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

In this post I will lay out ‘the solution’ to global warming.

This post is an update of a 2008 analysis I revised in 2009. A 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 as a vindication of this overall analysis.

Stabilizing atmospheric concentrations of carbon dioxide at 450 ppm or lower is not politically possible today — not even close — but is certainly achievable from an economic and technological perspective, as I and others have said for years.

Humanity has only two paths forward at this point. Either we voluntarily switch to a low-carbon, low-oil, low-net water use, low-net-material use economy over the next two decades or the post-Ponzi-scheme-collapse forces us to do so circa 2030. The only difference between the two paths is that the first one spares our children and grandchildren and countless future generations untold misery (see “Intro to global warming impacts: Hell and High Water” and “A stunning year in climate science reveals that human civilization is on the precipice”).


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 Princeton website here). These 12–14 wedges are my focus here.

The reason that we need twice as many wedges as Princeton’s Pacala and Socolow have said we need was explained here. 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. For a longer discussion on cost, see “Introduction to climate economics: Why even strong climate action has such a low total cost.”

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, though obviously the strategies that are most scalable and have the most co-benefits and fewest negative impacts should be favored.


Princeton’s Pacala and Socolow proposed that this could be done over 50 years, but that is almost certainly too slow. Sadly, there is little prospect that the aggressive deployment will begin in the next few years (see “The failed presidency of Barack Obama, Part 2”).

We’re now over 30 billion tons of carbon dioxide emissions a year (more than 8 billion tons of carbon) “” 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, how quickly peak oil kicks in, and the extent to which other countries around the world keep their substantial Copenhagen/Cancun commitments in the absence of a global agreement. We have to average below 18 billion tons of CO2 (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”).

[A note on units: One ton of carbon equals 44/12 = 11/3 = 3.67 tons of carbon dioxide (see “The biggest source of mistakes: C vs. CO2”). A billion tons is a Gigaton (Gt). By default, I will use GtCO2 and put GtC equivalent in parentheses.]

We need to peak around 2020, 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. You may view this as politically implausible now, which it is. We could, of course, peak in say 2025, but then we have to drop even faster and unbuild more polluting, inefficient infrastructure.

Delay is very risky and expensive. In releasing its 2009 Energy Outloook, the executive director of the International Energy Agency said last year, “The message is simple and stark: if the world continues on the basis of today’s energy and climate policies, the consequences of climate change will be severe.” They explain, “we need to act urgently and now. Every year of delay adds an extra USD 500 billion to the investment needed between 2010 and 2030 in the energy sector”.The risk comes if we wait so long that we set off amplifying carbon cycle feedbacks that undermine mitigation efforts and shoot us quickly to very high levels of CO2 (see Royal Society special issue details ‘hellish vision’ of 7°F (4°C) world — which we may face in the 2060s!)

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 and get to zero as soon as possible after that 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 the first phase 1, which I now expect begins circa 2020, the world finally gets serious about avoiding catastrophic global warming impacts (i.e. Hell and High Water). We increasingly embrace a rising price for carbon dioxide and a very aggressive technology deployment effort.

In phase 2, 2030 to 2050, after countless 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 “Veterans Day, 2030” 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. 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 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 to 1 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 in aninterview.

I am more bullish about PV and vehicle efficiency these days, based on recent technological advances.

I have been skeptical for a long time that we could do more than 1 wedge of CCS (see “Is coal with carbon capture and storage a core climate solution?”). Research — and reality — in the last year have increased that skepticism among many experts I know:

Ironically, the death of a climate bill for the foreseeable future may prove fatal to CCS. It is far less likely it will be ready when it is needed, since it probably takes 10 years of serious effort before CCS is even plausible to scale up.

The 1 wedge of nuclear includes a half wedge of next generation nuclear post-2030. Why not more than 1 wedge? Based on a 2007 post 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. It is also increasingly unlikely 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: I am not proposing to build all those nuclear plants nor do I think we would need to — but with CCS becoming less plausible for delivering a wedge, let alone more, nuclear may take up some of the slack. Also, I do 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.

This is not to say the two wind power wedges (4000 GW peak total) would be easy “” but the world did build 16 GW of wind in the first half of 2010. 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 mistakenly think we need a lot more wedges. I explain why this is a mistaken view in Part 2.5: The fuzzy math of the stabilization wedges [warning: only for hard-core wonks].

BUT if we do delay a full decade until 2020 before getting serious, then rather than deploying more wedges, the (somewhat) more plausible strategy is to deploy them faster, over 3 decades — an effort that rivals the homefront effort in World War II, but lasting far longer and encompassing the world. That’s why climate mitigation (and adaptation) will become the primary driver for the economic policy of every major country within a quarter century (see “Real adaptation is as politically tough as real mitigation, but much more expensive and not as effective in reducing future misery”)

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 explain at length here (see “The breakthrough technology illusion”). Increasingly R&D is very important, as I’ve argued for two decades, but rapid deployment is the sine qua non for averting multiple ever-worsening catastrophes.

The bottom line is that give or take a wedge or two, we are likely to do most of what I lay out above sooner or later. Let’s work hard to make sure it’s sooner.