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Hybrids Better for Climate than Leaf, Tesla in Most States

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A Roadmap to Climate-Friendly Cars

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Press Release: 

An electric car is only as good for the climate as the electricity used to power it. And in states that rely heavily on fossil fuels like coal and natural gas for their electricity there are many conventional and plug-in hybrid electric vehicles that are better for the climate than all-electric cars today.

But that is just part of the story. Another critical factor is the carbon emissions generated when a car is manufactured. Emissions from producing the battery and other electrical components create a 10,000 to 40,000-pound carbon debt for electric cars that can only be overcome after tens, or even hundreds of thousands of miles of driving and recharging from clean energy sources.

MORE: You Asked, We Answered: Response to 2013 Cars Report

This comprehensive state-by-state analysis of the climate impacts of the electric car, plug-in hybrid electrics, and high-mileage, gas-powered hybrid cars takes both of these factors into account – the source of energy used to power the car and carbon emissions from vehicle manufacturing.

We found:

  • In 40 states, a high-efficiency, conventional gas-powered hybrid, like the Toyota Prius, is better for the climate (produces fewer total “lifecycle” carbon emissions) than the least-polluting, all-electric vehicle, the Honda Fit, over the first 50,000 miles the car is driven.
  • In 26 states, an efficient plug-in hybrid is the most climate-friendly option (narrowly outperforming all-electrics in 10 states, assuming a 50:50 split between driving on gas and electric for the plug-in hybrid), and in the other 24 states, a gas-powered car is the best. All-electrics and plug-in hybrids are best in states with green electrical grids with substantial amounts of hydro, nuclear and wind power that produce essentially no carbon emissions. Conventional hybrids are best in states where electricity comes primarily from coal and natural gas.
  • For luxury sedans, in 46 states, the gas-powered Lexus ES hybrid is better for the climate than the electric Tesla Model S, over the first 100,000 miles the car is driven.

Greener Grid Needed to Reap Benefits of Electric Cars

In just two years, from 2010 to 2012, a greener grid from more natural gas and wind-generated electricity led to an 8 percent reduction in carbon emissions per kilowatt-hour generated nationally. Combined with more efficient electric cars:

  • This reduction in carbon emissions from electric power generation more than doubled the number of states where driving and charging a high-efficiency all-electric vehicle (but not counting any vehicle manufacturing emissions) is better for the climate than a gasoline-powered Toyota Prius hybrid; from 13 in 2010, to 32 states in 2012. (The Prius is the most climate friendly conventional hybrid/gasoline powered vehicle on the market.)

But when all the carbon emissions associated with building and driving electric and high-mileage gasoline cars are included in the analysis, the all-electric advantage goes up in smoke. In the vast majority of states, the significant carbon debt associated with the production of electric car batteries outweighs recent reductions in carbon emissions from power generation and efficiency improvements of some electric vehicles.

State By State Summary

Swing states. In many states the rapid substitution of coal with natural gas and the adoption of substantial amounts of wind power have measurably decarbonized the grid from 2010 to 2012.These changes have shifted the balance of carbon emissions in favor of recharging electrics vs. burning gasoline in high-mileage hybrids like the Prius, if car manufacturing emissions are excluded.

Click image to enlarge.

In Pennsylvania, Virginia, and Alabama, the share of electricity generated with natural gas increased by about 10 percentage points while coal’s share dropped an equivalent amount. In Texas, natural gas generated electricity is up about 5 percentage points, with coal down the same, and wind now accounts for 9 percent of the state’s power. In Iowa, coal use dropped 10 percentage points and wind power jumped 8 percentage points, while in Nevada coal fell 10 percentage points, natural gas was up 5 percentage points and solar was up 3 percentage points.

In all these states, a relatively modest shift to less carbon intensive electricity generation — generally around a 10 percent shift from coal to gas or an equivalent increase in the percentage of wind or solar — pushed all-electric vehicles ahead of conventional hybrids in terms of climate benefits associated with driving and recharging (but not including manufacturing emissions).

But when manufacturing emissions are included, gas-powered hybrids, or plug-in hybrids, which run on mix of gas and electricity, are the most climate-friendly choice.

Dirty Energy States. Eighteen states, including Colorado, Missouri, New Mexico, Michigan, and Ohio, still heavily depend on coal, or have virtually no renewables and little nuclear power in their electricity mixes. Driving and recharging an electric car in these states is worse for the climate than burning gasoline in a conventional hybrid or high-mileage car. Including manufacturing emissions in the calculations makes the electric car even less climate friendly.

Climate-Friendly Electricity States. In 10 states (Washington, Oregon, Connecticut, Idaho,Vermont, New York, New Jersey, New Hampshire, South Carolina, and South Dakota), the best electrics are better for the climate than any gasoline car even when manufacturing emissions are included. Washington, Oregon, Idaho and Vermont have the cleanest grids, producing few carbon emissions, primarily through reliance on hydropower, nuclear, and small percentages of wind and solar. In these states, the mpg equivalents of the best electric vehicle are dazzling, ranging from more than 2,600 mpg in Vermont, to 380 mpg in Washington, 280 mpg in Idaho, and 200 mpg in Oregon.

Full List of Cars at 50,000 miles

Full List of Cars at 100,000 miles

Related Content
Roadmap to Climate-Friendly Cars: 2012
Fossil Fuels to Dominate World Energy Use Through 2040
Limiting Methane Leaks Critical to Gas, Climate Benefits 
EIA’s Most Important Insights About Our Energy Future


By Andrew (92627)
on August 8th, 2013

There is one massive flaw in this study.  The study does not account for the production pollution including extraction, transportation, refnining and further transportation to get gasoline to your car.  If the study includes the carbon emissions of building the battery you should count the carbon emmissions of creating gasoline.  Apples to oranges right now, which is not appropriate for a “scientific” study.

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By Paul (Madison/WI/53562)
on January 16th, 2014

Unfortunately as Andrew points out, this study is misleading.  When corrected it will provide excellent information for choosing a car.

Climate Central - when will the study be updated?

Thank you for your commitment to increase public awareness of climate change and for promoting ways to reduce greenhouse gases.

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By Paul (Madison/WI/53562)
on January 16th, 2014

can disregard my recent comment….  I just saw further down that this was addressed.


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By Foo
on August 8th, 2013

I’ve gone through the report several times, and it appears that the authors have made a serious methodological blunder with regard to plug-in hybrids. 

Consider the ranking of the Chevy Volt. This car is ranked lower, in terms of driving emissions, than the #1 Prius Plug-In, various other hybrids, and plug-in hybrids, and various battery cars.  The question is: why would the Prius Plug-In be #1, higher than a Prius, and the Volt be fairly low?

There’s only one real possibility.  The Volt has a relatively less efficient gas engine than the Prius Plug-In, and obviously a larger battery.  So if the Volt were driven long distances which obviated the value of its plug-in battery charging, it’d clearly be lower than these cars.  The problem is that this does not reflect actual driving patterns of Volt drivers.  These patterns are very well established from automated driving logs available online: Volt drivers drive the large majority of their time solely on battery.  This makes the car essentially an electric vehicle, but with half the battery weight of (say) the Leaf.

Then there’s the problem of the Prius Plug-In outperforming the regular Prius.  If driving long distances mitigates the value of the plug-in battery (and indeed the Plug-In’s battery is tiny, good for only about 8 miles) how is it outperforming a regular Prius, and yet larger battery cars are not?  So does battery equal worse climate (that is, Prius Plug-In > Volt) or does more battery equal better climate (that is, Prius Plug-In > Prius)?  This is just one example of some very fishy and counterintuitive rankings without much methodological explanation.

I think the problem here is that the authors do not state the driving patterns used in their model.  They only state vague total-number-of-miles values, not information such as miles driven between daily recharges,  And I suspect the reason for that is that their model is either brutally simplistic or completely incorrect when it comes to driver habits in these cars.  It’s the only explanation I can think of to justify the crazy ordering they came up with when ranking the plug-in vehicles.  The thing is, driving characteristics are *everything* when it comes to plug-in vehicles.  If driven long distances daily, a Volt will clearly underperform a hybrid, much less a Prius Plug-In.  But with short distances, the Volt would be expected to smack them every which way.

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By Sonyo Crown (Vertile/SP/8538)
on August 9th, 2013

Tesla corp can increase sale in elenven states in the US but the current Wanent Wanese head thought is To decrease all the bad PR Utah Is getting abouts it natural gas out-put Tesla can launch ad campaigns with the information in this article…LOL

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By Lewis Cleverdon
on August 9th, 2013

Why is it that this report, like dozens of others on EVs and hundreds on the renewable power technologies, cannot acknowledge a common glaring flaw in their analyses ? As a rule they studiously ignore the fact that every scrap of fossil fuel displaced by the tech in question is then bought and burnt elsewhere. These technologies do Not reduce fossil fuel consumption, and it is highly misleading to imply that they do. They simply transfer the fossil fuel’s combustion elsewhere. That’s the reality, and as a science-based site it should surely be acknowledged here.

Politically, the steady hype over non-fossil techs serves a very clear agenda: that of undermining public demand for a commensurate binding global climate treaty - While it is rarely stated brazenly there is the strong implication within the hype that with renewables growing ‘so fast’ the global climate treaty is, as Obama’s mouthpiece lied to the UN “both unnecessary and un-doable.”

It is only that treaty that can define all nations’ tradable CO2e-emission permits, declining annually under a contracting global carbon budget while converging towards international per capita parity of permits by an agreed date. Only that halt on nations’ ability to buy in the fossil fuels displaced by renewables gives the latter any useful function. Without that treaty they are merely wishful thinking, an income stream to developers, and a pernicious diversion of public attention from the key issue of the treaty’s negotiation.

So where is the public discussion of what form and stringency the treaty should take to provide the necessary and sufficient changes to avoid looming global crop failures, consequent geopolitical destabilization, and resulting terminal decline ? Sites focussed on climate are almost universally silent on this issue - apart from annual accounts of the trivia of the latest COP outcomes.  Perhaps a programmed flag-nationalism is one part of the reticence - the belief that “Our diplomats are the ones in the white hats” but the paternalist delusion that “Foreign policy is too difficult for ordinary people” also play its part.

I don’t suggest that the authors and publishers of articles such as the above are aware of these dynamics - but I do suggest that it is long past time they woke up to the way their efforts are being used to help maintain the reckless bipartisan US policy of a Brinkmanship of Inaction with China. That policy cannot survive being exposed to the public’s attention, but how many sites will find the commitment to acknowledge, publicize and criticize it and propose the requisite alternative, that the US starts negotiating constructively ?

Most will doubtless continue with the BAU of discussing the science, revelling in the tribalism of the diversionary circus of denial, and hyping the renewables as the great white hope - but how about Climate Central ?



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By Chris Suich (Apex/NC/27502)
on August 9th, 2013

This report
has so many contradictory statements; very difficult to read.
The figures and tables lead you to believe Prius is better, the body of the report favors the Leaf.

Example 1:
Table 1:
”State-by-state emissions of the Nissan Leaf. The Prius emits 0.52lbs CO2e/mile. Compared to the Leaf, the Prius is the more climate-friendly option in 32 states when driving emissions are compared.”

Yet the body of the report
“Driving a Nissan Leaf produces fewer greenhouse
gas emissions than driving a Toyota Prius in 32 states
(Figure 1). In 18 states, making electricity generates
so much climate pollution that charging and driving a
“zero-emissions” Nissan Leaf in those states is worse
for the climate than driving a gasoline-powered Prius.”

Example 2:

Figure 2:
“In 10 States Gas Powered Cars Need Fuel Economies Of At Least 80 Miles Per Gallon to Produce Fewer Emissions Than the Electric Leaf (Excluding Manufacturing Emissions)”

Table 2:
“A gas-powered car needs to get at least 34 miles per gallon to be more climate friendly than a Leaf in all states”

Yet in the body of the report
“Where the electrical grid is the least carbon
intensive, including Washington, Idaho, and Oregon,a
gas-powered vehicle would need fuel efficiencies of at
least 200 miles per gallon to beat the Leaf. In Vermont,
a conventional car would need to get over 2,600 miles
per gallon to be more climate-friendly than the Leaf”

In states like Kentucky, Indiana, and Wyoming, for example,
gaspowered cars only need to have fuel efficiencies of
34-37 miles per gallon to be the most climate-friendly
options for drivers”

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By Foo
on August 9th, 2013

Lewis, it would appear you didn’t read the study at all.  The authors take great pains to consider the fact that electric vehicles, in many states, simply burn fossil fuels elsewhere, such as coal or natural gas through power plants.  That was the WHOLE POINT OF THE STUDY.  Your entire screed is based on not only a falsehood, but a bizarrely ignorant one.

In response to your comment though: a bunch of states are primarily powered by nuclear or hydroelectric plants.  The study authors painstakingly consider, state by state, which states are better for electric vehicles, CO2-wise, and which are worse, and by how much.  You seem to dismiss this fact entirely.

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By scratch (LA CA)
on August 9th, 2013

Another study that uses “magic fuel” to power gasoline and gas-hybrid cars. The energy used to refine gasoline is massive. In California the 2nd largest user of electricity in the state are the oil refineries. You could drive a Nissan Leaf 22 miles just on the energy it takes to refine one gallon of gasoline.

Calculating in that massive energy use and the energy spent in the global searching for oil, the extraction, transportation, pumping to storage facilities, pumping to tankers for oceanic shipping (tankers get about 60 FEET per gallon on the dirtiest fuel available), more pumping onshore to the coastal refineries (see above stats)  and then pumping and transporting to gasoline stations and pumping into gas tanks for burning up. All this happens continuously for the entire 50,000 or 100,000 mile life of the gasoline or hybrid car. For an electric vehicle you make a battery once. And then magically you can recycle it.

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By Kevin (Southern California)
on August 9th, 2013

Do the electric grid assumptions in California account for the permanent closure of San Onofre Nuclear Generating plant?

This provided 25% of the electric energy in SoCal essentially carbon-free.  But no longer…  This would seem to skew the numbers poorly for California, right in the heart of Tesla territory. Half the neighbors on my street have electric or plug-in hybrids.

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By Daniel (Climate Central)
on August 9th, 2013

@Andrew: We calculated emissions associated with producing and transporting gasoline using the “Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation” (GREET) model developed at the Argonne National Laboratory. This part of our methodology is described in full on page 24 of the report.

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By Brandon Kuczenski (Santa Barbara CA 93110)
on August 9th, 2013

First: the study does take into account the fuel cycle emissions, so Andrew (92627)‘s and Scratch (LA CA)‘s comments are just wrong. Report page 23: “A gallon of gasoline releases about
19 lbs of CO2 when burned. To these CO2 emissions we must add the GHG emissions associated with extracting, transporting, and refining the crude oil used to make that gallon of gasoline. When these are included, the total GHG emissions for using gasoline in a car come to 25.9 lbs of CO2-equivalent per gallon.” Their source for those figures is the Argonne GREET model, which (despite its flaws) is uncontested as the credible source for this information in the US.

Other comments, such as Foo’s rambling one, can be grouped under the heading of “uncertainty”.  It seems the biggest flaw of the study is that it fails to quantify its uncertainty- certainly a common problem in LCA. The report includes bombastic and unsupported statements like “goes up in smoke” that suggest the authors are not impartial. They don’t take into account driving patterns (but really, the driving pattern used should be the same for all vehicles). A proper analysis should look at consumption mixes, not production mixes (see Marriott + Matthews 2005 - ES&T 39(22)) DOI: 10.1021/es0506859. Those are pretty much the same for all states in a given interconnect, because they are all trading off the same grid. A bigger problem is accounting for the time of day when charging occurs- if the cars are charged at peak hours then dirty peaker plants will be providing the power; versus charged at night when a larger fraction of every grid is nuclear. (see, e.g., McCarthy and Yang 2010, J power sources 195(7) DOI: 10.1016/j.jpowsour.2009.10.024)

Overall, like in any LCA, many simplifying assumptions are made and no effort is made to quantify the effects of those assumptions on the results.

That said, it is a reputable study and though you may disagree with the results, the only meaningful criticism is to cite another study that found different results. The results presented here are not unreasonable, though not “true” either.  They are model outcomes; different models will predict different outcomes, and the truth is somewhere in the middle.

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By Karl
on August 9th, 2013

And for our next shocking revelation: driving your old, gas-powered sedan a year longer is more climate friendly than buying a new hybrid, plug-in hybrid or electric.  Film at 11.

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By Lewis Cleverdon
on August 9th, 2013

Foo - you fail to understand the core of what you call my screed:
- that any and every saving of fossil fuel by the use of EVs are, like those of the expanding non-fossil energy supply technologies,
promptly negated by that same volume of fossil fuel being bought and burnt elsewhere.

That is the reality of the present position: these technologies are doing nothing to reduce global anthro-CO2 output at all.
They merely add some energy supply globally over and above that from the total fossil energy output.

From the perspective of controlling anthropogenic global warming, both EVs and Renewables are not simply irrelevant as a means of controlling the total CO2 output,
misplaced faith in them actively obscures the need for the crucial global climate treaty to achieve that control
by boosting a delusion of mitigation by these technologies’ deployment by market forces.

The article’s authors entirely overlook the context of the technology they’re writing about, and repeatedly make erroneous claims of its relative benefits in different US states with regard to the global climate.
Whether you want to hold on to those delusions is up to you, but if you want to help get the mitigation of AGW under way then you’d do well to start dumping them.



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By Daniel (Climate Central)
on August 9th, 2013

@ Foo : In reference to your first comment, you are completely right. The relative impact of a plug-in hybrid does vary greatly depending on how far the car is driven on electricity, versus how far it is driven on gasoline. Driving more on electricity shrinks the car’s footprint in clean energy states, but can increase the car’s footprint in coal-reliant states. In this paper, we assumed a 50:50 split (see footnote 3). But that ratio can change if the car is only used for short-distance trips, and is recharged each time, for example.

For a full breakdown of these changes, see pages 5, 7 and 21 of the report we published last year:


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By Phil Blackwood (Lincroft, NJ 07738)
on August 9th, 2013

Many of us who buy electric cars to reduce are carbon footprint are aware enough to take the extra step to get clean electricity. 

Here’s where you can find the clean options:

And many of install solar panels as well.

The report should at least mention these options for coming out ahead in the “dirty” states.

I find this to be a serious omission that leaves the article misleading.

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By Will Toor (Boulder, CO, 80304)
on August 9th, 2013

This is an interesting report, but I would be very careful about the conclusions you draw. My colleagues and I at the Southwest Energy Efficiency Project have recently published two reports analyzing emissions from EVs in 6 southwestern states in 2013 and also in 2020 (available at and Fuel EmissionsFNL.pdf). We come to similar numbers for 2013, but in a number of states (especially Colorado) the trajectory is towards a much cleaner electricity mix during the lifetime of vehicles purchased today - in CO lifecycle GHG drops from over 400 gm CO2e/mile to 250 by 2020, and this trajectory likely continues past 2020. And, from a policy perspective, polices adopted today to support increased market penetration of EVs will likely have much of their effect on the market in future years, so future year generation mix may be more relevant than today’s mix.- Dr. Will Toor, transportation policy director, Southwest Energy Efficiency Project

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By Paul Scott
on August 9th, 2013

In response to Lewis Cleverdon’s comment, “As a rule they studiously ignore the fact that every scrap of fossil fuel displaced by the tech in question is then bought and burnt elsewhere. These technologies do Not reduce fossil fuel consumption, and it is highly misleading to imply that they do.”

On the contrary, the use of electricity does indeed reduce fossil fuel consumption. Cleverdon is correct in that at current production levels, 100% of the oil is going to be used somewhere, however, in the past year and a half, over 120,000 Americans have purchased or leased plug in cars, so they are no longer using oil as the energy source for their driving. Had they not done so, there would be even more demand for oil than there is now. This is the flaw in Cleverdon’s thinking.

The adoption rate for EVs is significantly higher than the original hybrids of a decade ago. Tesla, Nissan and GM currently dominate sales, but other OEMs are getting into the game and we’re seeing a rapidly accelerating adoption of these cars. Given the huge number of ICE vehicles being made and sold in China and India, we’ll continue to see 100% of the oil production used for many years to come, but there will be a time, maybe within 5 - 8 years when the growth of the EV sector will begin slowing the growth of ICE, and within 2-3 decades we’ll see ICE begin to fade from our car showrooms.

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By John Flanery (Eugene/OR/97402)
on August 10th, 2013

Further flaws: the report characterizes the marginal additional electricity as identical to the average electricity mix.  Yes, here in the northwest we have a lot of hydro, but we’ve pretty much exploited that resource; additional capacity is likely to be natural gas.  Unless of course the car is charged off-peak, which brings up another flaw:
If coal generates the electricity, but the car is charged off-peak, the car really isn’t causing additional fuels to be burned - the coal is going to get burned anyway.

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By paul (Boulder, CO 80302)
on August 10th, 2013

I did not read the entire report, but few will and what upsets me is the way the media presents these studies to the public.  The public just reads the headlines and assumes it’s true.  If “well to wheel” is calculated how can a gas car be cleaner than an electric vehicle?

Other reports state that each gallon of gas takes approx 6kwh of electricity to refine, indirectly adding even more emissions to gas cars in “coal states” (assuming their gas is refined in-state).

Why not just use the electricity to push the car around? 
As Scratch commented above, 6kwh of electricity will propel a Nissan Leaf 22-24 miles….or just refine 1 gallon of gas to get burned in a regular car.

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By eric (Colorado)
on August 10th, 2013

I’m surprised to find that Colorado is in a “dirty” energy zone.  Nearly 20% of power from xcel comes from wind, and I think we have a not-insubstantial amount of solar. Thus, an electric would run about 25% on renewables.

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By Mark D Larsen (Ivins, Utah 84738)
on August 10th, 2013

I deem this article an oily wolf in sheep’s clothing. For whatever it’s worth, those interested can read my critique here:

Petrolganda on Greenhouse Gases

Mark D Larsen

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By Hans
on August 11th, 2013

You can offset 40000 lbs of carbon emissions for $238 at TerraPass. Then your EV does not have any “carbon debt” due to manufacturing the battery.

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By Robert (Apsley, Ontario Canada)
on August 12th, 2013

Solar and wind power will not be reliable enough to face the new giant super storms of the future. There is no such thing as a “green” car. Cars drive on roads made of tar which come from oil refinery waste. James Hansen wants us to burn nuclear waste. We cannot store nuclear waste in super expensive caskets for 10,000 years safely when we can’t even guarantee our own survival for the next 100 years.
Here is the situation.
When ice ages come and go the planet can change temperature 4-7°C in as little as 5,000 years. 50 times slower than what we are doing. In the past, a 5°C change normally would take 20,000 years, we are going to do 5°C in 50-100 years, 200 times faster.
Climate change is happening 100 times faster than in the past.
The acidity of the oceans will more than double in the next 40 years. This rate is 10 times faster than during earth’s biggest mass extinction event of 250 million years ago when 95 percent of life on earth vanished.
Climate is changing 10,000 times faster than evolution can adapt.
There were thousands of 1-kilometer wide bubbling methane seabeds recorded in September, 2011.
Only 1% of methane needs to be released to cause total disaster.
Natalia Shakhova interview
Peter Wadhams interview

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By James (Boulder, CO)
on August 12th, 2013

This study does not seem to take into consideration the time of day when electric vehicles are charged. If the EV owners have incentive to charge their vehicle during off-peak hours, this has a tremendous impact on the resulting emissions. Especially in states where coal is the bulk of power, charging vehicles at night will likely not result in higher emissions.

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By Lewis Cleverdon
on August 12th, 2013

Paul, thanks for your response.
While it seems we’re agreed that any and every bit of fossil fuel displaced by EV’s and renewables is then bought and burnt elsewhere, meaning that these technologies do nothing at all to reduce global CO2 emissions, you suggest that they are reducing the growth of those emissions:
“Cleverdon is correct in that at current production levels, 100% of the oil is going to be used somewhere, however, in the past year and a half, over 120,000 Americans have purchased or leased plug in cars, so they are no longer using oil as the energy source for their driving. Had they not done so, there would be even more demand for oil than there is now. “

This assertion overlooks two practical realities.
First, even with oil at around $100/barrel, there has been only a marginal increase in global production over the last eight years - having burnt the easy resources the rising difficulty of oil’s extraction means that additional demand does not simply generate additional supply.
Second, if EV buyers were still running their ICE vehicles, as members of the planet’s wealthiest nation their demand would have outbid others for that supply, with some people at the poor end of the market finding the fuel unaffordable and having to go without it. This is the normal working of a market economy.

If at some point Renewable energy supply were to expand at a rate much faster than the rise of global energy demand, causing fossil fuel prices to fall marginally, the rate of growth of new high-cost fossil extraction projects could be affected, but this is scarcely providing any significant cut in global CO2 output. Only a commensurate global climate treaty can achieve that by setting formal annually contracting limits on all nations’ CO2 outputs. At that point, the “bought & burnt elsewhere” issue is resolved, and the renewables are able to actually replace fossil fuels and end our global dependence on them.

At present, the EVs and renewables are being hyped as a solution in their own right (as a matter of White House promotion) which is patently untrue, and which is directly damaging in undermining demand for the pivotally important UN treaty (which the White House undermines at the UN by claiming it is “unneccessary and un-doable”). I’m sorry to see the scientists of Climate Central being caught up in that hype without making crystal clear the central limitation of EVs’ efficacy for CO2 control.



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By Shawn Otto (Marine on St Croix, MN 55047)
on August 13th, 2013

Coal fired plants dump their excess power into heat sinks at night, so charging an EV off peak in a coal fired service area, as most EVs are charged at least in part now (off peak), uses electricity that is otherwise being generated and wasted, and so does not add carbon emissions. This is in effect the same thing as improving energy efficiency through better insulation and should be calculated as a net reduction. Perhaps I missed it, but I didn’t see this addressed.

I also concur with Will Toor’s caution re life cycle reductions, which tend to accelerate, but which are difficult to quantify with precision. That does not make them any less critical to include in this sort of analysis, since a car is not a single year investment but is driven over a lifespan of ten to twenty years.

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By Lynn (Edinburg, TX)
on August 13th, 2013

Well, of course, one needs to also get into alt energy if feasible.  We were on 100% wind from Green Mountain for years before buying our Chevy Volt, and are (as I write) installing solar panels—which is an investment we can’t refuse, with 30% gov tax break and $7500 incentive from AEP (who is our base electricity provider).  Texans, get onto this if you have a south sloping roof and are paying income tax above $5000.

Up north in near Chicago our electricity was 75% nuke, 25% coal.  A ComEd guy come to our env group and we discussed how to reduce that coal portion…..which they need as peaking power during high demand, bec nuke has to run constant.  We talked about pumping up water into a reservoir at night, then turning it to hydro-power during high demand times.

When I brought up EVs, the ComEd guy got excited & said, if enough people had EVs and were charging them at night they could cut their electricity rate in half smile  So, IL ComEd users, it is your civic duty to get an EV.

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By Carl Hage (Sunnyvale, CA)
on August 13th, 2013

It’s good to see a more detailed analysis of indirect CO2 emissions from EVs instead of using the simplistic US Average. Though touts peer-reviewed scientists, it appears this report was not peer reviewed.

One major problem is reliance on a single source (the Hawkins paper) for estimates of EV manufacturing emissions, in turn based on another single source from the same institution. The numbers in Hawkins and extrapolated by this ClimateCentral report do not seem credible, and there was little discussion of alternative estimates of EV manufacturing. Even the Hawkins paper mentions their estimate of 22 kg-CO2/kg-battery is more than other estimates of 6 and 9.6. The Hawkins paper assumes a motor twice as heavy as an actual Leaf motor in estimating copper and aluminum smelting CO2. Likewise, other parts of the EV power train and charging seem to have unrealistic assumptions for CO2. With some difficulty, I followed the chain of references in composing the estimates for EV manufacturing CO2 and found them to be unrealistic. The errors are compounded by making assumptions based on scaled curb weight.

A better source of CO2 from battery manufacturing is <> Plugging in some actual numbers for the LiMn2O4 Leaf battery (it is not LiFePO4), the 1521 kg-CO2/leaf-battery in the EPA report (with better sourced data from manufacturers) doesn’t match the ClimateCentral calculated 5224kg. EV CO2 emissions in the ClimateCentral report appear to be about 3-4 times higher than more credible sources for an emissions model.

The ClimateCentral report assumes the life of an EV to be 50K miles and sometimes 100K, rather than a more realistic 150/200K. Choosing 50K miles has an appearance of a bias in the author to prove EVs as bad for the environment. So the per-mile CO2 of battery should be another factor of 3 less, meaning the EV CO2 emissions from the battery are likely to be an order of magnitude off.

Even with the apparently pessimistic assumptions on car lifetimes and CO2 of battery manufacture, a look at the uncertainty in the model (which wasn’t done) would show that the error in estimates of CO2 is much larger than the differences in (short) lifetime emissions between a Prius and Leaf in states with emissions near the US average. So the moral should be that even including pessimistic assumptions on manufacturing-related CO2, the amount of CO2 emission is comparable to petroleum-hybrids for most states currently with substantial coal-based electricity, and states with cleaner energy have even lower CO2 emissions. Besides CO2, there are other good reasons to substitute home-made electricity for imported oil.

Also mentioned above is the ClimateCentral report’s analysis of the change in CO2/kWh across the US between 2010 and 2012 and future implications. The lifetime comparison of EV vs hybrid assume states will stay at the 2012 emissions level rather than improve. So if I go to the dealer today and want to compare lifetime CO2 of a Leaf and Prius, I need to make some assumptions on the future CO2 intensity of electricity. Using a more realistic 10year 150K car lifetime, I should use CO2 electric estimates around 2018 not 2012. If CO2 reductions continue as noted between 2010-2012, the results shown in the ClimateCentral report will be quite different (more favorable to EVs).

There is also an issue of assessing past sins in subsidized coal generation to new uses of electricity. If we compare new uses for electricity and new generation, the incremental change makes EVs more favorable. Wind energy is currently the least-cost new generation technology, and the most common new form of generation last year (see other GTM articles). EV buyers often support renewable energy, e.g. by installing solar panels with comparable generation capacity as their EV. So the CO2 from marginal electricity is different than the per-capita statewide average.

Sadly, anti-environmentalists will quote this report as proof that EVs are bad for the environment, not bothering to even read it. The real message is that as we move to a cleaner electric generation grid, the benefits of EVs become even greater and apply to states with higher current CO2 emissions. Life-cycle emissions including manufacturing is important for EV technology, and we should focus on reducing manufacturing emissions as well as cost in battery manufacturing. More detailed (and actual) calculations are needed to determine a credible evaluation of manufacturing-related emission comparison between EV and hybrid cars.

Right now the nice-looking graphs in the report have a margin of error that would make any picture meaningless when including manufacturing-related emissions, besides being wrong (overly pessimistic).

The heading should be “Greener Grid to Reap Benefits of Electric Cars”—the word Needed is wrong in most cases in the figures above.

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By Foo
on August 14th, 2013

@Brandon:  Next time you make a fool of yourself ripping on my “rambling” post, it’d be helpful to first check to see if, as the authors agreed, I in fact identified a methodological error in their paper (and no one else has so far as I can tell).

Anyway, back to the authors of the study: a 50/50 mix of gas and electricity is far oversimplistic and completely unreasonable because it gives a huge advantage to plug-in hybrids with tiny batteries.  No wonder you got the absurd results you got.  Specifically: The Volt goes about 38 miles on a charge, which is well over the average distance Americans travel in any given day.  That was GM’s goal.  For the Volt, a reasonable model might assume that 85% or 90% of the time is spent on batteries. On the other hand, the Plug-in Prius can only get 10 miles per charge, if you’re lucky, and that’s with the gas engine often firing up while you’re supposedly driving on batteries because the battery can’t provide sufficient power.  For this a reasonable model might assume that the battery is only used perhaps15- 20% of the total time.  The C-Max Energi might be about 30-50%.

Because you have made the same assumption for all the plug-in vehicles despite their different battery sizes, you wind up with the situation where the Plug-in Prius performs best in show where the Volt lags far behind, which is ludicrous on its face to anyone with experience with these vehicles.  I think it’s time you revise your model.

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By Foo
on August 14th, 2013

@Lewis:  “any and every saving of fossil fuel by the use of EVs are, like those of the expanding non-fossil energy supply technologies, promptly negated by that same volume of fossil fuel being bought and burnt elsewhere.”

This is magical thinking, and its logic is so broken as to not deserve further response.

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By Chris (Boston, MA)
on August 14th, 2013

Exxon couldn’t have said it better, themselves.  Nice headline “Hybrids better than Leaf…”, then a cherry pick of the 52mpg hybrid Prius.  Gosh, I didn’t know hybrids averaged 52mpgs?  I guess I dispute less that a Prius releases 27 pounds of CO2, per gallon, than I do the 50 state EV CO2/mile assumptions. 

For instance, the study put MA and GA at the same .45lb CO2/mile, while MA used 6% coal to GA’s 33% coal, in 2012.  Natural gas use was used more in MA, but not enough to yield the same number.  It’s bad enough they even arrive at that value because .45lb CO2/mile works to a CO2 rate of 1.32 pounds per kwh, using the Leafs 34kwh/100miles EPA rating.  If you take MA’s actual emissions, as suggested by 6% coal, 69% natural gas power (.79lb/kwh), you get .27lb CO2/mile (just over half the Prius’ pollution).  And we’re to assume the other .18 comes from some methodology of fuel production?

I call BS on this article because the fact is carbon intensity has stark contrast between the five worst states, emitting over 1,500lbs/mwh, and the 31 that don’t even get to 1,000lbs/mwh.  Prius owners who want to get on a stump (w/Exxon) should also consider that EVs, and hybrids, tend to sell best where coal is used least.  Acknowlege that before tooting your horn and promoting CO2.

and 69% natural gas, in 2012, versus Georgia’s  

For instance, how can MA, at 3% coal use in 2012, be

No credible CO2 vehicle comparison comes without stated assumptions for CO2 per gallon, or kilowatt hour.

Electricity is grossly cheaper than oil.  So much so, that the combined United States revenues across residential, commercial and industrial use, don’t add up to Exxon’s, alone (<400 billion vs ~470 billion).  The propaganda cash that spills over to promote these shallow one-offs, and protect profits from the almighty $4 gallon, should never be underestimated.

I drive a PHEV and make no pretense about it being as good for CO2 as clean an EV.  The all-coal outlets that could begin to substantiate your conclusion, are a practical myth.  Per EIA, coal was 37% of the US, and if you look at agregate kwh sold, per state, by fuel, which is ALL AVAILABLE AT EIA.GOV, you will see most of those grey states top out at 60-80% coal.  But, of course, this article has no correction factor for other fuels

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By Lewis Cleverdon
on August 14th, 2013

Far from being broken, this logic is evidently beyond any refutation you can offer.

The magical thinking is by those who want to maintain the comforting delusion that
because a driver buys an EV and no longer buys 10gls of gas per week,
that gas somehow has no value and will not be bought and burnt by anyone else
even at a marginally lower price.
And if magically no one in the US wanted it, then maybe a little less would be imported,
but somehow that same amount wouldn’t be bought and burnt elsewhere in another country,
despite the booming car sales in many developing countries.

That magical thinking may be great for building a self-gratification EV club on the fallacy
that “we’ve helped to cut CO2 emissions”
but by distracting effort from pressing for a commensurate treaty
- which is the only means of halting the bought-& burnt-elsewhere syndrome -
it is harming the prospects of mitigating AGW.

But then if you actually took the issue of AGW as seriously as it warrants,
you’d no doubt have worked this out for yourself.



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By Joshua Tulberg (Emeryville/CA/94608)
on August 15th, 2013

Finally got around to reading the entire PDF, I enjoyed it, but here are a few things that bother me:

They make no mention of % Population, merely # of States. According to their (PDF) map, there are 13 states (yet “18” according to the map on the top of this page) where a (100K mile) leaf is better for the environment (including manufacturing). I checked it, and these 13 states make up about 31% of the Population. (The 18 states make up about 44%)

They then go on to say (page 15) that if a leaf were to be driven 200,000 miles it would best the Prius (including manufacturing) in “only” (<—!?) 23 states. (They didn’t bother to mention which states, but I could only imagine it was the ones shaded “light-green” (The one’s that were on the verge), which would put the % Population way in favor of EV’s)

They include a 50K mile map (which seems quite pessimistic), and they include a 100K mile map because: (page 15) paraphrasing: “That’s what the batteries are warrantied to”, but they neglect to include a 150K mile map.

They mention (page 26 <—!?) that this paper represents “merely a snap-shot in a moving picture”. Ok… but perhaps they should have ended it with some sort of prediction or trend-analysis, especially considering:

(page 1) They mention that in just 2 years (2010-2012) the Grid’s CO2 emissions were reduced 8%, which doubled the # of states for EV’s.

So basically, even this “snap-shot” which would have you believe that a Prius bests a Leaf would be lost in time if:

- You drive your EV more than 100K miles
- The grid gets any cleaner

Something tells me both of those are going to happen.

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By Joe (Montpelier, VT 05602)
on August 17th, 2013

Why is the all-electric Mitsubishu MIEV not included in this article?

I’ve been driving one for a year. I use it for my work, it was more affordable than the Leaf and the Volt, and I’m quite happy with it so far.

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By Assaf Oron (Seattle/WA/98115)
on August 19th, 2013

I have just spotted a possible discrepancy that biases the analysis against EVs. It is buried in the comments and referred-to articles, so please bear with me.

As the authors admit, on a point-of-use analysis of miles-driven only, EVs are already better than the best hybrid on average.
The problem is they need to overcome a deficit generated when the battery is produced. The authors have taken Hawkins et al (itself if I’m not mistaken, a study carried out by an oil-industry-supported university, but I digress). However, they *modified* the Hawkins et al. methane contributions from a 100-year impact (which is the standard, used e.g. in IPCC reports), to a 20-year impact. As the authors say, this has *increased* the overall production footprint estimate for the Leaf by 12% (footnote 13, p. 25). No chump change.

On the other hand, the authors cite the Burnham et al. article out of Argonne for calculating the gasoline wells-to-wheels overhead, which according to that article is a measly 35% (6.9 lb/gallon on top of the 19 lb/gallon base; p. 24 and footnote 6). I took care to actually *read* Burnham et al. Guess what? That article calculates the rather substantial methane flaring overhead in oil production, using the *100-year* impact.

So what do we have here? The biggest overhead to EVs is calculated using the assumption leading to a higher estimate, while the biggest overhead to gasoline is calculated using the lower estimate.

Can Climate Central look into this discrepancy, and fix it and issue a correction if needed?


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By This study lies
on August 19th, 2013

The Prius Plug in’s 11 mile EV range isn’t even pure EV, it is blended.  The Volt’s 38 (non blended) EV range allows people to drive way more electric miles.  There is no way the average Prius Plug in driver drives anywhere near as many electric miles as Volt drivers.  The report grossly exaggerates how many charge sustained miles Volts need. 

Next, the report neglects how much energy is used to drill and transport crude, and how much electricity is used to refine it.  Search the report for keywords such as “refine” and “refinery”. 

There is no examination of when people are charging, and how off peak hours are easily used.  Search “peak” and “night”.

They did an amazing job of cherry picking the data and making the wrong assumptions for it.  Here is another perspective, comparing Leaf and Prius:




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By Marc (04074)
on August 23rd, 2013

This so-called comprehensive and exhaustive (to read) study not only made no mention of the very large carbon footprint of all aspects of gasoline production, it also failed to mention many EV owners (about 30%) including myself provide power for their cars with ‘residential’ photovoltaic systems (solar panels).  Life Cycle Assessments are complex and can be ‘manipulated’ to suit arguments pro and con.  I feel the emphasis should be on the ‘in phase’ carbon emissions of EV’s which overall are the most climate friendly and most certainly if one uses the power of the sun!

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By Jack Lucero Fleck (Oakland, CA 94619)
on August 23rd, 2013

Thanks for your report.  I found a lot of useful information in it.

Question:  What is the right number for CO2 equivalents produced by the Prius
1.  331 grams/mile (Table 5 shows 0.73 lbs/mi = 331 g/mi)
2.  306 g/mi Table 4 shows 33.7 tons of ghg for 100000 miles = 306 g/mi
3.  311 g/mi Using 25.9 lbs of ghg/gal x 46.3 mpg = 254 g/mi for driving plus Table 9 15627 lbs for the car for an EPA estimated life of 120,000 miles = 59 g/mi for a total of 311 g/mi

Here are my more complete thoughts on the report:

1.  The real problem with Climate Central’s Roadmap to Climate-Friendly Cars

Those of us who own electric vehicles are accustomed to hostile and usually ill-informed comments about electric vehicles from the oil company dominated media—e.g. Fox News and the like.  However, I have to admit that I was startled on August 9 to read a front page report in the San Francisco Chronicle declaring “Jolt to Electric Cars:  Hybrids may be the greener choice.”  Specifically the article makes the case that EVs are not as clean as the Prius; the article was based on a report from Climate Central—A Roadmap to Climate-Friendly Cars.

This is not a new claim in the case of electric vehicles operating on heavily coal generated electricity compared to a Prius.  But Climate Central makes a more extreme claim—namely that the Prius is cleaner than an electric vehicle in all but “a handful” of states.  I found this hard to believe, so I delved more into the Climate Central case.  I learned that the claim is based on some reports about the high level of greenhouse gases emitted in the production of lithium-ion batteries and some questionable assumptions about battery life.

The studies used by Climate Central reported that the energy and resource intensive process of manufacturing batteries for a Nissan Leaf produces 11,516 pounds of CO2 equivalents of greenhouse gases (ghgs). This is 19% higher than an April, 2013 EPA study’s estimate for ghgs created in battery production. The Climate Central figures result in 104 grams of CO2equivalent per mile if batteries last 50,000 miles, and 52 grams per mile if they last 100,000 miles.

But how long will EV batteries last?  Is the Climate Central assumption of 50,000 - 100,000 miles realistic?  This assumption is contrary to the findings reported by Forrest Jehlik of the Center for Transportation Research. .  Jehlik has tested the current generation of lithium-ion batteries, testing cars for more than 150,000 miles. Even at the end of the car’s life, the vast majority of batteries still function quite well, Jehlik said. “When these cars become available for sale, the batteries are going to last as long as any part of them will,” he said. The Climate Central assumption is also contrary to the EPA’s April 2013 report, which uses the full life of the car estimated at 120,000 miles for the life of the battery. 

Note:  to see more detailed calculations and discussion of all of the numbers used in this article, please see the blog Solar Power & Electric Cars.

Using 120,000 miles for the battery life, the Climate Central figure for ghg’s from batteries is 43 g/mile.  The EPA’s figure is 35 g/mile.  Either way, this is still a significant number— it raises the ghg’s for EV production to 92 - 100 g/mile.  Driving an electric car on the standard U.S. grid produces about 200 g/mile, bringing the total ghg for an EV to around 300 g/mile.  Using the 120,000 mile figure for the battery means that an EV powered by the standard grid is still a bit cleaner than a Prius (330 g/mile).

The Climate Central study does note that the grid is getting cleaner as coal plants are being closed (8% improvement from 2010 to 2012), and that EVs are becoming more efficient (citing a 15% efficiency improvement in the Leaf).

The Real Problem with the Climate Central Report

So, while the Climate Central report is a bit off in terms of its claim that the Prius is cleaner than an EV, the real problem with the report is deeper than that.  The real problem is that the report does not address the issue of what is needed to stop climate change.  The fact is that there is no way that either hybrid vehicles like the Prius or EVs running on electricity generated by fossil fuels can begin to be clean enough to lower CO2 by the 90%+ needed stop the build-up of CO2 in the atmosphere.

The only hope for stopping global warming is to convert to 100% EVs running on 100% renewable energy. 

This is the only way to stop CO2 from continually building up in the atmosphere. (I’m assuming that the option of building all U.S. cities to the density of Manhatten, where transit is more viable and automobiles are much less needed, is not a realistic alternative).  Even clean options like the Prius, or EVs running on electricity generated by natural gas will not stop the build-up of CO2.  Two plans supporting EVs running on renewable energy as a necessary solution to climate change come from Mark Jacobson and Mark Delucchi (Part 1 and part 2)  Also, this Science magazine article by eight researchers comes to the same conclusion.  I’m not aware of any serious plan to halt global warming (i.e. one that at least cuts CO2 to 80% below 1990 levels by 2050) that continues to use fossil fuels for electricity production or transportation.

Given the new numbers including ghg’s produced in battery manufacture, an EV running on wind or solar would produce ghg’s in the range of 110 g/mile.  Compared to 536 g/mile for an internal combustion engine vehicle, that is a 79% reduction. This is not a pipe dream—Santa Monica reports that 30% of EV owners have solar panels on their roof.  I have also heard estimates as high as 40% of EV owners in California using solar power.  However, although 79% is a great improvement, it is not enough to stop global warming.

In this regard I find the EPA report quite encouraging regarding prospects for making EV batteries cleaner.  The authors speak of ways to improve the ghg’s created in the production process, and ways to improve recycling of the batteries.  Ironically, I felt that the EPA reporters are more aware of the urgency of finding ways to improve the cleanliness of the batteries than the Climate Central reporters are.

The Climate Central website describes the organization as follows: “An independent organization of leading scientists and journalists researching and reporting the facts about our changing climate and its impact on the American public.”  Unfortunately Climate Central’s Roadmap takes us to a dead end.  Whether a Prius is cleaner than an EV running on electricity from coal is a moot question—either way we end up with a planet that is toast.  Climate Central presumably agrees that it is a fact that there is an urgent need to drastically cut CO2 to prevent the worst impacts of climate change.  It is also a fact that the necessary cuts can only be accomplished by converting to renewable energy and using that clean energy to power electric vehicles, especially those built with more efficient methods than at present.  Hopefully Climate Central will incorporate such a recognition in their future reports.


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By Andrew (Eugene, OR 97403)
on August 24th, 2013

Earth to Kevin in So. California, nuclear power IS NOT “essentially carbon free”, unless you eliminate the fuel it uses to power these plants, enriched uranium.  This fuel is mined, and leaves most communities it is extracted from permanently damaged from the lack of clean up.  It is transported to the one facility in the US that will enrich it in Kentucky and guess what, the enrichment process is done in a COAL FIRED PLANT.  Then, it has to be transported back out to the 104 leaky nuclear plants around the country.  The transportation to and from this plant is NOT carbon neutral.

Shuttering San Onofre was the best thing to ever happen in So. Cal, since this plant was incredibly built on an active earthquake fault.  Think Fukashima was bad, it would pale in comparison to a major earthquake hitting the San Onofre plant. 

As for the inflated 25% power generation figure from PG&E that the plant produced for the area, retrofitting a half million homes with PV solar panels in So Cal would take care of that loss. The solar array on my house produced 8-900 kWh per month and will pay for the cost of the system in 5-6 years. 

PG&E also warned us that there would be major black outs occurring last summer because of the shut down, which NEVER HAPPENED.  Don’t be fooled by the nuclear industry propaganda.  It is a brilliant, but fatally flawed technology which is far from carbon neutral.

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By ted rees (Mountain view, CA 94040)
on August 28th, 2013

  After reading the report, and the blogs, It all seemed confused. The data forming the basis of the conclusions seemed confused. Is there some way to clarity?
  First of all, we have all been burned by the assumption that CO2 from fossil fuels somehow was not important. Now it seems that CO2 will likely persist in the atmosphere for thousands of years, pulling the earths temperature toward a temperature many degrees warmer than it is now. Alligators in the arctic. So, any added CO2 burning is not justified, and instead we actually need to remove CO2 from the atmosphere.
  Higher efficiency cars help reduce CO2 buildup, but we need zero CO2 producing cars. That will only come from EV cars that are charged and built with renewable energy.
  And in addition to that, we need to pull the excess CO2 from the atmosphere and put it back underground.  How bad can it get?

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By Sterling (Houston/Tx/77077)
on September 4th, 2013

I wonder how much Toyota contributes to “Climate Central”? Logo’s are essentially the same. Perhaps this organization could be more credible is they were more transparent about who, especially which auto manufacturers, are contributors.

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By Dan Yawitz, Alyson Kenward, Eric Larson (Climate C
on September 6th, 2013

In the month since we released our report, A Roadmap to Climate Friendly Cars: 2013 we have received many good questions and insightful comments from readers. Thank you to everyone who has taken time to give us feedback. We especially appreciate those who recognized the inherent challenges involved in carrying out and presenting lifecycle analyses. Our research team has reviewed all of the reader responses, and here we offer some additional thoughts and clarification to address those comments.

    - Several readers thought that for gasoline we considered only the emissions from combustion and not the full lifecycle emissions (including emissions during oil extraction, transportation, and refining). As we wrote in the report, we did consider the full lifecycle emissions for gasoline. To do otherwise would not be an apples-to-apples comparison.

    - One reader thought we had used a 20-year GWP when assessing electric vehicle emissions and a 100-yr GWP for assessing gasoline vehicles. In retrospect, our report is not clear on this point, so the confusion was understandable, but in fact we applied 20-yr GWP values for ALL vehicles analyzed. To do otherwise would have been an unfair analysis.

    - Several noted that for plug-in hybrids we assumed that these cars drive half their miles on gasoline and half on electricity, but you also believe that many plug-in owners don’t drive their cars this way. Driving behavior certainly does make a difference in total emissions generated while driving plug-in hybrids. However, we are not aware of good data that show on average what the mileage splits are on electricity and on gasoline for different model PHEVs, so we decided to keep it simple. But, in our 2012 report on climate-friendly cars, we did evaluate the impact on emissions of different driving behaviors with the Chevy Volt, and we referred readers to that report to get some idea of how the driving splits affect emissions.

    - One reader said our report was confusing and, apparently, self-contradictory. Aside from a couple of typos (which we have fixed), it is self-consistent, but admittedly we could have been more explicit when distinguishing between what we called emissions associated with “driving and charging” a car and the “lifecycle” driving emissions. The latter is the appropriate one for comparing the overall climate-friendliness of vehicles. We presented the former to help highlight the differences in electricity generation mix between states.

    - Several pointed out that as the grid mix changes in the future, so too will the emissions of electric vehicles. Absolutely. And we hope that the grid mix will evolve to lower and lower carbon sources. In our report we noted this was the trend from 2010 to 2012, but we also noted that coal use was on the rise again in early 2013. Since it is difficult to make predictions (especially about the future), we decided to present a “snapshot.” We will show another snapshot next year, and we hope that will show further improvement.

    - Several mentioned a lack of uncertainty analysis. We acknowledge that we could have more clearly illustrated the sensitivity of lifecycle emissions to different input assumptions. 

For example, some readers pointed out manufacturing emissions for the battery as a particularly important parameter. There is a wide disparity in the literature on estimates of battery manufacturing emissions. There are also not very many detailed and well-documented studies published on this. We chose to base our analysis on Hawkins’ work (including a correction he published this year on his earlier, better known, work) because we found his analysis quite detailed and well documented. But we also did some internal calculations to check the sensitivity of our findings to the assumed battery manufacturing emissions. We found that they have a relatively small impact on the Leaf vs. Prius state-by-state rankings. Moreover, the impact of the battery manufacturing emissions decreases as the assumed lifetime driving miles increases, as one would expect.

Several noted that the time of day when a battery is recharged from the grid will have an impact on emissions. We acknowledged as much in our report, but we decided to use annual average emissions from electricity generation because we did not find data that would allow us to say with much confidence what the average charging behavior of the average electric car driver is.

A few readers noted that if charging is done from a solar panel, emissions would be very low. We agree, but chose not to evaluate the “off-grid” option, since there are insufficient data on how many electric car owners recharge in this manner. Also, as the number of electric cars on the road increases, an increasing fraction will be charging from the grid, so we felt grid-connected recharging was of broader interest and relevance.

There were additional comments about our not showing lifecycle emissions for lifetime car mileage above 100,000 miles. We are not aware of good data on what actual EV car lifetimes are, probably because there is not enough experience out there yet to say with much confidence. This is why we limited ourselves to 100,000 miles. However, we did note that emissions per mile for electric cars improve the further they are driven, and we also mentioned that if a car lasts for 200,000 miles without the need for a battery replacement, we find that the best EV (Honda Fit) is more climate friendly than the best hybrid (Toyota Prius) in 26 states (and, for those interested, at 200,000 miles, the Nissan Leaf is more climate friendly than the Prius in 23 states). 

    - At least one reader pointed out that despite disagreements you have with some of our assumptions, an important underlying conclusion of our analysis is that for electric cars to improve their carbon footprint, lower-carbon grids are needed, and emissions associated with manufacturing the vehicles is needed. We agree.

    - Another reader asked, “What is the right number for CO2 equivalents produced by the Prius?” and proceeded to calculate three different answers starting with numbers taken from different tables in our report. In fact, there is only a single number, which we can arrive at via all three of your calculation methods, if we correct the mistakes you made.

Here are our corrections:

1. Emissions for Prius in Table 4 are 0.67 lbsCO2e/mi (not 0.73 that you used). This converts to 304 g/mile.

2. We agree with your calculation #2, which gives 306 g/mi.

3. The Prius fuel economy according to EPA (combined city/highway drive cycle) is 50 mpg, which we show in Table 2 (you used 46.3 mpg for your calculation). Also, the vehicle manufacturing emissions (15,627 lbsCO2e) should be divided by 100,000 miles (not 120,000) to put it on the same footing as your calculations #1 and #2. With these corrections, calculation #3 gives 306 g/mi.

    - Finally, it was noted that carbon offsets could be purchased from TerraPass to eliminate the “carbon debt” due to manufacturing of the battery of an electric vehicle. Presumably this could be done to offset a vehicle’s driving-related emissions, as well. However, if everyone just buys offsets and continues to drive carbon-emitting cars, it will not accomplish much toward solving the climate change problem. A low-carbon grid and less polluting manufacturing processes are needed for that.

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By Jake (Shawnee, KS 66203)
on September 9th, 2013

This is a great study!  Could we see something similar for battery powered plug - in lawn mowers and motorcycles, compared to their gas counterparts?

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By Ann (Columbia,MD 21045)
on September 9th, 2013

This article is worthless tripe.

This study does not take into effect that I can get all my electricity from wind power. Therefore, the notion that my energy in MD is so bad, and gas is better, holds no water.


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