This site uses cookies. By continuing to use this site you agree to our use of cookies. To find out more, see our Privacy and Cookies policy.
Skip to the content

IOP A community website from IOP Publishing

Powered by Movable Type 4.34-en

Sustain to gain: May 2009 Archives

Cool cities

| | Comments (3) | TrackBacks (0)

Steven Chu is cheerleading another approach to fight global warming: Painting roofs and even pavements white to reflect sunlight. Such a measure is suggested to potentially offset 44 Gt of CO2 emissions via negative radiative forcing when implemented globally. White painting is related to a list of geo-engineering approaches, including ocean fertilization with iron and sending sulphate aerosols into the stratosphere. However, these approaches can endanger ecosystems, are potentially very limited in their efficacy, cost a lot and pose significant risks (e.g., see here for the sulphate case). It seems that white painting has less of these disadvantages, beside the need for more sunglasses.


White painting is also not an esoteric method. Precisely because is works so well, white painting is an established method all over the world. Consider the white towns in Andalusia and Nicaragua. From above, such a town - Arcos de la Frontera in Andalusia - looks like this.

Arcos de la Frontera in Andalusia. Source: Wikipedia.

Of course, the historic towns have not been built to mitigate or geo-engineer climate change. The motivation was simply to cool down the city in the summer heat. This observation is crucial to understand that climate change mitigation does not necessarily have to be conducted through the perspective of climate change. Cities may be motivated by the more direct impact of white painting, for example. The effect of white painting is double fold:

  • Direct: Higher urban albedo reduces summer temperature in cities
  • Indirect: Less air-conditioning is needed

Both effects mitigate climate change, benefit house dwellers, and benefit fellow city inhabitants. These co-benefits on different agent levels are pleasant from a game-theoretic perspective. Common national measures discussed in international negotiations are often framed in the context of a modified prisoner's dilemma where national action produces costs locally but externalizes the benefits. White painting, as well as many other measures, offers a no regret options for city dwellers. Either it helps to cool the global climate or it provides proper adaptation and protection for increased global heat. White painting has another advantage: no big investments or government action is needed. Motivated dwellers can act themselves, or municipalities can initiate urban schemes. Specifically, engaged US-cities do not need to wait for reluctant Congress. Action can be incremental and action is not dependent on a huge technological breakthrough.

Urban gardening or parks are another related measure to reduce the urban heat island effect and cool down cities. It would be interesting to explore to what degree urban greening and urban whitening complement or compete against each other and where what kind of strategy is more appropriate.>.

Colleagues from the Energy and Resources Group in Berkeley tell me that California and the Western States can be supplied to a significant part by concentrated solar power (CSP) in 2022 - at least upon the implementation of a carbon tax > $40/tCO2. CSP is also part of the suggested EU-supergrid. Is CSP the second renewable energy technology after wind that breaks through? Let us contrast the abstract macro-economic modeling with a business perspective. Here some insights that I gained from a financial analyst, Shujia Ma.

How does CSP compete with other energy sources?

A CSP plant can be compared with a gas plant where heat steam drives a turbine. The CSP plant itself is currently more expensive than the gas plant but no fuel costs have to be paid for - solar energy is free. In this regard, CSP is similar to photovoltaics (PV). In contrast to current PV installation, CSP relies on economies of scale and is supposed to be cheaper. However, due to its plant characteristics, additional transmission lines are needed that are not required for roof-top solar panels. CSP and wind operate in different market segments, as CSP operates more in peak demand times whereas wind is mostly available at night (in California).

What are the challenges that limit CSP deployment?

For the US, currently financing is the dominant challenge. The few banks that have sufficient resources are reluctant to lend money. Another problem is state regulation which is often very slow in processing applications. The market for CSP is relatively weird, as only two firms control important parts of the supply chain such as mirrors or tubes (part of the heat transfer system). More competition in the supply market would bring down costs significantly.

Can technological progress bring down the price of CSP closer to grid parity?

Yes. Advancement in materials will lower the price for CSP deployment. However, Solar Millenium is mostly a developer and does not have sufficient resources for extensive research. The CSP business relies on R&D from public research agencies such as NREL.

That leaves open the question what role policies play. The current renewable portfolio standards (RPS) of the western US states clearly pushes utilities to purchase large-scale renewable capacities, including CSP, and by thus developing the market. Important condition here is that the RPS is actually enforced. It is ironic that the US currently relies much more on this regulatory approach, and that is Europe that builds on market instruments. In fact, also in the US, a combination of carbon price and feed-in tariff, providing long-term reliable incentives for investors, could brighten up the market for CSP and other renewables. A US-Europe comparison is somehow narrow: Given low labor costs (important for CSP), good solar resources, fewer transmission line problems and the potential availability financial resources from the government and uncomplicated procedures, also China may turn out to become an important CSP player.

Obama has promised to put climate change front and center in Washington politics. As one of the first direct measures, Obama has directed the EPA to reconsider permitting California to impose tougher fuel standards. What does this measure mean for fighting climate change?

Obviously, measures in the transportation sector are very relevant to avoid potentially catastrophic climate change. In the US, transportation, and specifically motor vehicle use, is the largest and fastest growing source of GHG emissions among all energy sectors. Transportation alone accounts for one-third of all US emissions [1].

Current federal fuel standards (CAFE) are around 25 mpg. The Californian standards would require a fleet-wide average standard of around 35 mpg by 2016. An increase of 40% in this short time sounds quite ambitious. So is it even feasible? A look across the Atlantic is useful: by 2002, Europe already had an average consumption of 37 mpg. Just comparing these numbers, it is obvious that no technological barrier hinders California from reaching its goal. But where does this difference come from? Popular wisdom suggests that the Big Three--GM, Ford and Chrysler--were unable to develop advanced technologies. But this is not really the heart of the issue. In fact, the Detroit manufacturers contributed significant technological advancements over the last 20 years. What then is going on here?

It helps to understand what exactly "fuel efficiency" means. It turns out that fuel efficiency in the US, measured in miles per gallon, did not improve in the last two decades. Yet in that same period, manufacturers pushed heavier, more powerful cars onto the market. In fact, the consumption of gasoline per vehicle weight improved dramatically. In terms of consumption per vehicle weight, the US fleet is as good as any other region in the world [2]. Instead, the bad overall mileage is related to the high number of heavy tank-like vehicles on the streets. By 2008, more than half of all vehicle purchased in the US were SUVs or light trucks (the trend is currently changing though). So in effect, additional weight consumed all the technological improvement.

That makes one curious about why car purchases went up for heavier cars. SUVs became more popular worldwide, but especially so in the US. Is it simply that Americans like big cars more than the rest of the planet? It is probably true that gas-guzzlers are chosen as status symbols. But the story is richer. Many car owners, in fact, cite safety concerns: they can't ride a small car when others are riding big cars. It is an arms race. Where did it find its origin?

Let us go back to the fuel standards. As a leader, the US introduced fuel standards in the 1970s as a reaction to the oil crisis. The Big Three feared the incoming Japanese competition, which produced much more fuel-efficient and smaller cars. Doing what they do best, the Big Three lobbied Congress for loopholes for light trucks, exempting them from stringent regulation and taxes. At the same time, a 25% tax on imported pickup trucks was put into place. That didn't seem like a big deal then as those big cars made up a small market share. However, the Detroit manufacturers invested heavily in this loophole rather creating a new market for big and, due to their size, fuel-inefficient vehicles, than competing with the Japanese. [3] Detroit manufacturers chose an intermediate successful but ultimately dead-end strategy.

From this perspective, it looks much more like supply first created the demand for big vehicles. Dysfunctional fuel standards are partially to blame, allowing for different categories.

Comparison of fuel economy standards [4].

What lessons can the Obama administration learn from this when re-regulating fuel efficiency?

The Californian standard is promising but still adheres to the current double standard: a lower standard for SUVs and light trucks and a higher one for everybody else.. The updated federal CAFE standards from 2007 are also a step in the right direction, especially when the changes in the standards are front-loaded, i.e. the highest steps in fuel efficiency requirements must be taken first. The new CAFE standards are differentiated in size, i.e. larger cars have lower fuel efficiency requirements. This means that there is an incentive to reduce the vehicle weight for any given car size. However there is no incentives to reduce weight by going to smaller cars and promote them.

The Obama administration has indicated it wants to implement progressive but harmonized standards. (Harmonization makes sense, as it helps car manufacturers without harming greenhouse gas emissions). The harmonized standards could set weight independent standards. Another option is to supplement CAFE standards with market-based incentives for consumers to buy the overall more fuel-efficient cars, e.g. by a fee-bate scheme, where buyers of fuel-efficient cars get a rebate whereas buyers of fuel-inefficient cars pay a fee. This is a revenue neutral scheme.

There is much promise in fuel-efficiency standards. If Obama follows the proposed California regulation or a similar approach and implement them on federal level, overall US GHG emissions will be around 5-6% lower by 2016, assuming all else being constant. That is very successful achievement for a single measure!


[1] Energy Information Administration (EIA), Emissions of Greenhouse Gases in the United States 2004, Washington DC, 2005

[2] Lee Schipper, Automobile Fuel, Economy and CO2 Emissions in Industrialized Countries: Troubling Trends through 2005/6, EMBARQ, the World Resources Institute Center for Sustainable Transport, 2007

[3] Daniel Sperling, 2 billion cars, 2009.

[4] Feng An and Amanda Sauer, Comparison of Passenger Vehicle Fuel Economy and Greenhouse Gas Emission Standards around the World, Pew Center on Global Climate Change, 2004