Transitioning to a Low-Carbon Economy: Lifecycle Emissions

By Tyler Ellis

Much has written about the importance of transitioning to a low-carbon economy and what the new electricity mix should be according to the particular author’s preferences. However, not much has been written on actually how to transition to a low-carbon economy. To study this transition, a full “lifecycle analysis” should be performed to total up all of the emissions emitted from both the initial construction of the plant in addition to the necessary activities to support its operation. This is important because in order to construct new clean energy technologies, existing coal plants will have to be used. Thus, all new energy technologies will accumulate an “emissions debt” relative to coal that depends upon how energy intensive they are to manufacture and operate. It’s a useful exercise to look at the major alternative energy sources currently available to see both how long it takes to repay their “emissions debt” if ever, which could have implications on how fast this new generation should be built out, as well as what transition scenarios would allow for the least amount of emissions to the atmosphere.

The paper that I performed background calculations for, “Greenhouse gases, climate change and transition from coal to low-carbon electricity,” describes a full lifecycle model for all major electricity sources and drew two quite startling conclusions. First, unless society switches to energy sources that cut emissions by more than 90%, you don’t see much of a reduction in emissions levels. Proponents have argued that switching from coal to natural gas for power generation will cut emissions by 50%, however when you take into account the process of drilling for natural gas which leaks methane (a more powerful greenhouse gas than CO2), transportation of the fuel, construction of the new natural gas plant and other factors, climate-wise there’s almost no value in doing this.

Second, while a switch to renewable sources (like nuclear, wind, solar thermal, solar photovoltaic) does incur a carbon debt from initial construction, these sources do start to decrease emissions by the turn of the next century. Hydroelectric was purposefully not included in the list because according to the performed calculations, a new hydroelectric dam is actually worse than a coal plant for the first hundred years because of the rotting organic vegetation beneath the backed-up water which release appreciable amounts of methane. The figure below shows the predicted temperature increases over a 40 year transition from coal (represented by the solid black line) to the alternative energy source. The dashed line represents the predicted temperature increase if coal were replaced with an idealized zero emissions source.

IBEE Ellis LifeCycle

Although transitioning energy infrastructure is a very slow process and emissions have a long legacy due to the length of time they stay up in the atmosphere, one of the major takeaways from this write-up is the urgency that the US should have in developing transition plans to low-carbon energy generation technologies. The more we delay this transition, the greater the environmental harm that will be caused.


About macomberjohnd

HBS Finance faculty interested in sustainability in the built environment including devices, structures, townships, and cities.

3 Responses to “Transitioning to a Low-Carbon Economy: Lifecycle Emissions”

  1. The issue of methane release from behind dams is very real and seldom counted. Here is a piece in The Economist about the Belo Monte dam:

    “In the 20th century thousands of dams were built around the world. Some were disasters: Brazil’s Balbina dam near Manaus, put up in the 1980s, flooded 2,400 square km (930 square miles) of rainforest for a piffling capacity of 250MW. Its vast, stagnant reservoir makes it a “methane factory”, says Philip Fearnside of the National Institute for Amazonian Research, a government body in Manaus. Proportionate to output, it emits far more greenhouse gases than even the most inefficient coal plant.”

    Life cycle costing, or maybe “fully loaded costing,” of renewables projects has to be considered. Anecdotally, I’ve also been to “net zero” buildings made of cast in place concrete. Even if they are net zero from an operating point of view, they will never make up for the embodied energy to manufacture the cement in the concrete.

  2. I enjoyed this post and thought the use of full lifecycle modeling to assess emissions reduction for renewable energy sources was an interesting framework. I wonder if there are ways for policymakers, corporations, or other organizations to use full lifecycle modeling to improve environmental impact. For example, could full lifecycle modeling be part of the certification processes for new projects (such as LEED certifications)? For governments, could full lifecycle modeling be a component of their decisions for permitting and subsidization? It seems that agreeing to a universally acceptable method for assessing lifecycle emissions remains in development, but if parties could agree on a standardized approach, I would welcome means for using this as a framework in corporate and government decision-making.

  3. Thanks for the interesting post. I had never considered the adverse GHG impacts of rotting vegetation from creating hydro dams. This got me thinking about other situations where a lifecycle analysis needs to be highlighted.

    A noteworthy example (related to the LEED reference in the above reply) is with building materials. A few years ago I came across buildings constructed with walls of “structural insulated panels” (SIPs) []. SIPs are typically constructed of sheets of OSB (similar to plywood) with 6+ inches of expanded polystyrene or polyurethane (think Styrofoam). SIP walls are more resistant to heat transfer (R value of 21.6) compared to 2×4 wood-framed wall with fiberglass insulation (R=9.8). Thus SIP wall homes can be constructed in cold-climates and require much less energy to heat (or cool in hot-climates). The winter heating costs for a SIP home constructed in Minnesota could easily be half that of a wood-frame (average home ~$500/winter). SIP construction is more expensive than standard wood frame, and additional, detailed analysis should be performed to weight higher upfront costs and recurring energy savings under different scenarios.

    However, the final disposition of these foam walls must be considered since this foam can take thousands of years to decompose. A 2-story home with 2000 square feet and 6” SIP walls would contain about 1500 cubic feet of foam. This is equal to about 700,000 foam coffee cups, which cancels out the benefits of using a reusable mug!

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