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Training the Cloud with the Crowd: Training A Google Prediction API Model Using CrowdFlower’s Workforce

by February 29, 2012



Can a machine be taught to determine the sentiment of a Twitter message about weather?  With the data from over 1 million crowd sourced human judgements the goal was to use this data to train a predictive model and use this machine learning system to make judgements.  Below are the highlights from the research and development of a machine learning model in the cloud that predicts the sentiment of text regarding the weather.  The following are the major technologies used in this research:  Google Prediction APICrowdFlowerTwitter,  Google Maps.

The only person that can really determine the true sentiment of a tweet is the person who wrote it.  When the human crowd worker makes tweet sentiment judgements only 44% of the time do all 5 humans make the same judgement.  CrowdFlower’s crowd sourcing processes are great for managing the art and science of sentiment analysis.  You can scale up CrowdFlower’s number of crowd workers per record to increase accuracy, of course at a scaled up cost.

The results of this study show that when all 5 crowd workers agree on the sentiment of tweet the predictive model makes the same judgement 90% of the time.  When you take all tweets the CrowdFlower and Predictive model return the same judgement 71% of the time.  Both CrowdFlower and Google Predictions supplement rather than substitute each other.  As shown in this study, CrowdFlower can successfully be used to build a domain/niche specific data set to train a Google Prediciton model.  I see the power of integrating machine learning into  crowd sourcing systems like CrowdFlower.  CrowdFlower users could have the option of automatically training a predictive model as the crowd workers make their judgements.  CrowdFlower could continually monitor the models trending accuracy and then progressively include machine workers into the worker pool.  Once the model hit X accuracy you could have a majority of data stream routed to predictive judgments while continuing to feed a small percentage of data the crowd to refresh current topics and continually validate accuracy.  MTurk hits may only be pennies but Google Prediction ‘hits’ cost even less.


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How Do Greenhouse Gases Trap Heat in the Atmosphere?

by February 26, 2012

If you would like to see a high-quality infographic developed for this question, please share it with your network using the sharing icons above—these actions will increase the question’s priority. Please look at the example answers here. Also, if you would value a high-quality answer being available on the Web, please consider a small donation ($0.99) to support our research team.

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What Causes Oxygen to be Used Up In Deep Waters?

by February 26, 2012

ANSWER (CURRENTLY UNDER REVIEW): Bacteria use up the oxygen in the process of breaking down organic matter, like the waste from tiny animals and dead algae. This answer is focused on coastal ocean waters, but generally applies to deep waters in estuaries, ponds, lakes, and slow-moving stretches of rivers.

Q001 how oxygen is used up in deep waters v04

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EarthQ Core Business Model: Where Is the Sweet Spot?

by February 1, 2012

Recently, we have been working to launch a project dubbed EarthQ. The goal has been to shepherd good questions and cultivate good answers by bringing the right mix of experts to Quora, as is described in this post about bringing the carbon cycle to Quora. This work continues, but so far, my attempts to draw in a few experts to help with answers have come up dry. The Quora team thinks it is okay for those who pose a question to answer it, so that will likely be my next step. Perhaps with a solid answer to the first question, What are the compartments in which carbon is stored on Earth?, I can then start to draw in some colleagues to endorse the answer by up-voting it… (more…)

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Tracking the Mood About Gas Prices on Twitter: A Case Study

by January 25, 2012

As another test of our strategy for teasing out public opinion from social media, we explored measuring mood about gas prices on Twitter. This post summarizes the findings from this case study. Incidentally, we are set up to measure mood from Twitter on an ongoing basis, although we would need to find a partner to help defray the ongoing costs of crowdsourcing the sentiment judgments. (See this post to read more about our decision to examine the discussion about gas prices on Twitter.)

The sentiment we mapped was culled from tweets gathered from four weeks’ worth of data starting on May 22nd, 2011. This time period was chosen to coincide with Memorial Day, a holiday during which many Americans travel by car. Our team was curious to see whether there would be an uptick in either the volume of tweets about gas prices during this period or a noticeable change in sentiment about these prices. (more…)

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Monitoring Will Be Key As Minnesota Takes A Leadership Role in Managing Nutrient Runoff

by January 18, 2012

5223892647_2a55e1b7c2 Yesterday I had the opportunity to hear EPA Administrator Lisa Jackson speak at the University of Minnesota, who was in town to launch a new program along with Minnesota’s Governor Mark Dayton and USDA secretary Tom Vilsack. The new initiative, Minnesota Agricultural Water Quality Certification Program, has a goal of reducing the introduction of nutrients and soils to waterways via runoff, a process known as “non-point source pollution” (a point source is a pipe, a sewage treatment plant, etc.).

I was drawn to the talk specifically to hear what Administrator Jackson would say about the new program, which I had read about in the morning’s Minneapolis StarTribune. She did not disappoint, although the bit about this new program occurred just as the questioning period came to a close. It was clear that she has a good deal of enthusiasm about this new program and its prospects for helping to reduce pollution, such as the introduction of nitrogen into the Mississippi that can lead to low-oxygen conditions in the Gulf of Mexico. (more…)

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A Billion Dollars Flowing Down the Mississippi Annually

by December 20, 2011

In a recent post, I did a bit of research to update the picture of nutrient flows down the Mississippi due to runoff and other sources in its watershed. There’s been an ongoing debate about the source of the nutrients in the river that are directly linked to low-oxygen conditions in the Gulf of Mexico.

For a taste of the debate, check out the controversy a year ago surrounding the premier of Troubled Waters, A Mississippi River Story (link to view on Twin Cities Public TV). Among other activity, there was a heated back-and-forth on the opinion pages of the Minneapolis Star Tribune (first piece arguing that research for film was dubious, counter piece by producers about the research behind the film). The flare up nearly squelched the premier, although it ultimately took place.

Personally, I experienced how difficult it can be to establish a “consensus view” of how to describe nitrogen flows for the report on ecosystem indicators described in my previous post. There was a constant tension throughout the report process to “tell readers what to do with the information” rather than just “giving them the facts.” I believe we ultimately struck a good balance, however, we nearly had resignations of participants when we unintentionally pushed the line on the indicator dealing with the movement of nitrogen and got too close to pointing fingers. (more…)

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Anything New in the Story of Nitrogen Moving into the Gulf of Mexico?

by December 14, 2011

Dialogue Earth has roots in a broad, stakeholder-based national report on the condition and use of U.S. ecosystems published by the Heinz Center in Washington, D.C. (the report is available in hard-copy from Island Press). Curiosity about the ongoing relevance of these indicators has led me to dive in and see what, if anything, can be said about trends since the release of the report in 2008.

The first indicator in the spotlight is one that describes the movement of nitrogen (N) into major waterways, through run-off as well as point discharges such as sewage treatment facilities (here’s a link to download a pdf of the indicator). Why is this an important indicator of the state of U.S. ecosystems? Our explanation in the report does a good job of answering this question:

Nitrogen is an important plant nutrient and is essential to all life. Nitrogen is an abundant component of the earth’s atmosphere, but it is unavailable to most life in gaseous form. In order to be used by plants and other organisms, nitrogen gas must be “fixed,” or converted to a “reactive” form, that plants can use, such as nitrate. Nitrogen is fixed and accumulates in ecosystems through natural processes, such as the growth of nitrogen-fixing plants like clover and soybeans. However, human activity has greatly increased the amount of reactive nitrogen added to ecosystems. The largest human-caused input of nitrogen to ecosystems comes from the conversion of atmospheric nitrogen gas into fertilizers. Additional reactive nitrogen gas is produced by the combustion of fossil fuels. Reactive nitrogen from all these sources can ultimately enter streams and rivers. Excess nitrogen transported to coastal waters by rivers can lead to low oxygen conditions, threaten fish and animal life, and degrade coastal water quality. (more…)

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Bringing the Global Carbon Cycle to Quora

by December 3, 2011

In a recent post about building a knowledge base for general consumption on the topic of ocean acidification, I suggested that it would be wise to step back and address questions-and-answers about the carbon cycle. This is a cross-posting of a post I just put up on Quora: The Carbon Cycle, Starting in.

And, the first question is also up on Quora: What are the compartments in which carbon is stored on Earth? Do you have the credentials to answer this, or do you know someone who does? Please help out—I believe it will be a rewarding way to bridge the gap between the science community and the rest of society. Also, keep in mind that “upvoting,” adding comments for the author, or suggesting edits,  as soon as there is one or more answers will be a really great way to participate.

For anyone new to Quora, I’d encourage you to take a look at a new infographic and video that helps explain how to have a winning strategy within the Quora community.

Any and all feedback is welcome!

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How Do I Go About Answering A Question on Quora?

by December 3, 2011

As a follow-up to a first infographic designed to help newcomers make sense of Quora, a relatively new question-and-answer site on the Web, this new infographic targets those who are new and want to dive in and begin answering questions. It is posted as an answer to How do you answer a question on Quora? There already are some great resources on Quora for those who are getting started, such as Lucretia Pruitt’s post “Welcome to Quora. Do Yourself a Favor & Slow Down” (1663 upvotes, and counting) and What are the basic rules around using Quora?

As an experiment, I created a short (3 min) video that walks you through the infographic. Note that there are a bunch of links to Quora questions throughout the video—ensure annotations are turned on to see them. Feedback welcome!

And, the infographic…



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Making Decisions About Purchasing Alternative Vehicles

by November 28, 2011

In a recent post, I discussed Why Hybrid Cars Are Tough To Justify On Fuel Savings Alone and how Gallons per Mile (GPM) would be a better metric than Miles per Gallon (MPG) to use to compare vehicles. The gist of it is that we save a lot more fuel replacing a 15 MPG vehicle with one that gets 20 MPG compared to replacing a 30 MPG vehicle with one that gets 35 MPG. The GPM metric makes this intuitively obvious, whereas MPG does not.

A few weeks back when I dipped my cup into the Twitter river, which I need to do more often, I happened upon a press release from the U of Minnesota Extension having to do with a new spreadsheet tool designed by energy economist Doug Tiffany to help those considering an alternative vehicle purchase.

Tiffany’s tool allows the user to customize the data input, adjusting things like purchase price, down payments, expected cost of fuel, one’s personal opportunity cost (the cost to me for tying up cash for down payment and monthly car payments). The tool then produces several graphs, the first of which is a 15-year cumulative cost projection comparing several vehicle types. For the graph below, I used the default values in the tool, which can be downloaded here.


So, what this means, is that for the input parameters, the 15-year cumulative cost of ownership of the extended range vehicle, such as a Chevy Volt, comes out the highest, whereas the electric vehicle, like the Nissan Leaf, comes in with the lowest cost. The following graph shows the breakdown between car types at year 15.


Cost may not be the only motivator, however, at a time when many are concerned about greenhouse gas (GHG) emissions. Thus, it may be important for many to compare the estimated emissions of greenhouse gases from the different vehicle types. Tiffany’s tool produces this graph based on various inputs.


As would be expected, the conventional gasoline-powered vehicle has the highest emissions. There’s not as much difference between the other types, with the hybrid having somewhat higher GHG emissions than the all-electric, both of which do somewhat better than the extended range electric.

Tiffany’s tool reminded me of a widget available from my colleagues over at Climate Central, which is embedded below. It allows you to get a good sense of potential fuel and GHG emission savings between two different vehicles. It dynamically updates fuel costs for your state, which is a nice feature.

Together, these tools provide a great resource to anyone considering an alternative car purchase. Perhaps these groups could team up to create a tool that blends together both annual costs / savings and economics over the vehicle’s lifetime.

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The Role of Storage with Variable Energy Sources Like Wind and Solar

by November 8, 2011

In a recent post, I asked What’s Going To Happen To Your Vehicle’s Lithium Battery At the End Of Its Life? One of the options discussed in the NY Times article about the fate of batteries that sparked my post was as a means for storing electricity generated by wind turbines. A couple of other recent articles about energy storage caught my eye—both related to wind energy.

Why might storage play a key role in a grid that has a lot of wind turbines?

In early October, Mark Ahlstrom, the CEO of WindLogics, gave an excellent presentation as part of Frontiers in the Environment series at the U of MN’s Institute on the Environment (view the video here). He explained how our variable demand for electricity over the course of a typical day is met by a range of generation sources, from base load to “peakers.” Base load is met by nuclear, coal, and hyrdo—depending on location. Base load plants are meant to run 24/7, and adjustments to their output need to be scheduled well in advance. On the other end of the spectrum are peakers, which are small electrical generators that can be turned on with little notice and do not need to run for a minimum period of, say, a day. The figure below is based on a slide from Ahlstrom’s slides.


Ahlstrom went on to explain how things get interesting when a substantial amount of wind generators are added to the mix. In the figure below, the bright green line represents the reduced daily load that results by adding a number of wind turbines to this hypothetical typical energy demand. He goes on to explain how the rest of the electricity generators need to adapt to this new load curve, which can have more spikes and other challenges, such as a faster ramp-up in the early morning hours—challenges that the current energy system wasn’t set up to tackle.


Here’s a good piece by the ClimateWire group that landed in the NY Times: Fickle Winds, Intermittent Sunshine Start to Stress U.S. Power System. It dives into detail about the policy challenges that blending intermittent energy sources with our traditional electrical generation system.

Back to storage. A recent piece in the NY Times described how Batteries at a Wind Farm Help Control Output. In the largest battery installation connected to the grid in the U.S., they’ll use over a million batteries to provide storage for a few minutes of generated electricity from a large wind farm in West Virginia. The idea is that this stored electricity can be fed into the grid to help smooth things out when output from the wind turbines drops off momentarily. It is not designed to even out longer periods when the wind is calm. Significant storage on the time scale of hours and possibly days would most likely require a solution such as pumping water uphill or compressing air when the wind blows, and then using this stored energy to run a generator when the wind is quiet (here’s a project underway to study pumped hydro in conjunction with wind farms in northern Minnesota). There may also be options to store electricity in electric vehicles integrated with a smart grid of the future.

Finally, another NY Times piece that gave me some pause had to do using water heaters and electrical space heaters to store excess electricity brought about in part from excessive winds in the Pacific Northwest. The idea is that automated, shorter-term storage of excess electricity in homes that already have electric hot water heaters and heat with electricity could bleed off excess electricity pouring into the grid during storms when wind generators are running at maximum output (note that the situation was further complicated because hydropower operators were unable to reduce output from their generators for fear of creating conditions that might kill fish).

At a gut level, this strikes me as a good way to avert disaster, but probably not a great strategy from an energy efficiency standpoint. My sense is that using electricity for water heating and space heating is not nearly as efficient as, say, natural gas. The standard reason for arguing this point is that the efficiency of traditional energy plants is much less than 50%, whereas a high-efficiency hot water tank can exceed 90%. However, maybe this standard reasoning needs to be updated in a situation where electricity comes from wind or solar. This is a topic that merits further consideration.

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So You’re On Quora, Now What?

by October 16, 2011

As we gear up to tackle some basic questions and answers on Quora about the carbon cycle as part of our EarthQ project, with a goal of soon being able to tackle issues like ocean acidification and global warming, it seemed that a roadmap to Quora would be key for collaborators who might never have hear of it. Hence, the idea of a Quora Infographic emerged late this past week. Here’s version 0.1 that I’m throwing out for feedback. What do you think? Helpful? Silly? Gaping holes?


UPDATE: Now showing version 0.2, thanks to a comment from friend Mike Troiano to highlight the start arrow. Keep the comments coming!

Version 0.1

See this also on my post on Quora. I’d appreciate you up-voting it there if you like the idea.

Creative Commons License
So you’re on Quora, now what? by Dialogue Earth is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Permissions beyond the scope of this license should be submitted here.

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Building A Knowledge Base About Ocean Acidification on Quora

by October 13, 2011

Some months ago, we did a proof-of-concept video contest on the subject of ocean acidification. Here’s the winning video, about a snail that doesn’t have a shell, goes to learn why, and then forms a band to spread the word about this phenomenon.

Our overall vision is that we’d only initiate video, or other multimedia, projects once we’d nailed down the “science behind the story.” Furthermore, to us, nailing down the story means that we’ve ferreted out those key points for which we can get widespread agreement from experts drawn from across society–those from industry, NGOs, government, as well as academics.

To be blunt, we skipped this (huge) step for ocean acidification for two reasons. We were trying to proof out a crowd-based process for creating videos that conveyed science points fairly. Also, I had a good bit of background on the issue from my graduate work in oceanography.

102__0x0_quora-picture Now that we’re aiming to cultivate Q&As on Quora on topics related to the environment, it seems only logical to revisit the topic of ocean acidification. We’re dubbing this Quora-based project EarthQ (see also this post about putting candidates on the spot about global warming). For reference, see this post I did on the science behind the story of ocean acidification.

The goal of EarthQ will be to identify the top questions about various issues people are likely to ask about ocean acidification–assuming we can shepherd solid answers that are endorsed by a wide spectrum of experts. Taking this approach ties into Anticipating Questions People Will Ask About a Topic. Of course, if we’re successful, we will have created a great network of experts ready to jump to assistance as new questions emerge organically on Quora.

I’m a big advocate of working with building blocks on an issue. Having given this a good deal of thought recently, it is clear to me that step one will be to develop Q&A that fully explain the carbon cycle. Then, we can move on to the topic of ocean acidification. Then we should have worked out enough of the kinks to take on the topic of global warming. Onward!

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Capturing Mood About Daily Weather From Twitter Posts

by September 29, 2011

After considerable preparation, we’ve just launched a version of our interactive tool, Pulse. Using Pulse, users can explore feelings about the weather as expressed on Twitter.

We began the process by choosing a topic that would yield a substantial volume of discussion on Twitter as well as be of general interest. Once we settled on weather, we wrote a survey designed to gauge Twitter users’ sentiments about the topic. With the help of workers from the “crowd” accessed through CrowdFlower, we had tens of thousands of relevant tweets coded as to the expressed emotion about the weather. These results were then used to create an “instance” of the Pulse tool, which manifests as a map of the United States that at a glance reveals Twitter users’ sentiments about the weather in their region on a given day. (You can read more about the coding process here and our choice of weather as a topic here.)

For our launch of Pulse for weather, we chose to feature tweets published over a month beginning in late April, 2011, a period in which many extreme weather events occurred—the devastating tornado in Joplin, MO; widespread drought throughout the South; and flooding of the Mississippi River, among others. The image below is from May 25, three days following the Joplin tornado (jump to the interactive map here).


We gathered tweets from all 50 states as well as for about 50 metro areas. Here you can see a zoom up on several states centered on Missouri.


The interactive map tells part of the story, namely a state’s or city’s overall sentiment about the weather, while the content under the “Analysis” and “Events” tabs reveal some of the “why” behind this sentiment: what were some of the most notable weather events occurring on a given day? [Note: our "events" feature has a bug in it and is currently turned off. In the future, icons will show up on the map to highlight out-of-the-ordinary weather events, like outbreaks of tornadoes, persistent flooding or drought, etc.] To what extent did the weather deviate from normal conditions? Why were tweets from, say, the South, uniformly negative during a certain time? What was happening when we saw a single positive state amidst a region that was otherwise negative?

We hope that weather is just the beginning. We envision using the Pulse tool to visualize nationwide sentiments about more complex, nuanced topics in the future—a sample of emotions about gas prices is just around the corner, and see our preliminary work on opinions about global warming. For now, you can explore the Pulse tool here, and let us know what you think!

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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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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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