US Mitigation Math
March 9th, 2009Posted by: Roger Pielke, Jr.
The mathematics of United States carbon dioxide emissions are not actually that complicated. The figure below from the U.S. Energy Information Agency shows that the 5,991 million metric tonnes (MMt) of carbon dioxide emitted by the U.S. came from 3 sources: coal, natural gas, and petroleum (see three inputs in the upper left of the graph).
Each of these fossil fuels, plus renewables and nuclear power make up the total energy consumption in the United States. Energy consumption is measured using a unit call a “quad” which means a quadrillion BTUs (British Thermal Units). In 2007 the United States used 101.4 quads of energy (data). This amount of energy can be broken down by source as follows.
The 15.2 quads of energy from nuclear and renewable sources resulted in negligible carbon dioxide emissions. The amount of carbon dioxide emitted due to each quad of fossil fuel energy depends upon the source, as their carbon intensities differ. For the analysis that follows I use the following values, distilled from the EIA information provided here in .xls.
Coal = 94 MMt Carbon Dioxide per Quad
Natural Gas = 53 MMt Carbon Dioxide per Quad
Petroleum = 65 MMt Carbon Dioxide per Quad
Thus, to calculate total U.S. carbon dioxide emissions simply requires multiplying quads of energy by carbon dioxide per quad and summing across the three fuels. This simple math results in the following:
(94 * 22.8 [Coal]) + (53 * 23.6 [Natural Gas]) + (65 * 39.8 [Petroleum]) = 5,981 MMt carbon dioxide
This total compares quite well with the total of 5,991 MMt carbon dioxide reported for 2007 by EIA (see figure above). We can use this information to ask some straightforward questions about how an emissions reduction target of 14% below 2005 levels (5,095 MMt carbon dioxide) might be reached by 2020.
We can do a bit of hypothetical “stress testing” of these numbers, by asking, in theory, what sort of actions might lead to reaching the emissions reductions target. Before we do this, we do need to make a guess as to 2020 US energy consumption. The EIA projects that energy consumption will grow at a rate of 0.5% per year (calculated from information here). Because GDP growth is expected to be higher than this rate, it already builds in an assumption of gains in energy efficiency. But let’s use the EIA estimate, which suggests that US energy consumption in 2020 will be 108.6 quads, of which 21 quads will come from renewables plus nuclear energy, representing a growth of about 40% on top of 2007 values. This leaves 87.2 quads to be produced by fossil fuels.
Here are a few examples of the effects of different hypothetical strategies:
1) What would happen if all coal consumption were to be replaced with natural gas?
Answer: In 2020 total emissions would be 5,110 MMt carbon dioxide, very close to the 2020 target.
2) By how much would renewables plus nuclear have to displace coal to reach the target?
Answer: The target could be reached if coal consumption were reduced by about 42%, and the displaced 9.2 quads of energy were replaced by renewables plus nuclear, implying more than doubling of renewable plus nuclear energy supply, to comprise 30% of all energy consumption.
If renewables alone (i.e., non-nuclear) are to carry the weight of displacing coal, then they would have to increase their role in consumption by a factor of 4.7 over 2007 values. If growth in renewable energy supply is restricted to solar and wind only, then these sources would have to increase their role in consumption by a factor of 80 (that is, e-i-g-h-t-y). The reason for this big difference is that biomass and geothermal provided about 6.4 quads of energy in 2007, whereas wind and solar only 0.4 quads. The Obama Administration’s goal of doubling wind, solar, and biofuels production within 3 years may indeed be a worthwhile policy, but it is not consistent with a goal of displacing sufficient coal to reach the 14% 2020 target using wind and solar (and while biofuels have their own complexities as a policy issue, they are not really a substitute for coal in any case).
3) By how much would energy consumption have to be reduced to meet the target assuming no changes in the energy consumption mix?
Answer: Energy consumption would have to be about 85.5 quads in 2020, about equal to 1992 values when the US economy was 35% smaller than in 2007.
Some Comments on the Stress Tests
First, number (1) above is really not desirable if the goal of mitigation policy is ultimately a reduction in emission of 80% or more. The reason for this is that while natural gas is less carbon intensive than goal, it is still carbon intensive. Locking in a large natural gas infrastructure is not compatible with large emissions reductions. Consider that in the hypothetical case that all US fossil fuel needs were to be met by natural gas, then 2007 carbon dioxide emission would have been 5,375 MMt, less than observed in 2007, but not consistent with any low stabilization target.
Second, number (2) is theoretically promising but practically daunting. The following is worth repeating — for wind and solar to displace enough coal to reach the 14% target by 2020 would require that it increase by a factor of 80 in absolute terms from 2007 production. President Obama’s policy of a tripling in wind and solar energy supply in the next three years would leave a need for another increase by a factor of about 25 over the next 8 years if wind and solar are to displace sufficent coal to meet the target.
Third, with respect to number (3), while there is a lot of potential to exploit in increasing energy efficiency, to reach the 14% would require a reduction of US energy use by about 2 quads per year for the next decade. Assuming that policy makers and citizens want economic growth to resume, this is a Herculean task. If you factor in that the EIA estimates to 2020 already include a good bit of efficiency gain in the BAU scenario, the task could be even larger if these assumed gains do not occur or if economic growth happens at a faster rate than assumed.
In reality, of course, none of these “stress tests” would be applied alone; there would be a combination of all three approaches discussed above. However, I challenge readers to present a scenario combining decarbonization of the energy supply and efficiency gain that has a realistic chance of succeeding in meeting a 14% emissions reduction (below 2005) by 2020. I am not saying that it can’t be done, but I am saying that I don’t see how it can be done. The comments are open, have at it.
Setting an emissions target and timetable, allocating emissions permits, and then saying that the magic of the market will efficiently take care of the task is exactly the answer I’d expect if one doesn’t have an answer. Markets can’t make the impossible possible, and when they are used in such a manner, often have undesirable results.
March 9th, 2009 at 9:52 am
Wouldn’t it be appropriate to “value” this exercise. That is how many fewer ppm of CO2 will there be in the atmosphere in say 2050 and 2100 as a result? This being analogous to return on capital employed.
March 9th, 2009 at 10:12 am
-1-maurmike
“1 ppmv of CO2= 2.13 Gt of carbon”
http://cdiac.ornl.gov/pns/faq.html
*to convert to CO2 . . . 2.13 * 3.664 = 7.8 Gt CO2
*so for 2020, under the EIA assumptions (in GtCO2):
6.225 – 5.095 = 1.13 GtCO2
1.13/7.8 = 0.14 ppm in 2020
March 9th, 2009 at 11:08 am
Therefore a huge expenditure will result in about 4ppm reduction in 2050.
March 9th, 2009 at 11:15 am
Your 3-path decomposition is merely an argument that, if none of us sitting at the table at a restaurant can pay the full bill for everyone, we shouldn’t order. You conveniently change the units of measure from % terms (which make emerging supply technologies look bad) to absolute quad terms (which make technologies with a large base look bad) when it suits the argument. You also ignore the fact that the options interact nonlinearly, i.e. #3 makes #1 & 2 easier to swallow.
It’s useful to have some general bottom-up idea of the feasibility of a target, but to imagine that detailed plans can be accurately made, let alone carried out, or could be promoted by a multitude of sectoral measures, is greater folly than trusting markets.
Nevertheless, you don’t need to make your poor readers come up with a plan. You could find dozens of them in EIA reports ( http://www.eia.doe.gov/oiaf/1605/climate.html ), the SRES database, and elsewhere in the literature. Even the most neoclassical economists think a 20% reduction is not impossible, nor even particularly costly.
I think if you wait a couple years, your analysis becomes true regardless of my quibbles, because we are nearing the point at which capital turnover is a serious constraint. If cap & trade is the instrument, then we’ll eat those couple of years negotiating the market structure. Because short term energy demand is inelastic, yet a lot of environmentalists and the financial markets hate the idea of a safety valve, policy makers will either have to risk a permit price train wreck, or set a wimpy target. I’m guessing the latter.
March 9th, 2009 at 11:17 am
This is why substantially increased bio-sequestration of CO2 is a solution that needs more serious attention:
New forests on the Sahara and Australian Outback, IRRIGATED with reverse osmosis water from the oceans, could sustainably, safely and ‘forever’ sequester a net of about 8 GtC/yr (28,000 MMt CO2/yr)! This will take decades to implement, but the required technology is developed and mature.
And if newly fallen trees in the old-growth tropical forests of the Amazon and Congo were CAREFULLY and regularly harvested, instead of ‘being allowed to’ rot, another few GtC/yr of respiratory CO2 would fail to enter the atmosphere. This kind of harvest could begin on a large scale, almost ‘overnight’!
Note that renewable wood could quickly and sustainably replace coal, and also gradually replace the non-renewable oil and gas, which are being depleted rapidly – but only if population growth levels off.
Let’s think outside of the box for a change!
March 9th, 2009 at 11:52 am
Back in the glory days of the tech bubble, start up companies would put together a plan showing a hockey stick shaped income curve that started up after the company received a few million dollars in investments. The math was always right but the assumptions were carefully selected to shape the chart. It’s always easier to shape a chart than to shape the future.
To make the math of CO2 emissions work we just have to examine the underlying assumptions. The following starts off the same as the post and only changes assumptions to make the math “work”.
2007
Source quads CO2/quad MMt CO2
Coal 22.8 94 2143
NatGas 23.6 53 1251
Petroleum 39.8 65 2587
Renewable 6.8 0 0
Nuclear 8.4 0 0
==== =====
101.4 5981
1. Assume that a one trillion dollar carbon tax in the US stalls economic growth.
2. Assume that the tax is applied to all US products and not to Russia, India, or China. This assumption leads to a 6.6% decrease in US GDP and a corresponding increase in GDP for other countries that have a competitive edge.
3. Assume that total energy usage is linear with GDP.
4. Assume that for some portion of the $1T energy from renewable sources can be increased 80% from its low current base.
5. Assume that permits are allowed and Nuclear power can be increased by 10%.
2020
Source quads CO2/quad MMt CO2
Coal 19.4 94 1823
NatGas 20.1 53 1065
Petroleum 33.8 65 2197
Renewable 12.2 0 0
Nuclear 9.2 0 0
==== =====
94.7 5085
These assumptions have the math working and the US meeting the internal goal of CO2 reductions. However that’s not a good thing. Aside from the lower quality of life here in the US, we are more efficient in converting energy to GDP that the rest of the world and the global result would be more CO2 emissions.
Anyway this math is just for the cost. Cost is only half of a cost/benefit analysis.
The benefit assumes some reduction in global warming for a reduction in CO2 emissions as projected by the IPCC climate models. This only works with some more assumptions.
1.The climate models use the assumption of a positive feedback from water vapor. Change this assumption to a negative feedback and the benefits decrease by about a factor of four.
2. The global reduction in CO2 is based on the assumption that Russia, China, and India will also reduce their emissions. (This is more wishful thinking than assumption.) Change this to assume that those three countries will act in their own best interest and global emissions will increase.
Math pffft. What could be motives be for such a plan that even a bunch of bloggers can discredit?
March 9th, 2009 at 11:53 am
Sorry about the alignment. It was all straight on my preview.
March 9th, 2009 at 12:17 pm
How about this strategy (not that I favor it, but it may be politically likely):
No new coal power plants (they will become harder to get approved than nuclear during the 90s). Required energy replaced by nuclear and renewable as much as possible, and natural gas as needed. Resulting higher electricity prices restrain demand.
Transportation (using petroleum) efficiency roughly doubled (nearly complete switch to hybrid cars, high gas prices and European gas tax levels). Long haul trucking and rail switch to natural gas and electric (electric for 50% or more of rail).
Industrial use of petroleum cut in half (25% replaced by NG, 25% shifted to foreign sites).
I have not had time to analyze the savings, so I welcome corrections and a good estimate on the effect of no new coal power plants.
March 9th, 2009 at 12:33 pm
-4-tomfid-
Which one of those EIA spreadsheets has a 14% reduction by 2020?
The most recent analysis of Lieberman Warner April 2008 has 5,587 MMt CO2 for 2020.
March 9th, 2009 at 1:43 pm
Re 2
You need to account for dynamics of the carbon cycle. Atmospheric retention is very roughly half, so the difference amounts to .07ppm per year in 2020. The cumulative effect is larger, but depends on the future trajectory of other emissions.
The value you assign to that is heavily contingent on whether you value impacts outside the US, and whether you think others play along.
There isn’t much evidence that this size of cut results in a “huge expenditure” once you net out energy savings from capital costs, especially if your yardstick is the stimulus.
March 9th, 2009 at 2:10 pm
Re 9
The EIA tests aren’t as deep (13% from BAU for the S.280 analysis) but they also don’t do much to prices or shares, so it seems fair to presume that they’re not pushing the envelope. However, they cheat, using lots of international offsets, so maybe they aren’t the best example. But if you look at other models, there are still plenty of options. On the other end of the spectrum from NEMS, in DICE you can do it for less than half a percent of GDP. I think most 450ppm scenarios, including MiniCAM, get roughly there – which means fairly high carbon prices, but far from impossible.
The stupid thing about a hard quantitative target is that if you’re wrong by 1% about what’s practical (i.e. quantity achievable at some price you think won’t give voters a heart attack) you’re wrong about the market clearing permit price by 10% in the short run. Since the EIA BAU could easily be wrong by a lot more than that, that’s an invitation for the system to unravel due to short term pressures that have nothing to do with climate.
March 9th, 2009 at 2:19 pm
tomfid,
Others will not play along because the hysteria over global warming is purely a rich country obsession and is of no interest to countries with large populations of poor people without access to the basics. The current economic downtown will also make it polictically difficult to transfer billions to poor countries in order to bribe poor countries into pretending to reduce emissions.
Also, I don’t see any evidence that a transition from low capital/high energy density sources like coal to high capital/low energy density sources like wind/solar will result in any ‘capital cost savings’. If anything, the capital costs will go up even if energy production declined.
March 9th, 2009 at 2:43 pm
I’m afraid I don’t have time for an extensive post, but may I ask whether the limiting of the list of proposed suggestions to three suggests that you reject Pacala & Socolow’s concept of multiple stabilization wedges (seven in their original proposal, though others have suggested addition of even more)? E.g., http://www.princeton.edu/~cmi/resources/stabwedge.htm
Large scale mitigation will not occur spontaneously (unless, of course, you’re the IPCC), but it is hard to visualize significant mitigation coming from concentrating on only one or two sectors, as opposed to the multi-facted approach envisioned by Pacala & Socolow, where a number of different strategies are pursued simultaneously (and including a big wedge of efficiency).
March 9th, 2009 at 2:58 pm
“New forests on the Sahara and Australian Outback, IRRIGATED with reverse osmosis water from the oceans, could sustainably, safely and ‘forever’ sequester a net of about 8 GtC/yr (28,000 MMt CO2/yr)! This will take decades to implement, but the required technology is developed and mature.”
Do you have any technical and economic analysis for this concept?
For instance, I assume the albedo of a forest would be much lower than the sands of the Sahara (and Australian Outback), so wouldn’t that offset the benefits of reduced CO2?
Also, what cost are you assuming to desalinate the water and pump it to the places it will be needed?
March 9th, 2009 at 3:36 pm
Very illuminating indeed! Thanks.
March 9th, 2009 at 4:26 pm
-13-lgcarey
Just a quick response, the stabilization wedges are flawed for the same reason that the IPCC SRES are flawed, due to heroic assumptions of spontaneous decarbonization.
But more generally, the approach presented here shares with the wedge approach an effort to devise to present the scale of the challenge in a simple way. The wedges focused on emissions, the approach here focuses on energy supply. Done properly, both analyses should wind up in the same place.
What we are talking about here is about 0.3 of one wedge (1 GtC) over 10 years (~0.3 GtC). That might help put into context 14, 15 or 20 wedges by 2040.
March 9th, 2009 at 4:35 pm
Rodger,
Could you break out the 6.8 quads of renewable energy into its component parts. I assume this would be solar, wind, geothermal, hydro electric, bio fuel and bio mass. Did I miss anything?
March 9th, 2009 at 4:50 pm
-17-Gorman
From the EIA site linked in the post:
Hydro 2.5
Geot 0.35
Solar 0.08
Wind 0.32
Bio 3.6
March 10th, 2009 at 1:27 am
Roger, do you have any breakdown for how much energy is used in agriculture & food production? UK studies seem to suggest about 25% of UK energy consumption goes into the combination of farming and food production, and this didn’t count the energy involved in packaging distribution and shopping.
March 10th, 2009 at 8:00 pm
[...] Pielke Jr. has an outstanding post titled US Mitigation Math where he shows the general sources and sinks of US energy and resulting [...]
March 10th, 2009 at 8:14 pm
I tried to see if I could reach the reduction goal if I used the Obama administration’s projected $645B from carbon allowance auctions to reduce energy use or decarbonize the supply: http://nearwalden.com/blog/?p=963
March 11th, 2009 at 5:48 am
I would tend to agree with tomfid that for a reader to come up with a viable plan alone could take considerable time, as we are not all experts nor have the time to fully digest all the necessary data to propose such a plan. However, we should be coming to a consensus about what is feasible if it is not 14%.
Reality maybe that 14% is not attainable, but if it is not what is a reasonable number? It is unfortunate that in public policy situations we too often have a ‘single number’ goal, and if we can’t reach it then we revert to the ‘why try’ mentality. So might the better exercise be to determine what values are easily, reasonably, and challenging to obtain and try to work from that perspective?
Roger, I am curious if you have a number you think might be reasonable? I know with an initial post it is sometimes best to leave such thoughts off the table, but now that there is some response I would be curious what your take is.
Certainly any solution is going to involve a mix of processes to achieve the goal, just like when a company sets profit objectives for the year and works towards that objective from all cost and revenue aspects of the business. I personally feel that consumption changes could play a larger role. Having lived outside the US for a significant number of years, I wonder if shifting away from a 24 hour (always open) mentality might not have a meaningful impact on consumption levels? I think there is a fair amount of unneeded consumption that keeps everything going full steam around the clock.
March 11th, 2009 at 2:44 pm
Really valuable information. I have not seen anything like this before.
Regarding your previous response to a commenter:
“1 ppmv of CO2= 2.13 Gt of carbon”
http://cdiac.ornl.gov/pns/faq.html
*to convert to CO2 . . . 2.13 * 3.664 = 7.8 Gt CO2
*so for 2020, under the EIA assumptions (in GtCO2):
6.225 – 5.095 = 1.13 GtCO2
1.13/7.8 = 0.14 ppm in 2020
The bottom line here is a reduction of atmospheric CO2 of 14/100’s, correct?
Based on current climate model sensitivity, what would be the temperature reduction of this outcome by 2020? Is there a way to estimate the dollar cost of this project(s) to achieve this?
March 11th, 2009 at 4:57 pm
It would be 0.14/ 1,000,000. After accounting for absorbtion it’s 0.07/1,000,000. The climate impact would not be discernable in 2020 or 2050 for that matter.
March 11th, 2009 at 6:22 pm
Thanks. Yep, I thought it was to be read as 14/100’s of 1 part per million, which is obviously very tiny. Not being a scientist, I just assumed this would have literally zero impact on temps and would require a huge amount of investment to achieve, and an un-godly disruption in economic activity to boot.
March 14th, 2009 at 10:38 am
Hi Roger, I think there is another reality check associated with the wind and solar only option, and that is the combination of energy payback time (the time it takes for a PV panel or wind turbine to produce more energy that it took to make it in the first place) and rapid growth of an industry. This is especially a problem for Si-based PV (currently 95% of the market) where the payback time is about 3 years (at least that is what I am told by contacts at NREL). If you are looking at a short time scale (e.g. 2020), I think you need to look at how much net energy wind and solar are producing, because the energy needed to rapidly grow the industry will still be coming from fossil fuels. I wrote a simple spreadsheet for this at some point and the results were depressing. At high growth rates (e.g. 50% per year) the Si-based PV industry can actually consume more energy that it produces. Of course, eventually growth of the renewable industry lowers the carbon intensity of the overall energy supply, and the growth actually lowers carbon emissions. But I doubt if that happens by 2020.
Best, Carl
March 14th, 2009 at 11:34 am
#26 Carl Koval
New Jersey was subsidizing solar cell installation for a few years. I estimated (their calculator)the cost of replacing 0.75 of my average kilowatt usage. The cost over $40K and even with NJ putting up $27K it didn’t pay out for 10years.
Mike McHenry, NJ
March 14th, 2009 at 12:49 pm
I am confused about whether some of these numbers are projections or existing and by the number of EIA reports.. but looking at this.
From the EIA site linked in the post:
Hydro 2.5
Geot 0.35
Solar 0.08
Wind 0.32
Bio 3.6
Bio is 9 x (solar + wind), yet some states don’t even talk about bio in their renewable portfolio (or so I am told). What am I missing? Are we there already, so bio doesn’t need the attention/subsidies of solar and wind?
March 15th, 2009 at 5:42 pm
This post is confusing on the topic of primary energy use vs. usable energy (electrons on the grid).
The AEO forecast quads are all for primary energy — this is the raw energy in the fuel itself. (1 kg of solid coal has a certain amount of “primary energy”.) Given a OECD average coal power plant efficiency of 37%, the 22.75 quads of coal burned in 2007 generated only 8.4 quads of electricity. (This is before transmission line losses, etc, but those are the same for all technologies, except efficiency.) Natural gas plants are a bit more efficient, at 45%. The transportation sector uses primary energy directly (liquid fuel into your car), so that part is “100% efficient” compared with electricity. (The inefficiency is counted in a different place.) Since not all petroleum is used in cars, let’s assume it’s 95% efficient when counting “usable energy”. AEO Renewables are calculated directly from the energy in the lines, not from “primary energy” of sunlight falling on a given square meter, so they are effectively 100% efficient for this comparison. Nuclear is counted the same way (I think). The upshot of this is that instead of working with 102 quads of primary energy, we ought to be thinking about 72.6 quads of “used” energy in 2007. The most recent AEO numbers (downloaded from http://www.eia.doe.gov/oiaf/forecasting.html and then adjusted in Excel)) show this “used” number growing to 75.2 quads in 2020.
I’m a big efficiency fan, but let’s assume that number is un-changeable. Can we shuffle the proportion around between sources to add up to 75.2, while still cutting greenhouse gas emissions by 14% before 2007? Of course. Start by cutting coal in half. If the average coal plant has a lifetime of 30 years, this should be happening anyway over the next 15 or so years, as long as we don’t build new plants. 4.5 quads of used coal electricity comes from 12.2 quads of primary coal energy. Expand natural gas a bit: 13.1 quads of used natural gas power comes from 29.1 quads of primary energy (AEO forecasts 24 quads of NG). Leave petroleum where the AEO says, at 39 quads of primary energy. The AEO forecasts renewables growing from 6.3 to 9.4 quads. If this is accelerated to 11.5 quads, and nuclear stays where it is, we have 75.2 quads of “usable” energy on the grids/roads, using only 100.7 quads of primary energy, and emitting 86.3% of the carbon emitted in 2007.
Electric efficiency enters the computation the same way renewables do (and in fact better because it avoids the few% transmission line losses). So, if you don’t think we can grow renewables at a big boost over the AEO rate, just think about how to save 2.1 quads of end-user energy (per year) without hurting quality of life. Given that this is just 3% or so of total use, it’s not hard to imagine. (Refrigerators, for example, can easily be 20% more efficient today — look at all the Energy Star models available –and that’s not built into the AEO model.)
What happens if we set the “used” energy in 2020 equal to the “used” energy in 2007? If we just need a “useable” energy of 72.6 quads, we can even leave renewables where the AEO predicts them to be in 2020, and just do a straight swap of coal for natural gas and efficiency. Accelerated renewable R&D beyond the AEO forecast can push the natural gas number down, too.
It’s fun to play with numbers, but this post creates a false problem by ignoring the fact that the AEO numbers quoted are in _primary energy_ terms. I haven’t addressed any policy question here of how one would do this, but any option which results in enough increased renewables, efficiency, and natural gas at the expense of coal (relative to the AEO baseline) ought to work.
March 15th, 2009 at 7:14 pm
As Roger & others who post here always leave me in the dust, I have to struggle with non-familiar concepts to try to keep up. Presently, I’m hung up with the Mitigation Math as it’s not making environmental, economic or business sense to me.
Roger’s calcs suggest a 15% reduction of CO2 emissions by 2020 will result in 1.13 Gt less CO2 emitted. That 1.13 Gt equates to 0.14 ppm CO2 that has not been added to atmosphere in year 2020. If the climate has a 1.5 degree C sensitivity to a doubling of CO2 from a 380ppm base, the overall impact of a 15% reduction appears to be 0.00055 degree C.
Are my climate temperature impact calculations totally off the wall, or does everyone here just happen to know the impact is ludicrously low and basically unmeasurable? I gotta believe I made a major mistake in my arithmetic because I can’t imagine anyone would propose a 15% reduction resulting in such a tiny temperature “benefit” that I’m calculating.
(Note: if anyone can put together here a lucid explanation of the arithmetic regarding the global temperature impact of a 15% U.S. reduction of CO2 emissions by 2020, I’d be glad to post their explanation on my beginner’s site also, of course with full credit to author.) Thanks to any takers.