Would Smiley Faces Change My Driving Behavior?

by August 12, 2011

xcelenergyreport1 Having just spent a bunch of time working on a pre-proposal for the National Science Foundation, I’m excited about an idea to create more feedback for drivers about their energy use. This project concept is motivated by recent research that many of us have a tough time judging the relative energy savings from a variety of behavior changes.

For example, the researchers found that many Americans estimate that a central air conditioning system uses about the same amount of energy as a window unit, when in fact a window unit typically uses several times less energy (link to abstract of article by Shahzeen Z. Attari and colleagues in the Proceedings of the National Academy of Sciences here).

Perhaps you are an Xcel Energy customer, or you’re with another utility that is taking advantage of OPOWER’s innovative approach to giving feedback to utility customers. As a residential customer of Xcel’s, we receive a monthly statement showing our use of energy compared to similarly-sized homes in our neighborhood. Thus, we receive a chart with our use of electricity and natural gas over the past 12 months, comparing our usage to that of our “efficient neighbors” and “all neighbors.” Here is our household usage over the past year from Xcel’s Energy Report website, which provides all of the data digitally after registering. (more…)

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Do Electric Cars and Nuclear Power Really Have Zero Carbon Emissions?

by August 8, 2011

The Nissan Leaf

Photo credit, Tom Raftery on Flickr

A piece about incentives to promote electric cars in Europe published in the Star Tribune a few days caught my eye. The author, who actually wrote the piece for the New York Times, discusses how the size of incentives are linked with reductions in carbon emissions and stated “Logically, electric cars with zero carbon emissions qualify for the largest incentives.”

Unless the electric vehicle (EV) was manufactured in world that uses no carbon-based fuels and the electricity that charges the EV’s batteries is devoid of carbon emissions, then this is not possible.

My guess is that the author confused direct and indirect emissions from EVs. Yes, there are no carbon emissions from EVs directly. However, electricity is needed to charge an EV’s battery, and even wind and solar have small carbon emissions. Electric vehicles also need to be manufactured and maintained, both of which will contribute to lifecycle emissions of carbon. Here’s one recent study that digs into the the energy use, cost, and carbon dioxide emissions of electric cars.

The statement about EVs reminded me of similar statements I’ve heard recently on the radio about nuclear energy. True, the plume that is characteristic of a nuclear plant’s cooling towers is water vapor. Yet, there are considerable lifecycle emissions of carbon connected to facility construction, uranium mining and processing, and waste disposal. Here’s a recent paper that evaluates the lifecycle emissions associated with nuclear energy, including estimates of how nuclear compares to other energy sources—on average about twice that of solar photovoltaic (PV) and about seven times less than natural gas.

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Using Miles Per Gallon Ratings To Reduce A Nation’s Oil Consumption Is An Indirect Approach

by August 2, 2011


AP Video Coverage of President Obama's Announcement

The new agreement between President Obama and automakers, nearly doubling fuel efficiency for automobiles by 2025, will have a direct impact on oil consumption by the U.S. automobile fleet. Yet, if this aggressive goal is fueled by a desire to maximize reductions in oil consumption, then it would be more useful to measure our performance with a direct indicator of oil consumption: gallons per mile (GPM), the inverse of our standard metric, miles per gallon (MPG). (more…)

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