How the world can stabilize at 350 to 450 ppm: The full global warming solution

In this post I will lay out “the solution” to global warming.

I have argued that stabilizing atmospheric concentrations of carbon dioxide at 450 ppm or lower is not politically possible today, but that it is certainly achievable from an economic and technological perspective (see Part 1). I do, however, believe humanity will do it since the alternative is Hell and High Water.

It would require some 12-14 of Princeton’s “stabilization wedges” — strategies and/or technologies that over a period of a few decades each ultimately reduce projected global carbon emissions by one billion metric tons per year (see technical paper here, less technical one here).  These 12-14 wedges are my focus here.

This post is an update of my April 2008 analysis.  A 2008 report by the International Energy Agency came to almost exactly the same conclusion as I did, and has relatively similar wedges, so I view that report largely as a vindication of my overall analysis.

The reason that we need twice as many wedges as Princeton’s Pacala and Socolow have said we need was explained in Part 1. That my analysis is largely correct can be seen here: “IEA report, Part 2: Climate Progress has the 450-ppm solution about right.”

I agree with the IPCC’s detailed review of the technical literature, which concluded in 2007 that “The range of stabilization levels assessed can be achieved by deployment of a portfolio of technologies that are currently available and those that are expected to be commercialised in coming decades.” The technologies they say can beat 450 ppm are here. Technology Review, one of the nation’s leading technology magazines, also argued in a cover story two years ago, “It’s Not Too Late,” that “Catastrophic climate change is not inevitable. We possess the technologies that could forestall global warming.”

I also agree with McKinsey Global Institute’s 2008 Research in Review: Stabilizing at 450 ppm has a net cost near zero.

I do believe only “one” solution exists in this sense — We must deploy every conceivable energy-efficient and low carbon technology that we have today as fast as we can. Princeton’s Pacala and Socolow proposed that this could be done over 50 years, but that is almost certainly too slow.

We’re at about 30 billion tons of carbon dioxide emissions a year — and notwithstanding the global economic slowdown, probably poised to rise 2% per year (the exact future growth rate is quite hard to project because it depends so much on what China does and how quickly peak oil kicks in). We have to average below 18 billion tons (below 5 GtC) a year for the entire century if we’re going to stabilize at 450 ppm (see “Nature publishes my climate analysis and solution“). We need to peak around 2015 to 2020 at the latest, then drop at least 60% by 2050 to at most 15 billion tons (4 billion tons of carbon), and then go to near zero net carbon emissions by 2100.

That’s why a sober guy like IPCC head Rajendra Pachauri, said in November 2007: “If there’s no action before 2012, that’s too late. What we do in the next two to three years will determine our future. This is the defining moment.” Or as I told Technology Review, “The point is, whatever technology we’ve got now — that’s what we are stuck with to avoid catastrophic warming.”

If we could do the 12-14 wedges in four decades, we should be able to keep CO2 concentrations to under 450 ppm. If we could do them faster, concentrations could stay even lower. We’d probably need to do this by 2040 if not sooner to have a shot at getting back to 350 this century. [And yes, like Princeton, I agree we need to do some R&D now to ensure a steady flow of technologies to make the even deeper emissions reductions needed in the second half of the century.]

I do agree with Hansen et al that the basic strategy is to replace virtually all of coal as quickly as possible, which is why so many of the wedges focused on electricity — that, along with the need to electrify transportation as much as possible. I also agree that this will be harder and more expensive if conventional oil were not going to peak soon. But for better or worse, it is (see “Merrill: Non-OPEC production has likely peaked, oil output could fall by 30 million bpd by 2015” and “Normally staid International Energy Agency says oil will peak in 2020“).

Also, I tend to view the crucial next four decades in two phases. In phase 1, 2010 to 2030, the world finally gets serious about avoiding catastrophic global warming impacts (i.e. Hell and High Water). We increasingly embrace a serious price for carbon dioxide and a very aggressive technology deployment effort.

In phase 2, 2030 to 2050, after multiple climate Pearl Harbors and the inevitable collapse of the Ponzi scheme we call the global economy, the world gets truly desperate, and actions that are not plausible today — including widespread conservation — become commonplace (see here for a description of what that collapse might look like).

In the basic solution, I have thrown in a some extra wedges since I have no doubt that everybody will find something objectionable in at least 2 of them. But unlike the first time I ran this exercise, I have blogged on most of the solutions at length.

This is what the entire planet must achieve:

Here are additional wedges that require some major advances in applied research to be practical and scalable, but are considered plausible by serious analysts, especially post-2030:

  • 1 of geothermal plus other ocean-based renewables (i.e. tidal, wave, and/or ocean thermal)
  • 1 of coal with biomass cofiring plus carbon capture and storage — 400 GW of coal plus 200 GW biomass with CCS
  • 1/2 wedge of next generation nuclear power — 350 GW
  • 1/2 wedge of cellulosic biofuels for long-distance transport and what little aviation remains in 2050 — using 8% of the world’s cropland [or less land if yields significantly increase or algae-to-biofuels proves commercial at large scale].
  • 1 of soils and/or biochar– Apply improved agricultural practices to all existing croplands and/or “charcoal created by pyrolysis of biomass.” Both are controversial today, but may prove scalable strategies.

That should do the trick. And yes, the scale is staggering.

[Note: For those who prefer terawatts, 1000 GW=1 TW. I have adjusted the peak GW of the renewable wedges to take into account the lower capacity factor of solar and wind. The efficiency measures are assumed to have a capacity factor of about 60%.]

Note: The albedo effort requires a more aggressive effort than described in this post, one that California Energy Commissioner Art Rosenfeld detailed to me in a recent interview, which I will blog on later.

Why not more than 1 wedge of CCS? That one wedge represents a flow of CO2 into the ground equal to the current flow of oil out of the ground. It would require, by itself, re-creating the equivalent of the planet’s entire oil delivery infrastructure. I also think that CCS has practical issues that will limit its scale, not the least of which is that I doubt it will be among the cheaper solutions — as I explained here. But the possibility of doing CCS and biomass co-firing — resulting in negative-carbon electricity that actually pulls CO2 out of the air — makes this too important a strategy not to pursue aggressively.

Why not more than 1 total wedge of nuclear? Based on a post last year on the Keystone report, to do this by 2050 would require adding globally, an average of 17 plants each year, while building an average of 9 plants a year to replace those that will be retired, for a total of one nuclear plant every two weeks for four decades — plus 10 Yucca Mountains to store the waste. I also doubt it will be among the cheaper options. And the uranium supply and non-proliferation issues for even that scale of deployment are quite serious. See “An introduction to nuclear power.”

Note to all: Do I want to build all those nuclear plants. No. Do I think we could do it without all those nuclear plants. Definitely. Therefore, should I be quoted as saying we “must” build all those nuclear plants, as the Drudge Report has, or even that I propose building all those plants? No. Do I think we will have to swallow a bunch of nuclear plants as part of the grand bargain to make this all possible and that other countries will build most of these? I have no doubt. So it stays in “the solution” for now. [Note to self: Are you beginning to sound like Donald Rumsfeld? Yes.]

This is not to say the two wind power wedges (4000 GW peak total) would be easy — but the world did build over 27 GW last year, a 36% jump from 2007. We would need to average 100 GW/year through 2050. But I do think it is ecologically and economically possible, as I think all the other wedges in the top group are, too.

But none of the wedges is easy. That’s why getting to 450 ppm is not yet politically possible. Not even close.

Three more points: First, it bears repeating that the wedges are not analytically rigorous (as I explained in Part 1), but they are conceptually useful. We might need a couple more or a couple less.

Second, some people, like our friend Roger Pielke, Jr., mistakenly think we need a lot more wedges. I explain where he is wrong in Part 2.5: The fuzzy math of the stabilization wedges [warning: only for hard-core wonks].

Third, if you don’t like one of those wedges, you need to find a replacement strategy. Other possibilities can be found here, but I think the ones above are the most plausible by far, which tells you how dubious some of Princeton’s other wedges are [— I’m talking about you, would-be hydrogen wedges].

Could a bunch of breakthrough technologies substitute for some of the above wedges? That is far, far more implausible, as I will discuss next week (or see here).

Related Posts:

67 Responses to How the world can stabilize at 350 to 450 ppm: The full global warming solution

  1. Sounds about right, Joe! Nicely laid out.

    If you think you can compress the message into 2 minutes of video, you can submit it to an upcoming PBS special using user-generated video called “Planet Forward”.

    I made one on the renewable electron economy concept that I write about:

  2. Pangolin says:

    Where’s the disaster wedge? By which I mean how are we going to estimate the loss of carbon emissions due to large chunks of the human race finding an early death due to climate change related disruption.

    Politically, I don’t see Barack Obama funding a single wedge out of the US budget right now and Congress isn’t even showing as a blip on the horizon. Even the easiest, the most well established, the proven to pay the investment back, climate change mitigations aren’t being funded fully.

    The school across the street still has gas-pack HVAC units on each classroom and a black roof, and single pane windows. Not a solar panel in sight. There is no money anywhere to even get schools upgraded to best practices energy efficiency standards so the rest of us can go hang. Toss those efficiency wedges, no ground-loop thermal systems, toss most of your solar wedges, toss the plug-in hybrid wedge.

    Where the Fed and the Congress can find three trillion dollars to chase banks down the bad-money rabbit hole and solid engineering with proven returns can’t get funded we have a serious problem. A problem that will only be solved by large numbers of people experiencing the same kinds of world-view modification they received in Greensburg Kansas, New Orleans, and Galveston. (Is there still a Galveston? Yep, they have webcams!)

    Throw in a few disaster wedges to account for loss of human population while the majority of us go through the learning process.

  3. Robert T says:

    Just wanted to point out a typo in the title. It should read:

    “How the world can (and won’t) stabilize at 350 to 450 ppm: …”

    Sorry, but it just isn’t going to happen. Just for starters, how are you going to persuade the Chinese and Indians to stop building coal power stations, let alone shut down all the existing ones, when their per-capita footprint is so much lower than every developed country?

  4. Pangolin, Joe’s wedges are about planning to avoid disaster. You turn that idea on its head by including a “disaster wedge”.

    James Lovelock goes a lot further in the “disaster wedge” stakes with his “revenge of Gaia” hypothesis. He suggests, “billions of us will die and the few breeding pairs of people that survive will be in the Arctic where the climate remains tolerable” by the end of the 21st century:

    A more palatable idea than a “disaster wedge” is (planned) population control, but obviously that itself it hugely controversial and many people (and I suspect Joe included) avoid suggesting it as a strategy because of the controversy it inevitably leads to. It is much easier to suggest technological fixes rather than fundamental behavioural changes like controlling population.

  5. dougo says:

    To elaborate a little on the forest wedge. It’s not just tropical deforestation and afforestation. We also need to change forest practices outside the tropics, such as by adopting longer rotations and thinning instead of clearcutting.

    Here is a slide show clarifying many misconceptions about forests, logging, and carbon:
    (For full effect click “full” in the lower right.)

    Here is a more detailed foot-noted report on forests, carbon and climate change:

  6. Robert T says:

    Even 350 may not do the trick if you believe the more extreme predictions in this article:

  7. Dorothy says:

    Wait a minute, everyone. You’re all presuming that if we keep atmospheric CO2 level below 450 ppm, we’ll ‘save the planet.’ Can’t you see that this just doesn’t make sense?

    Let’s say that we’re at 400 ppm now; we’re almost there, anyway. What’s happening all around us? The Arctic sea ice is melting away, vast areas are burning up and drying up and the sea level is rising much faster than predicted. You think it’s OK to add another 50 ppm to this?

    And if we consider global temperature, the predicted 2C is too high as well. We may be stuck with this for a while, but we going to have to cool our earth down as fast as we can.

    If you look at all the graphs, you’ll see that at 325 ppm, the Polar Ice Cap hadn’t started to melt. This was early in the 1950’s. It was a little cooler then, but our planet was a happier place for living things. The world’s oceans were cooler and less acid; sea life was abundant.

    That’s where we need to be. Once we know this and force world leaders to recognize this, we’ll find a way to get there and stay there. We have amazing brains, the inate ability to solve this problem. We don’t yet know how smart we really are. I have great hope that we’ll learn in time.

  8. paulm says:

    Good shot Joe.

    We must also throw a wedge or 2 (???) in, to account for the reduce uptake of CO2 due to the warming effect on the sinks.

    Now lets budget for each wedge! Also we have to add adaptation in the mix for the 2-3+dC were definitely in for.

    I don’t see Nuclear happening. There is going to be too much expertise and resources taken up in clear up coastal facilities to even begin on new plants. Oil prices are going to be high, so than needs to be accounted for.

    How do we get from 400ppm back down to 300ppm. Dorothy is right on …we have to get back down to 300ppm pretty soon. The next few years will give us and idea how bad a 1dC change is going to be.

    Will this work? I doubt it. But this is the only way forward to give us any hope.

    All eyes on the permafrost & methane levels now. Also on the social unrest which has started to follow the CO2 level now.

  9. James Mapes says:

    With regards to the 450-by-2050 question, 450 is a number because – as this blog points out – it’s on the edge of possible. Also, despite the climate disasters occurring at the margins (and the Swiss and Italians redrawing their borders because of glacier melt!) a lot of climatologists believe that 450ppm will be enough to avoid fast positive feedback cycles that could push us further. Then, once we’re stabilized, we can turn our attention to turning carbon-negative and return the level to 280ppm.

    Of course, a fair number of articles that this blog has posted lately question whether 450 is going to be low enough. Still, given that list, it seems unlikely that we can even reach any lower…

    Personally, I would put my bets on a larger conservation-related wedge. Right now, the United States and Europe are responsible for a huge portion of carbon output, and just watching three hours of cable television over the last week has shown me that a good third of the ads are climate change-related, usually on the topic of energy. A huge movement is starting here – and if we play our cards right, we can spread that movement (and its wisdom) to the rest of the world before they start repeating our mistakes.

    It may be a bit optimistic, but I think large-scale conservation efforts will start before 2030. A huge part of that is going to be recasting the environmental debate, though.


  10. Paddy says:

    HI Joe-where does greater switching from cars/trucks to public transport, rail etc come in? Is it in your efficiency wedge or don’t you think it will improve carbon efficiency over all transport?

  11. paulm says:

    This is not paint drying….

    Extreme Ice (only for US viewers at moment) wgbh/ nova/ extremeice/ program.html

    Rising temperatures, driven by fossil-fuel burning, are pushing Greenland towards a major meltdown. The last time the island lost a significant portion of its ice, it happened over thousands of years, glacier expert Jim White suspects. But this time, it could happen much faster, he says.

  12. Jim Bullis says:


    So you think working with technologies we now have would be a good way to get started? How about some that would not cost much either.

    Unfortunately solar is not there for my level of spending. Even insulation has its limits, though for new construction it works well.

    The “smart grid” sounds fairly smart, but the promise of smart has a real problem when it confronts the Public Utility Commissions and power companies.

    Previously cogeneration has been mentioned here. It is well known in the world of electric power generation, it seems to be easily forgotten in these discussions.

    However, simply by using the heat that is otherwise thrown away in central power plants, two to three times as much electric energy can be produced from a unit of heat energy. The microgrid concept (not the “smart grid” that seems to be getting people excited) makes it conceivable that the heat can be used.

    With central power plants located far from population centers the only thing to do with the heat is send it up the stack or warm up a river; “smart” can not fix this.

    In a small grouping, there might be a way to use the heat. The “microgrid” concept seems interesting.

    Hey wait a minute! If you put generators in or close to houses that actually can use heat, the whole thing gets double or triple the efficiency. (Actually there is a product that does this; I think it is from Sony. There we lose it again!) Anyway, then tie these into a small grid that also uses stuff like solar. Now we get very efficient power on sunny days and still quite efficient power at night and on cloudy days. So now the only big ticket items are the power units that go in the houses and, of course, the solar panels.

    Hey wait a minute! If we get hybrid cars, they already contain most of the machinery that is in the power units that we were going to have to buy for some serious money. But we have the cars anyway, and much of the time they are parked near their owner’s house.

    There is a little problem; well, it is a big problem because cars are generally way too overpowered to work well in this way. It is hard to get great big engines to run very well at low power outputs so typically there is too much heat for the household. And the efficiency does not get good unless all the heat is effectively used; by that I mean that it displaces the use of fuel that would otherwise have to be burned to give the household the heat it needs.

    Hey, maybe we could learn to live with cars that can get along on much smaller engines. Actually we can if we want. The not so sophisticated secret is to significantly cut the drag, especially the aerodynamic drag. (We certainly are not going to get ourselves to drive slow, so there is a very big payoff here.) The Aptera at might be a way to do this. Certainly the Tata Nano would fit, but that is a little too little for the USA. Another possibility is at (You know I represent Miastrada Company.)

    So why not push hard for a big leap in efficiency of cars? Of course, in comparison the Joe Romm Prius will look like a Yukon.

  13. crf says:

    Why is solar baseload the number that it is (3): couldn’t it go higher?

    [JR: It could, but I have tried to balance things out with as much plausibility as possible.]

  14. Pangolin says:

    With all due respect to the intelligence, dedication and hard work of the people working towards solutions to the problem of climate change you/we are individuals. At best we’re a very small group committed to understanding the details of a very large problem with a tiny resource base.

    The human race, in large groups, is a total moron. I’m insulting morons here as most of them are gentle, tractable people. The body politic of the United States seems to function on the level of a two year old producing political decisions with the subtlety of said toddler screaming “gimme cookie.” The UN might as well be a daycare for all the actual work achieved by representative ambassadors.

    My personal assumption is that we aren’t going to get a single wedge worth of action funded during the Obama administration; not one. Any pollyannas out there need only look at Obama’s dismissal of single payer health care in the face of near collapse of the health care system in the US and the functional example of Canada’s system. We can’t make the right decision even when it’s staring us in the face.

    Disaster needs to be a wedge. Loss of carrying capacity and resulting famine needs to be a wedge. We should probably assume that war on the population killing scale of WWII is a wedge also. Assuming the world is going to spin in place and head 180 degrees from the current course without losing passengers just isn’t realistic.

    This lifeboat is going to lose passengers. Say goodbye to Florida, Venice, Holland and Bangladesh; they’re gone. No reason to stop bailing; it’s a big boat.

  15. Joe, pardon my contrarianism: While your wedges are a hopeful engineering proposal that is possible, they are not likely without colossal foundational change.

    We might consider the opposite of wedges – call them thorns. (like a wedge in the opposite direction) Thorns prevent wedges – resistence to change. They will make life difficult for us like walking through a patch of thorns.

    The biggest brier patch is the momentum of our entrenched carbon based economy – call it 10 thorns; then human denialism, avoidance and deliberate ignorance – 2 thorns. I am pretty sure that ideological delusion and political resistance will give us 4 thorns. Then the challenge of global enforcement difficulties (will it take jets to bomb coal plants?) – 4 thorns. Finally, the climate wars, refugees and peacekeeping during chaotic times will be a huge energy drain – 3 thorns.

    Although your wedges are well defined, most do not exist yet and need to be fully deployed. But the thorns are already fully deployed and mean.

    Wedges are a good idea – probably the best – a worthy good goal, and we should work in that direction, but we must ruthlessly evaluate the sharp resistance that will be hard to clear out.

    Poetic justice requires roses must appear somewhere.

  16. jorleh says:

    Very sorry to say Joe: when you look around, there are billions of people who don`t know anything of our coming climate catastrophe. And some more billions to say: there is no problem with our climate warming a bit. And some hundred millions knowing something of the climate change but believing dead sure it is alarmism to take notice of it.

    I agree with you in every wedge. Of course we must try to tell the solutions. But there are of us only a few millions taking to some serious action. We are lost.

  17. paulm says:

    Climate Catastrophe by a 1000 cuts….extreme rain event due probably to GW.

    Indonesia dam burst kills dozens
    …He said there had been heavy wind and rain overnight with many trees uprooted.

  18. Mark Shapiro says:

    Good work, Joe (and commenters). Yes, we sure like to talk solutions here.

    The wedge concept is very useful, since it organizes solutions quickly and simply. I would also love to see discussion of systematic decarbonization: designing zero carbon buildings and whole cities in ways that make them both more functional and esthetic, using architecture, design, planning (and other professions?) to combine efficiency and renewables. This isn’t the right blog for such speculative stuff; William McDonough, RMI, and others tackle this somewhat.

    Regarding Pangolin’s concept of disaster wedges, we can only work to prove him wrong. The people of Florida, Holland, and Venice can all move to higher ground. In Bangladesh, there is no higher ground.

  19. Bob Wallace says:

    “… when you look around, there are billions of people who don`t know anything of our coming climate catastrophe….”

    That could be a bit of overstatement.

    I’m currently in Bangkok, just spent some weeks in Cambodia, Vietnam, and Laos.

    People in this part of the world certainly are familiar with global warming. It’s frequently in the media. Politicians are discussing global climate change and what to do on a regular basis.

    Additionally I’ve been watching the Russian TV network (it’s no worse than Fox or Bloomburg – my US based choices). The topic is old news, current news is about solutions.

  20. Indeed these wedges are a usefull tool to effectivly assess the various technologies to cut our CO2 emissions.
    But, with all due respect, I think all this is measured from the producer point of view, and that the consumer, or citizen, point of view is missing.
    The technologies and the industry will not bring the solution alone. We, individual, must understand that we also have to change our way of living to meet the ethical target of the same ges quota per individual.
    This target, corresponding to halve the earth ges emission in 2000 by 2050 is something like 700 carbon kilo per individual (carbon equivalent for CO2 and CH4 and N2O, …).
    My point is a simple complement of yours: OK for the technologies investments, there are urgently needed, but we individual have also to cut our carbon emissions.
    This is why a carbon tax, with dividend, is so interesting; it gives the financial drive to our individual choices, and also to the business choices.
    This is why a cap and trade is a weak solution, particularly because it doesn’t involve our individual commitment (reade Stoft on this).
    Thank you for reading up to this.
    If you want to read more, in french all your comments will be very valuable:

  21. When i read the title, “How the world can (and will) stabilize at 350 to 450 ppm,” i tend to think as much of the social/political/legal challenges as the engineering challenges. Copenhagen as much as wedges.

    Just published two articles by Peter Singer and Dale Jamieson on the new global citizenship.

  22. A Siegel says:


    This is extremely good.

    Some thoughts (echoing some above):

    1. Rather than CCS, why not consider potential impact of “CCR”: Carbon Capture and Reutilization. What could a pure C stream (cracking the CO2) do in support a carbon fiber / carbon material industrial stream? How much could be 100s/1000s of years “sequestered” by becoming a core material for all sorts of industrial and building uses?

    2. Yes, advances (lots) required, but perhaps your algae and other ‘alternative’ biomass options (whether for dry or liquid fuel) is understated.

    3. Waste to Energy? Whether the McDonald’s fries biodiesel or methane digesters or going in and ‘mining’ dumps.

    4. Electrification of rail.

    5. Inter-Modal Transit System (electrified as much as possible) with bikes/NEVs for local, bus/light rail, local rail, interurban/long-distance (moderate speed, minimum, to start: 100 mph cargo and vegetables are 30 hours from CA to DC).

    6. Additional renewable energy options. Just in “water”, advanced hydro, in-stream, ocean power (wave, tidal, OTEC), …

    7. … others …

    4 & 5, combined, is probably wedge+ level. 2 has potential for wedge+. 6 might be in wedge+ territory. Etc …

    And, there have been some good comments above … the questioning of whether one wedge of conservation is enough, for example.

    The challenge of whether (how) to include population (and family planning) in the discussion.

  23. Jon B. says:

    Warning, this post edits all opposing viewpoints.

    [JR: As everyone can see who reads the comments, that is not true. But I have a long-standing policy of not publishing long-debunked denier talking points. If you want to spread misinformation, go elsewhere.]

  24. hapa says:

    pangolin, sheesh, leave something for the secret memos.

  25. darth says:

    How about a partial wedge for reduced airline travel. Businesses need to reduce the ridiculous amount of executive travel they now do. With our advanced telecomms, why do people still need to fly across continents to have meetings? It is absurd in the extreme. Business travel still seems to be a ‘perk’ of being at a certain level of mangement – that needs to stop. Or we create enough bio-jet-A fuel to run our airlines. hmm.

  26. ecostew says:

    We should alter our diets, eat less, walk more, live in smaller spaces, buy less stuff, etc. The per capita carbon footprint in the US must be reduced by a factor of five.

  27. Mike Keller says:

    Might want to take a look at
    Offers an unexpected and more practical solution.

  28. Joe,
    Thank you for your denier policy. It is a great luxury to get rid of these lengthy and irrelevant claims when reading the comment section.

  29. paulm says:

    ecostew, the US foot print will be drastically reduce whether voluntarily or not in the near future.

    Meat production and consumption is a big CO2 emissions component (18%?).
    There part a wedge in this somewhere.

  30. Sasparilla says:

    Pangolin, regarding the disaster wedge….to be perfectly brutal, we’ve got about 6.5 billion people right now – there’s about 2 billion more coming in the next 20 years (basically in the pipeline) – i.e. it’ll be a while before we’re even back down to todays population. It will be a while before we can count on a disaster wedge to really effect CO2 output (much of the early losses will be in places that aren’t and won’t be big CO2 emitters – much of the 3rd world that will be really hit early on use biomass for daily energy, i.e. don’t affect CO2 levels appreciably).

    Even at 450ppm the world won’t have the farmland area we have today to supply the food (i.e. there will be alot less of us by the end of the century more than likely), but the impact will be hitting the people who don’t make alot of CO2 emissions for the most part (which is most of the world’s population). as Joe has laid out, solutions count on stuff we can do, not hoping a large part of the 2nd or 1st world population dies – cause we don’t know if/when that will happen.

  31. Pangolin says:

    Sasparilla- The example of the population of the Former Soviet Union declining in response to economic disruption shows that population increases are not written in stone any more than housing price rises are. There were also once endless forests of virgin redwoods and endless schools of Atlantic cod.

    Nobody, and certainly not my self is “hoping” that there will be a die-off. I’m personally working to promote a miraculous and nearly instant transition to biochar and permaculture agriculture. Humans have lived in balance with nature in the past. The area we now call the Amazon was once home to a permaculture of several million people that rapidly transitioned to ‘virgin rainforest’ when they died off.

    Working for change should not preclude preparing for a continuation of the status quo. Every good roofer carries tarps on his truck and ties his ladder to the roof. Stuff happens; prepare for it.

  32. paulm says:

    I cant see the world pop increasing by 2billion in the future.

    It just isn’t going to happen, there wont be the resources due to peak oil and CC and there will be huge social unrest.

  33. Jarad Holmes says:

    Has anyone seen the latest daily images of the Arctic and Antarctic for the past two years?

    Holy Cow!

  34. J4zonian says:

    Thank you for this post and your denier-access-denial policy. It is good to have places to sharpen our fangs and come back to unreality by talking to them, but we also need this community so we can talk about solutions and forge ahead with the ones we can accomplish without convincing the dinosaurs. Low-hanging fruit can feed a lot of people.

    So how about changes in food and ag–doesn’t that count as a wedge? a substantial percent of us going substantially vegetarian, some going vegan, and a move back to the agriculture of the late 19th, early 20th centuries–local organic, plant/animal-integrated farms and homesteads(milk, egg, fiber and work animals where ecologically appropriate)…

    Personally, I think it would be a wedge and a half to outlaw useless fitness work–requiring all gyms to either close or hook the machines up to generators, and be available only to pedestrians and cyclists. But maybe that’s just me. Doncha think? A civic duty to spend every workday lunch pedaling to offset one’s use of copy machine, coffee machine and computer? Or integrated work station pedal generators…

  35. Paul Ray says:

    Thank you so much for this beautiful work. I too thought Socolow’s wedges made good rhetorical sense, but lacked technical completeness and convincingness.

    I’ve been posting links to your key posts on website which is the website of State of the World Forum, 2009 conference in Washington, DC. I hope this way of doing it meets your approval.

    Please let me know how we can contact you and ask you to participate. You’ll like our lineup of other speakers.

    Warmest regards
    Paul H. Ray, Ph.D.
    Director of Research

  36. JeffFa says:


    Great post.

    When you say we need to average below 18 billion tons per year (5 GtC) for the entire 21st century, what assumptions are you making about the arctic methane releases and its potential positive feedback loop? Is this baked in to your timeline that allows us to get to 450 ppm within four decades assuming the implementation of 12-14 wedges? How much room do you think we have before we trigger a runaway effect?

  37. Roger says:

    Thanks, Joe, and everyone. This site is a good mental workout.

    I wish we could hook our brains up to produce power, or better answers!

    Anyway, keep the thoughts flowing—we need more thought, and action…

  38. paulm says:

    Jarad Holmes, yeah and thats just the extent. The volume is at record lows too.

  39. A Gallup poll published March 25, 2009, found that only 34% of Americans are worried “a great deal” about global climate change, and another 26% are worried “a fair amount”, while 40% are worried “only a little or not at all.” The biggest worry was pollution of drinking water (59% worried a great deal).

    My point is that the political impetus is just not there. Maybe it’s a sign that Americans have surrendered to the inevitable, and are hoping that the bad news will turn out to be wrong.

    [JR: I don’t agree with that interpretation. Other than Gore with AIT and the IPCC back in 2007, there has been very little discussion of global warming in the political realm (because Obama and McCain largely agreed on it), and the media generally ignores issues that leading politicians don’t talk about and that they think they have covered. And, of course, the grim news of the global economic recession has crowded out everything else. You’d hardly know we are fighting two wars if Obama work actively talking about Afghanistan.]

  40. Bob Wallace says:

    I’d start with the 60% of Americans who are worried “a fair amount” or more.

    That’s a majority.

    And they are willing to spend public money to work on the problem.

    Let us spend a few more months getting through the worst of this recession and I think you’ll see public concern about climate change rise quickly. Just recognize that we’ve got a very large (but short term) problem striking us right now.

  41. alan leener says:

    I have technology available founded by Dr Vernon Trigger that will reduce green gas caused by the burning of coal. I have yet to have one person in Govt. even have the courtesty to answer my email. If I could have a reply my partners and myself would love to discuss our technology. I am taking it to China to see what I can do there. It will honestly do wonders for our planet.
    Alan Leener

  42. James Newberry says:

    Photosynthetic efficiency average 0.3% sun to chemical (carbohydrates).
    Coal (deoxygenated carbohydrate) combustion to electric conversion average approx. 30%. Sustainable energy efficiency of sun to electric via coal: 0.3% x 30% = 0.09% Get the picture?

    The bioshere is being massively poisoned by carbonic acid (CO2 + H2O) to the extent of some thirty billion tons of CO2 per year, and the patient has developed a fever. Major biologic systems are beginning to crash. It is now a fight for life, or further disease and death of biodiversity is assured. Choose life, and prepare for a massive transformation one way or another.

  43. Tom O'Neill says:

    One of the biggest, fastest things that could be done now to attack global warming is never mentioned, totally,in the press: namely, putting PV solar on every frickin’ rooftop of every type in the country- using the German program as as a model, or bettering their program. The kicker now is: here comes the EV and plug-in hybrid car tidal wave. Even the low range GM Volt will go 40 miles on battery power alone- this exceeds the range of 75% of the people commuting in the U.S. The price of solar, if ramped up in huge volume, and with cheaper tech. like Nanosolar as well-and with both state and federal govt. incentives- would drop thru the floor. You’d be looking at system payback time of months, not years. With systems lasting at least 25 years before starting to degrade, you’d be looking at like 24 years of FREE building power AND car power, for most people, most of the time. The solar use in powering your car would further speed up system payoff time. They say that the entire U.S. could be solar powered from a patch of southwest desert land about 100 x 100 miles. There is many (many) times this area in all the rooftops in the U.S. -and with PV rooftop solar , there would be no, or very little, power loss over transmission lines (power is made right where it’s used, or very close by)-which can be up to 7% loss-which, added up nationally, is a huge amount of power. PV rooftop solar is fast & easy to install, comes in many varied forms, and is so “highly scalable”: now. This should be a MAJOR national priority. No doubt it isn’t due to the power co./fossil fuel lobby- since it also would allow eliminating the power company middleman, for most power-it would be “power to the people”- directly- and, over time, it would put a huge amount of cash back into people’s pockets every week -“forever”- thru savings in car & building power- especially once initial PV system cost paid off-which, ultimately, like I said, would be very quick.

  44. TD says:


    Speaking of solutions, I’d love to hear your thoughts on Rep. McDermott’s new climate bill (HR 1683). At first glance it seems to be a tax/cap hybrid that avoids the pitfalls of each, with no offsets or trading. Whether I’m missing something or not, hopefully you will blog about this soon. If it’s the real deal, it means a big step toward making the solutions discussion more than theoretical.

  45. CV says:

    What’s the potential price tag of implementing all these wedges. In cash, manhours, skilled labor and resources?

    That would seem to be an important part of the discussion.

  46. Roy says:

    You’re no doubt aware of

    If black carbon is truly responsible for half of observed arctic warming then reducing BC seems a very attractive wedge. Especially since the results are virtually immediate diminution of the related warming. It’s just old fashioned “pollution”!

    My 2 cents.

    [JR: I will get around to blogging on this. Slashing BC is a great idea, but will take a lot of work.]

  47. While reading the NREL report on CSP, I came across a link about an alternative heat storage system for solar thermal plants. It uses alumina pebbles with CO2 as heat transfer medium. The claim is that it’s a big improvement over molten salt heat storage because plants can operate at higher temperatures and therefore be much more efficient.

    The inventor says it can be fitted to existing plants. He describes one scenario where a power tower plant is used to increase the temperature of the transfer medium of a larger solar trough plant, making the overall system more efficient.
    He says its built from existing proven technologies arraanged in a new way.

    Any thoughts on this?

  48. “We must deploy every conceivable energy-efficient and low carbon technology that we have today as fast as we can.”

    I question the intrinsic sensibility of that statement — which evidently means that I cut a “logic” class in graduate school. Here is the basis of my conundrum, based on a simplified, made up example:

    Let’s say that we have TWO “energy-efficient and low carbon technologies.”

    #1 costs $100M/MW to build, is 30% reliable, and has ten serious environmental side affects.

    #2 costs $50M/MW to build, is 95% reliable, and has five serious environmental side affects.

    Your contention appears to be that we should treat these as equals, and get as many #1’s as possible. The fact is that the more time and money spent on #1’s, the less time and money would be spent on #2’s. That makes sense?

    It seems to me that (in my example) we should focus on getting the maxim quantity of #2’s employed, and forget the #1’s.

    In other words, cost, reliability and environmental effects should dictate where we focus our efforts.

    This seems in contrast to your apparent message that seems to be saying: do something everywhere no matter what the cost, reliability or environmental effects.

  49. Fran Barlow says:

    Love the sentiment Joe — you’re one of the good guys but …

    1. CC&S is a dead dog. It can’t work in any timeframe of use to humanity and compared with any number of Yucca Mountains, its storage implications are horrendous. It would make more sense to focus on some of the new technologies aimed at using the flue gas to make portland cement. That might work and given all the concrete we are going to need, is borderline feasible

    2. We absolutely positively have to do something serious about reducing total demand for resources. There’s no escaping that. Sustainable cities in which far fewer people need personal transport is key, as is making much better use of the biomass waste of cities (energy for example)

    3. The real carbon capture project is in stuff like algae — not to reburn as fuel but to sequester carbon. Large areas of non-arable land could be used to contrive large algae farms. When the stuff dries, bury it at the base of disused mines under some stable medium. If we’re doing desal that copuld be salt of course. Deep ocean storage would be another place.

    4. Pumped storage is the key to unlocking the full power of intermittent sources of energy such as wind, tidal, wave, solar thermal. These facilities can both serve the conventional grid, making for much better load shaping and reducing the need for spinning reserve and make highly volatile wind sites viable.

    Best regards


  50. Ray says:

    Your view point is not to be challenged; right? It is no wonder that so many skeptics are “cropping up all over”. It is obvious, just as the NY Time is known for, that the real truth cannot be told through the “smoke screen” you are generating. Incidentally, I am a Professional Engineer, Board certified by The American Academy of Environmental Engineer. As a professional, all subjects are open for debate. It appears, in your mind, this one is not.

  51. Neil Howes says:

    You didn’t mention hydro power, I think you said you were planning an article, this post may help

    Basically expanding hydro has great potential but should use a continental North American approach.

  52. Steve Lusky says:

    Another substantial benefit would be for “intelligent transportation systems” that focus on synchronization for energy efficiency. The prominent meter in the windshield would be the MPG, since speed would be managed automatically. We have the capacity for wireless systems to bridge among vehicles and traffic control devices.

    If you and your vehicle know that a traffic light is to turn red in 30 seconds and you are 31 seconds away, your car would tell you and start regenerative breaking (or simply coast) so you would arrive at the light after the red when the light is turning green without the need for a full stop nor the energy to accellerate from a full stop. Convert stop signs to round-abouts where your cars automatically stop only if another vehicle (or pedestrian/cyclist) is detected.

    On freeways, cars would automatically match speeds to avoid the accordian-like stop and start waves during heavy traffic, and enabling higher traffic densities that reduce the need for extra lanes (and the high CO2 of concrete plants). Turn on your signal indicator and cars in the next lane will make a gap to let you in.

    The difficulty is not so much technical as attitude. Car companies still market speed as the prime motivator to sell cars. Drivers prefer “performance”, high gas costs and traffic jams.

  53. Mark says:

    Nobody has answered Dorothy’s sound observation that we have to go significantly lower than where we are now – perhaps back to 1950s levels (and perhaps lower) because its all falling apart already.

  54. MrPete says:

    You might as well drop the wind power wedge and allocate it elsewhere. Wind is proving to be environmentally disastrous. Has terrible consequences for avian life, etc. As that realization begins to sink in among communities of influence, the realistic prospects for major wind power deployment are rapidly heading south.

    [JR: Not. China is up to a 100,000 MW commitment by 2020. And we’ll be close to that.]

  55. Nichol says:

    Was there a rule forbidding a dirty wedge, doing some geo-engeneering, just to postpone disaster somewhat? Something like a sulfurious addition to jetfuel of airplanes. Much better than the pure disaster wedge of collapse.

  56. John Pearson says:

    “It is much easier to suggest technological fixes rather than fundamental behavioural changes like controlling population.”

    this is true. however the implementation of those changes will prove to be a great deal harder than simply having less children.

  57. bb says:

    The earth is not over populated by humans. The entire human population of the earth can fit in the continent of Australia. I’ll prove it. Every man, woman, and child can have 1/4 acre of land. A 1/4 acre of land can fit a 2-story 2-bedroom townhouse with solar power and a self-sustaining garden. I know it is possible, because I live on 1/4 with a 2-story 2-bedroom townhouse and a garden, BUT no solar power yet. Now, here is the numbers:

    1 sq mile = 640 acres; Australia is approx. 3 million sq miles
    640 x 3 million = 1.95 billion
    approx. 7 billion people who each get 1/4 acre
    1/4 x 7 billion = 1.75 billion

    So, as you can see, Australian holds approx. 1.95 billion acres which is more than 1.75 billion acres needed to give 1/4 acre to every man, woman, and child of an approx 7 billion human population. Each 1/4 acre can fit a 2-story 2-bedroom solar powered townhouse with a 1 person self-sustaining garden. Now, this will leave the continents of Europe, Asia, Africa, Antarctica, South America, and North America NOT inhabited by any human.

    The problem that we are facing is not over population, but MIS-management of what we have. This article’s wedge proposal is a very good step in a management solution. I agree with the wedge proposal, but not with a Cap and Trade tax (which has been proven a failure as a solution in many countries) to be implemented in the U.S.

  58. Glenn Tamblyn says:


    Perhaps deserving of a separate wedge is energy storage. Not any particular type but all possibilities. Because one of the biggest limitations for solar and wind is energy storage. Without that, the amount of energy that these sources can supply to a grid is very limited without breaking the grid. Even with smarter grids and HVDC and other developments. Also storage is central to transport energy.

    And applying energy storage technology effectively needs to be done at the right scale – batteries in every home for your solar panels vs huge grid connected battery farms that provide load balancing for whole regions; pumped storage as giant hydro projects vs tanks in your roof and cellar. Getting the mix of scales right for each type of technology is important to getting the optimum benefit from each technology and maximising the efficiency of the technology’s use of resources – just how much lead will we need for all those billions of old fashioned batteries; how much concrete for all the pumped storage facilities, etc.

    Energy storage is potentially a critical enabler for other technologies, to some degree taking the base load demand constraint off the energy generation technologies back and seeing it as a storage problem instead. This can give us greater flexibility in how and on what scale we deploy the products of the other wedges.

  59. Watch It! This is a double edge sword!!
    “Scientists analyzed data from a major expedition to retrieve deep marine sediments beneath the Arctic to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” This 2006 study, published in Nature (subs. req’d), found Artic temperatures almost beyond imagination–above 23°C (74°F)–temperatures more than 18°F warmer than current climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.”

    Yes, Houston, and the world, we’ve got a problem! A BIG one!
    The other half of the analysis is to determine how did the CO2 disappear?

    It is my understanding that CO2 is an stable molecule and would last indefinitely, am I wrong? Does CO2 disappear in a million years?
    Is that process known? Can it be duplicated and enhanced? Provided, of course, that witchcraft had nothing to do with it, or a meteor blew the atmosphere away, or some other crazy and incredible idea.
    How about the Super Nova that sent Gamma rays, a long time ago, and blew our air molecules apart? Did I read that somewhere, more importantly, did YOU?

  60. James Moore says:

    “The earth is not over populated by humans.”

    Ever driven on a busy motorway? Look to the world around you for evidence and then apply logic. Australia is also 100% arable land I suppose is it?

    The world has a surface area of 154,000,000 sq km and only 12% of it is arable land. One equation states that humans require 4000 sq m of arable land for food production and 83,333 sq m for living space. Put that together with our population of around 7 billion and the planet can only sustain in complete abundance 529,000,000 human beings. But then again you didnt need an equation, you just have to look around you for evidence; high house prices anyone?

    The planet is therefore most definately overpopulated. The optimum population is 529 million. Thats if you want everyone to have decent living conditions, eradicate poverty and for everyone to live in total abundance of food and energy.

    In addition to taking care of our world I would rather live in one where most of it has been returned to a natural state and we are its guardians, not torturers and desecrators. I also do not want my grandchildren to be forced to live in high rise flats like rats in a cage or any kind of flat for that matter. Every family deserves a decently sized family home and garden in order to bring their children up in appreciation of nature and being very close to nature, our world. It is there to be appreciated, not utterly exploited until the last gram of resource has been dug or drilled up, dont you agree?

  61. Thanks for posting this information and analysis

  62. MarkR says:

    The only solution to global warming is for seven billion human beings to disappear rapidly. This will likely happen soon. Oddly, no one is focusing on this aspect of the problem because it seems so inhumane to do so. Also, no one looks at the explosive human population curve as graphed and draws the connection between it and the increase in oil extraction; the two curves match. If peak oil is hit soon, and there are no immediate alternatives, that population J-curve spike may be driven downward in an avalanche of snowballing feedbacks regardless of climate change. This will end all debate about what to do about climate change, as there will be few humans left alive to act on it one way or another. I do not yet know what will trigger such a collapse in population but it happens to all other animal species which overtake their environment, and there is no argument that can be made that it won’t happen to us as well. I can guess that it would be a number of factors: shortfall in oil output leading to shortages of nitrogen fertilizer, electrical grid failure because of interrupted supply, leading to social chaos and disease from lack of water hygiene, sudden massive drought inflamed by climate change which leads to large-scale agricultural failure of staple crops. I believe that it will happen sooner than anyone can guess, at a larger scale than anyone would imagine, and will comes as a complete surprise to the human race, as if we’d suddenly realized that we’ve already stepped off of the precipice but haven’t quite yet fallen.

  63. Jenli says:

    Naive and out of reality is this proposal.

    The MEF leaders set the +2°C goal as a best guess. As a consequence, the corresponding concentration target is roughly 450 ppm CO2-equivalent and possibly lower.

    The present level of GHG (Green House Gas) concentration is 430 ppm CO2-eq (390 ppm CO2 only), well above the 380-390 ppm level necessary to make a temperature increase above 2°C unlikely.

    430 ppm is also very close to 450 ppm, a threshold value that will be reached in a few years, whatever world leaders decided in L’Aquila and will decide in the coming years.

    In the absence of technologies that can absorb large fractions of the stock – not just the flow – of GHG emissions, the 2°C target could be achieved with a median likelihood only if emissions are cut to virtually zero worldwide, starting from 2012 onward. This is clearly unrealistic.

    Interestingly, even the emission reduction path proposed at L’Aquila is not fully consistent with the 2°C target. If we assume that emissions will halve by 2050, declining at a constant pace from 2010, concentrations of CO2 in the atmosphere will be 40 ppm higher in 2050. … This implies that all GHG concentrations will reach 470 ppm in 2050, assuming that emissions of non-CO2 gases are heroically cut to zero from 2010 onwards.

    The emissions path envisaged by MEF leaders is thus more in line with a 525-550 ppm target by the end of the century, which corresponds to a global warming of about a +2.5C° / +3.0C°.

    The +2°C target is therefore an unlikely option without technologies that yield large amounts of negative emissions, a possibility that now appears highly speculative. In addition, in the case of delays in adopting mitigation policies, limited participation in a global climate agreement, or both, even the more modest 525-550ppm CO2-eq target would not be attainable. In terms of temperature rise, this means that a 2.5-3°C target is much more likely than 2°C.

    An immediate consequence of this conclusion is that an optimally designed climate policy should entail a detailed and credible plan for both mitigation, and adaptation. A realistic target – technologically feasible, politically achievable, and economically inexpensive – would be to stabilise concentrations of all GHGs at about 600 ppm by the end of the century. This would anyway represent a remarkable commitment, if we consider that without controls GHG emissions can easily increase to 800-900 ppm CO2-equivalent by 2100. At the same time, long-term commitments to adaptation plans, particularly in the more vulnerable developing countries’ regions, should be adopted, the related funding should be made available, and their implementation linked to development programs in non-OECD regions.

  64. I am very impressed with the very high quality of all the comments. This, accidentally, includes mine (#61) which I read, w/o recognition.
    To answer my own question: Yes, it seems there was a Super Nova close enough to do split the CO2 and whatever, in the air. No, it cannot be duplicated, stars are hard to move for distances much over a light-year and timing is important, the explosion might not be predictable.
    This, however, blows up the idea of replicating THAT process.
    Did read “Robert T. (Mar 25, 2009)” comment “how are you going to persuade the Chinese and Indians to stop building Coal Power Stations?” He brings the confusing real world into the picture with a simple question with no known answer. Perhaps, in Mexico City these nations will let us know what is the answer.
    But, while on the subject of the “confusing real world”, the assumption that Nuclear Power is part of the solution seems, at least, unrealistic. It is my opinion Congress will never approve the Yucca Mt. Nuclear Waste Site, ever. Best not to assume it is part of the solution. After the next accident, anywhere, Nuclear Power will be history book material, only; if a terrorist gets even close, the other ones will start to shut down. In all cases, security costs will go up.
    Do people think Uranium is a Renewable Power source?
    The other half of the problem is the Forest and the trees.
    Denmark gave us no details towards a solution, not even an Topic Outline. The only factor, I gather, was that nations do not want foreigners to verify they are not cheating, imagine that, they want funds but want no ff (fricking foreign) Inspectors to count the reduction on cut trees (there is sensitive and a logical problem on counting what was not done).
    I read NASA has satellite pictures, private companies enhanced, that can tell the accurate size of a forest down to a fraction of an acre. They can also measure and report humidity and type of vegetation. They have gone very far in this field. This should make the intrusion a non issue.
    Obviously, they can be paid for each new acre of trees every six months or every year no ff Inspectors to check their honesty.
    What if the payment is high enough and the country needs the money badly, how much forest could they grow? If the price is right, why not plant new forests in the USA, Mexico and Canada?
    The forest will determine the maximum amount of CO2 that can be tolerated. Since GW will burn forests first, it is the “Coal Mine Canary for the world”.
    Maybe, the number of forest acres required to compensate for any Carbon Emission can be used to set the Carbon Tax.
    Maybe, the Carbon Tax fund can be used to pay the yearly price for an acre of forest.
    Maybe, this is too complicated for politicians and will never sell.