Why two degrees really matters

Egg shell Big

Most CP readers know about the 2°C warming limit, but many don’t appreciate its full implications. This short essay by two of the analysts who completed the first comprehensive analysis of that limit back in 1989 elaborates on the most important of these implications.  Author bios and all references are at the end.  Koomey has been a friend and colleague for more than a decade and a half.  The figure comes from MetroNaturel.

Why two degrees really matters

Jonathan G. Koomey and Florentin Krause[i]

When the countries of the world meet for climate negotiations in Copenhagen this month, they will discuss how to prevent global temperatures from increasing more than 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels. This warming limit, accepted in principle by the leaders of the G8 countries in July,[ii] is more than just a number””it represents a way to think about the climate problem that can help us develop and evaluate options for solving it.

The current trajectory for greenhouse gas emissions would move the Earth by the middle of this century well outside the temperature range in which humanity evolved, marked by the 2-degree limit. This trend increases substantially the risk of dangerous, irreversible, and, perhaps, catastrophic changes in the global life support systems upon which we all depend.[iii] As the White House Science Advisor John Holdren aptly puts it, we’re “driving in a car with bad brakes towards a cliff in the fog.”[iv] The 2-degree limit is like a road sign warning us to avoid the cliff ahead.

Defining a warming limit implies a greenhouse gas budget, which is an upper limit to our cumulative emissions over the next 50 to 100 years. Such a budget encapsulates our scientific understanding of how emissions interact with the Earth’s climate and affect global temperatures. Some of the most significant greenhouse gases, like carbon dioxide, stay in the atmosphere for many decades,[v] which is why the budget is defined over the long term.

Acceptance of an emissions budget should focus the climate talks because it encourages discussion of how to allocate that budget among countries. Many argue that developing countries like China can legitimately claim much of the emissions budget because they have large populations and have consumed relatively small amounts of fossil fuels thus far. But developed countries like the United States can’t phase out greenhouse gases overnight. In addition, many emissions from emerging economies are attributable to the manufacture of exported goods. Discussion of a specific budget will help negotiators balance more effectively these complex issues of feasibility and equity.

The warming-limit approach is analogous to how businesses conduct planning under uncertainty: Set a long-term goal, then work backward to determine how to achieve it, modifying plans dynamically as developments dictate. It’s operationally much more useful than a target for a single year. In fact, it can be used to derive such targets over many years, once the budget is allocated to developed and developing countries. It also has advantages over conventional, forward-looking policy analyses, which are hamstrung by the inherent limitations of economic forecasting models in accurately predicting the future.[vi]

Using a warming limit in this way prompts us to ask questions like “What are the least expensive options for meeting the target?” or “How many emission-free power plants must be built per week to meet the target, and how much capital would that require?” or “How fast must energy efficiency improve to meet the target given projected economic growth?” The answers to such questions help us identify the options that are most cost-effective, feasible, and desirable, and allow us to envision the kind of world we want to create.

The 2-degree warming limit is demanding””it implies halting growth in absolute global greenhouse gas emissions within the next decade, with reductions of at least 50% by 2050 compared to 1990 levels, and larger reductions soon afterward.[vii] It also has other implications that most policy makers do not yet fully appreciate:

(1) We shouldn’t wait: Delaying action only eats up the emissions budget, locks in emissions-intensive infrastructure, and makes the required reductions much more costly and difficult later. Early action also brings the costs of technologies down through economies of scale and learning-by-doing, a fact usually ignored by ill-informed climate skeptics.

(2) We need to move quickly on many fronts: The rate of change in energy systems needed to stay within the budget[viii] will require broad societal mobilization, rapid innovation, and major investments in science, technology, and education not unlike those undertaken by the United States after the USSR launched Sputnik in 1957.[ix] One key to rapid change will be the development of new technologies that consumers prefer even if they initially carry a higher price””much like early fossil fuels, such as kerosene, were preferred to whale oil for lighting in the mid-1800s;[x]

(3) We can’t burn it all: More than half[xi] of the Earth’s remaining economically recoverable fossil fuel reserves must be kept in the ground to achieve climate stabilization (or, if burned, their carbon emissions will need to be stored securely). A price on carbon and significant reductions in the costs of low carbon technologies are the two most important means for achieving this difficult goal.

The 2-degree warming limit provides guideposts for a real solution to the climate problem, yielding insights available from no other approach. We’ll need to apply these insights, invest in a large portfolio of promising options, fail fast, and learn as rapidly as we can. There’s simply no more time to waste.

[i] Jonathan Koomey is a Visiting Professor at the Yale University’s School of Forestry and Environmental Studies, and Florentin Krause is a researcher living in Richmond, California. Krause was the principal investigator and Koomey was one of two other coauthors of the first systematic attempt to evaluate the implications of a warming limit-based approach to addressing the climate problem (Florentin Krause, Wilfred Bach, and Jonathan G. Koomey. 1989. From Warming Fate to Warming Limit: Benchmarks to a Global Climate Convention. El Cerrito, CA: International Project for Sustainable Energy Paths. <>). It was republished in 1992 as Florentin Krause, Wilfred Bach, and Jonathan G. Koomey. 1992. Energy Policy in the Greenhouse. NY, NY: John Wiley and Sons.

[ii] Baker, Peter. 2009. “Poorer Nations Reject a Target on Emission Cut.” The New York Times. New York, NY. July 9. <> and ENS. 2009. “G8 Leaders Aim to Hold Global Warming Below Two Degrees Celsius.” Environmental News Service. Seattle, WA. July 8. <>

[iii] For discussion of historical temperatures and the 2-degree limit see Chapter 1 in Krause et al. 1992 in footnote i above.

For more recent assessments of predicted impacts see the Working Group I and Working Group II reports from the IPCC’s Fourth Assessment Report.

[iv] See the interview with White House Science Advisor John Holdren here and here.

[v] See the Intergovernmental Panel on Climate Change Fourth Assessment Report, The Physical Science Basis.

[vi] See Craig, Paul, Ashok Gadgil, and Jonathan Koomey. 2002. “What Can History Teach Us?: A Retrospective Analysis of Long-term Energy Forecasts for the U.S.” In Annual Review of Energy and the Environment 2002. Edited by R. H. Socolow, D. Anderson and J. Harte. Palo Alto, CA: Annual Reviews, Inc. (also LBNL-50498). pp. 83-118, Koomey, Jonathan G., Paul Craig, Ashok Gadgil, and David Lorenzetti. 2003. “Improving long-range energy modeling: A plea for historical retrospectives.” The Energy Journal (also LBNL-52448). vol. 24, no. 4. October. pp. 75-92, and DeCanio, Stephen J. 2003. Economic Models of Climate Change: A Critique. Basingstoke, UK: Palgrave-Macmillan. Economic models are far less reliable than the climate models because the underlying structural attributes of economic systems are not constant in the same way that physical systems are constant.

[vii] Meinshausen, Malte, Nicolai Meinshausen, William Hare, Sarah C. B. Raper, Katja Frieler, Reto Knutti, David Frame, and Myles R. Allen. 2009. “Greenhouse-gas emission targets for limiting global warming to 2 degrees C.” Nature. vol. 458, April 30. pp. 1158-1162.

[viii] See Chapter 6 of Krause et al. 1992 (in footnote i) for analysis of logistic feasibility.

[ix] The first use of the Sputnik analogy of which we’re aware was Koomey’s testimony before the Joint Economic Committee of the U.S. Congress in July 2008 (Testimony of Jonathan Koomey, Ph.D. for a hearing on “Efficiency: The Hidden Secret to Solving Our Energy Crisis“. Joint Economic Committee of the U.S. Congress. U.S. Congress. Washington, DC: U.S. Congress. July 30, 2008.). Tom Friedman of the New York Times started using this analogy independently in September 2009.

[x] Lovins, Amory B., E. Kyle Datta, Odd-Even Bustnes, Jonathan G. Koomey, and Nathan J. Glasgow. 2004. Winning the Oil Endgame: Innovation for Profits, Jobs, and Security. Old Snowmass, Colorado: Rocky Mountain Institute. September. <

[xi] See Chapter 4 of Krause et al. 1992 (in footnote i) and Meinshausen et al. 2009 (in footnote vi).

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24 Responses to Why two degrees really matters

  1. This would be perfect, if only it included a point that I think the majority of information consumers do not understand- what marks the urgency of the 2 degree point.

    The thing that woke me up to climate change was the recognition of that tipping point, a point at which we are taken out of the driver’s seat and are on cruise-control towards oblivion. After 2 degrees celsius, positive feedback loops begin taking effect that render us even more at the mercy of events wholly out of our control than we already are, and events that are civilization-ending in scale over the long-term. This is something I think people can identify with (as much as any of us can ‘identify’ with something so cosmic as climate change)- a point at which we lose control. And it gives the thing the urgency it requires. I wish they had made that point, if we consider this to be for a general (more climate-ignorant) audience.

  2. David B. Benson says:

    For the effects at each additional 1 K of warming, read Mark Lynas’s “Six Degrees”. Here is a link to a review:

    Note that we already have about 0.7–0.8 K of warming and the effects given for 1 K, from the paleoclimate literature, are already beginning to occur.

  3. Dano says:


    it does include the reason: 2º C warmer is beyond anything modern human society knows. Warmer than anything we have experienced.

    This is why the limit was chosen.

    As far as the feedback loops, I am graduate-level trained in ecology at a leading uni. Maybe these things after 2º will indeed be more likely to happen, but I’m unaware of the literature coming down on that number positively with a consensus.



  4. pete best says:

    I cannot see it personally. To imagine that fossil fuel usage wont be expanding over the next 30-40 years to meet the world ever growing energy needs seems plausable but then actually cutting back on present fossil fuel usage is difficult to imagine. The reasons are numerous and often political.

    Most energy sources of the scale required often sit in deserts and are a longway from where the energy will be used. HVDC cables maybe but that makes Governments nervous due to energy security issues etc.

    Tying all of these energy sources together in new grids that need to be built pan continentally is not either easy or cheap to undertake. New Energy sources and energy burning devices are in their infancy and market forces are at work here. People like petrol cars and hence getting a real shift in enplasis over to electric vehicles is not easy.

  5. Worth noting that the 2 degree number is old, and according to many no longer a valuable guide to where the danger lies. After all, if we now know (as we didn’t when 2 degrees was first put forward) that 0.8 degrees celsius melts the Arctic, do we really want to find out what two degrees will do? The slogan for Copenhagen from 40 or 50 of the most vulnerable nations? “1.5 to Stay Alive.”

    thanks for this good piece

  6. Leif says:

    Pete Best: For all the reasons listed above and more, it appears to me that we need to concentrate on point of use sources of energy along with efficiency. There may be a bit more cost up front but one gets to save line loss as well as security costs. I would think that point of use systems could be readily mass produced and deployment would help the unemployment picture. Home generation along with the family car for additional storage would make for a very nice package.

  7. Leif says:

    Pete Best: In addition point of use is much more compatible to the existing grid. Not that grid improvements are not worth while in their own right. Point of use power sources also allow evolution to progress without having to commit huge amounts of money to unproven systems. Public acceptance might be improved as well as an integrated power/transportation system that was paid for out of existing energy costs with the profits bankable upon ownership… What’s not to like?

  8. Pete Best,

    You have summarized some of the reasons why this will be a difficult challenge, but using this way of framing the problem (ie the warming limit approach) makes it clear that we have little choice.

    We have plenty of options for making a serious dent in the climate problem, and many of those make sense for other reasons than climate–the difficult political issues for achieving larger reductions can be tackled along the way, opening up more possibilities. There are sufficient amounts of cost effective wind, gas fired combined cycle, efficiency, and cogeneration resources to displace a substantial fraction of existing U.S coal plants, reducing greenhouse gas emissions and eliminating significant criteria pollutant emissions (because many of those plants were “grandfathered” under the clean air act and have few or no pollution controls). As costs come down for photovoltaic panels those too can begin to come into the mix. And by changing the way we operate the utility grid, building supply-side technologies with rapid ramp rates (to respond better to changes in load and intermittent power production), implementing time of use and real time pricing on a wide scale, using weather forecasting to estimate intermittent production ahead of time, and improving our grid control technologies/strategies we can modernize the grid and enable us to incorporate even more intermittent resources in the years ahead. That effort will yield other advantages, also, like more flexibility in operating the grid in the face of unexpected events. See the Rocky Mountain Institute book called “Small is profitable” for more examples.

    You are absolutely right that we need to build more transmission lines to bring renewable power to the cities, but this is not a technical challenge but a political one. The people in Iowa are very happy to have large wind farms and the people in Chicago will be happy to buy the renewable electricity–that creates the possibility for a deal, but we’re going to have to work through some difficult issues to get there. That shouldn’t stop us from starting to build wind plants in places that don’t require big new transmissions investments.

    One of the key points of the posting is that our choices now affect our choices later. If we invest now in building new technologies, that drives costs down and builds capacity for further growth in those technologies, which enable even more growth in the future. If we don’t start down the path of building alternatives, the “lock in” effect constrains our choices.

    And you are right that people like petrol cars, which is why I’m convinced that to make low emission technologies permeate the society we’ll need to build them in a way that people want them for more than just their environmental attributes. They need to be better all the way around, by focusing on what Amory Lovins calls “whole system, clean slate redesign”, so that people just want them. If we do that, we can make this transformation of the energy system happen.


  9. Bill McKibben,

    You are absolutely right that there are many good reasons to argue for staying well below the 2 degree limit but that limit is the one that we analyzed and the one that the politicians accepted this year, so that’s what we focused on for the essay.

    The more important point is that the warming limit approach is a way of understanding the problem that gives real insight, and the exact level of the target is less critical. Working backwards from the limit is ultimately a better way to think about this issue than trying to project our “warming fate” if we undertake certain policy actions now. The choice of warming limit is ultimately a normative value choice, one that expresses our preferences for avoiding catastrophic risks that would leave a substantially altered world for our children and grandchildren and put humanity’s future in question. I find the arguments for even stronger precautionary actions persuasive, but we need to figure out what we can really do, and soon.

    The issue now is getting started down a path that reduces global emissions in the next ten years. I believe strongly that it is impossible in principle to accurately calculate costs and benefits 100 years from now, but we can do so for options sitting in front of us right now, so let’s start there and begin learning about what works (that’s what I mean by line towards the end of the essay about investing in a portfolio of options and failing fast). Once we start down that path it will become clear just what possibilities are opened up by our earlier action. The world is path dependent and pervaded by increasing returns to scale, which makes the future ours to create. We just need to seize the moment and make it happen.

  10. Alex Evans says:

    Absolutely right that we need to get a move on if we want to limit global average temperature increase to two degrees C – which introduces the question of when global emissions need to peak by.

    IPCC Chair Rajendra Pachauri says that date is 2015. The main development NGOs working on climate change – including Oxfam and Avaaz – agree.

    Which raises the question: why the hell is Climate Action Network, the main federation of environmental NGOs, saying that any time up to *2017* is fine – when the IPCC 4th Assessment Report is clear that this puts us in the zone for temperature increase of 2.4-2.8 degrees C? Why are key organisations like WWF backing them up?

    It’s critical that these NGOs feel the heat on this and get their positions in line with IPCC recommendations *right now*, before Copenhagen kicks off.

    If you support a CAN member NGO, then you may wish to call them tomorrow morning to ask their position; over at Global Dashboard, we’re suggesting that supporters cancel their subscriptions to any NGOs endorsing a peak date later than 2015. We simply should not be having to expend scarce advocacy bandwidth persuading major NGOs to get basic fundamentals like this right with Copenhagen underway.

  11. Simon D says:

    Nowhere here has anyone explained why the warming limit should be exactly 2 degrees. That’s a shame. We get ourselves into trouble by not explaining that it is a normative choice, based on analyses of scientific results and decisions about what impacts are deemed acceptable, rather than a direct outcome of the science. For one, climate science couldn’t possible give an exact number, just a frequency distribution of possible values; and even science could give an exact number, it’d be an amazing coincidence that it turned out to be an integer.

  12. Cynthia says:

    According to a recent newspaper article, the arctic sea ice is so thin that scientists can’t even walk on it. So basically, the ice will be all gone next year? When there’s no more ice, the temperature in the arctic region will increase dramatically– an extra 5 degrees, according to scientists. The permafrost, which is already in a state of near collapse and emitting around 50 million tons of methane gas per year, will really defrost and all hell break lose, it seems!

    The article explains why it’s important to have a goal of limiting emissions to 2 degrees, even if that goal isn’t sufficient to actually prevent catastrophe. But still, doesn’t the fact that the arctic ice is so thin, mean that we have only a year or less to make drastic cuts, on the level of WW2 effort? And if so, why is no one discussing that? Don’t we need futher measures in conjunction with the goals set by the IPCC?

  13. James Newberry says:

    Small point: We are at or approaching 450 ppm carbon dioxide equivalent NOW. The earth will respond to this concentration. The dramatic climate change effects we are witnessing today are due to gases released decades ago. It is therefore my judgement that we are headed for a two degree planetary rise based on past releases. Consider the positive feedback of the coming summer meltdown of all Arctic Ice.

    We seem to be on the Titanic wondering if we should take the throttle off full steam ahead. Their best hour (with magnificent machinery) was just before disaster. In an opposing way, ice (melting of) may be the common factor in this unfolding global tragedy, unless we act strongly this year.

  14. Cynthia says:

    To Joe Romm: Is it too late to save the arctic? If millions of us marched on down town Washington and demanded WW2 efforts and governments finally agreed to make an all-out effort, would it be too late? Don’t we have only about a year left before all the sea ice is gone?

    [JR: Ice free summers seem inevitable, yes. I have a bet for 2020, which I still like. Sooner is possible, as is later, though not much past 2030. Right now, your focus shouldn’t be marching, it should be swing Senators!]

  15. Simon D: See my comment 8 about the normative nature of the choice of 2 degrees. All choices involve value judgments (see Chapter 19 “Distinguish Facts from Values” in my book Turning Numbers into Knowledge for more discussion of this point: In this case it was the normative choice of the G8 countries who chose that limit, after years of intense advocacy by the European countries and the Pacific Island states.

    In this case, the normative judgment is up front (the choice of some warming limit), and it embodies society’s risk tolerance given our current state of knowledge. As we learn more, we will surely adjust our assessment of the risks, and right now it is clear that the earth is warming a whole lot faster than the IPCC predicted even a couple of years ago (see the Copenhagen Diagnosis paper at; I know Joe did a blog posting about this study also).

    So two degrees is what the political leaders are able to accept right now. It is based on the historical record, which gives us some idea of the temperature range within which humanity evolved, but you’re right, it collapses a great deal of scientific complexity into one round number. That, I’m afraid, is the nature of translating science into policy a fair amount of the time.

    I feel strongly that we need to take an evolutionary approach to this problem and the accepted limit will surely change. For simple problems people can and should collect all information before making a decision, but for climate that approach just won’t work. Once we’ve determined that the risks of adding more greenhouse gases to the atmosphere are too high (that’s a value choice that virtually the entire world has now made), we need to start acting to reduce those emissions and learn from that experience. We also need to measure the impacts of current warming, and if things are heating up much faster than initially predicted (and they seem to be) then that lends additional urgency to moving more quickly.

    The experience of most technology policy is that the initial estimates of the costs of action are often too high (For example, see Harrington, Winston, Richard D. Morgenstern, and Peter Nelson. 1999. On the Accuracy of Regulatory Cost Estimates. Washington, DC: Resources for the Future. Discussion Paper 99-18. January and Goodstein, Eban, and Hart Hodges. 1997. “Polluted Data.” In The American Prospect. November-December. (free trial)). This result makes sense because people and institutions are innovative in the pursuit of profit, which is one of the reasons why we need to use markets to help solve the climate problem.

    The ironic thing is that virtually all of the economic models attempting to estimate costs embed rigidities in the forecasts that are not inherent in economic systems. In fact, it is the very flexibility of those systems (combined with the inherent unpredictability of pivotal events) that make it impossible in principle to estimate costs and benefits 100 years from now (see footnote vi above for sources documenting this claim). We can estimate costs now for currently available options, though, and there are plenty of those available to us (see post 7 above for more discussion of this point).

  16. Roger says:

    Writing from Copenhagen, I think Cynthia is right, and Joe (forgive me) is wrong on this point about the root of our unique, US-rooted climate constipation.

    Swing senators are the apparent problem, but behind them are their constituents who don´t get it. These oblivious constituents are the ones that prevent the nervous, hungry-to-be-re-elected swing senators from supporting stronger climate legislation. Senator John Kerry said as much in a recent conference call to a group of us Massachusetts climate activists.

    We need to somehow get word to Americans about the severity of the climate problem. We must continue to urge President Obama to make a strongly-worded `State of the Climate´ address to oblivious Americans as soon as possible.

    If that doesn´t happen soon, then I think we need to take to all head to Washington, despite the carbon cost. There is just too much at stake here to keep going slow!

    Anyhow, it is great to be here, where people on the streets get it, where heavy insulation is mandated, where energy conservation is a given, and where one can talk freely about the need for stronger climate agreements without seeming to be from another planet!

  17. Leif says:

    I posted this link on another article but it applies here as well.
    CO2 warming stronger than thought. New research science/ articles/ 2009/ 12/ 07/ 2763819.htm
    In reality no one knows what a safe level of green house gas is other than the ~280 ppm of the past. Anything else is a crap shot.

  18. Cynthia says:

    Roger, I can’t imagine Obama coming before the public and talking in a WW2 fashion unless we show him how strongly we feel–as in thousands marching in Washington. They’re already marching in Europe. The arctic sea ice is so thin you can’t walk on it! Male polar bears are eating their young!

    In his public address before taking office, Obama emphasized that one person can’t do it all, that we all have to become involved. It would be so much easier for him to publicly address the issue of climate change in a WW2 manner if we had massive marches in Washington. That’s how the Vietnam War ended, slavery ended, etc,– when the people pushed strongly against the tides of evil.

    As for senators in Washington, our newspaper stated that most of the republicans who are supposed to vote on the climate bill have large investments in fossil fuels. Greed obviously blinds.

    There are about 2,500 energy lobbyists in Washington. They’re all hell bent on keeping the status quo. We’re supposed to have one equal vote. Not so! The only way we can win is if we all come together as one force. The Internet can make it happen! I’m just not sure how we could pull it off!

  19. Doug Meyer says:

    Progressives are getting nowhere because the public thinks of them as environmentalists trying to save the planet (see image above or Joe’s Time Magazine award earlier this year) while, as Joe understands better than most, progressives are not primarily interested in the environment. This post contains not one mention of, for example, 30% of all species on Earth going extinct with a temperature rise of 2 deg C. No, progressives are all about trying to “save” the very civilization responsible for destroying the Earth. (Bit of a moral problem there that most of us rednecks can smell out underneath the economic and political thrust of this post.) Progressives rightly point out flaws with the media’s coverage of global warming while ignoring the biggest one: the carbon already in the atmosphere means it’s too late for the environment.

    Progressives are using the public’s ignorance of the committed warming’s impacts for political gain. Sound familiar?

    [JR: That last line is silly. Certainly not what I think or any progressive’s I know think.]

  20. Michael hauber says:

    I don’t think anyone has a clue whether 2 degrees, or 1 or 5 is the threshold for catastrophe. So many unknowns. Certainly the argument that human’s haven’t experienced anything higher is irrelevant. What if another 0.5 degrees temperature increase reduces agricultural productivity by 30%? What would be the impacts on our world today? A few centuries ago there were many less people on our planet and we could probably just farm 30% more land to account for this. But could we do that today? Or in 50 years?

    And on the other side we don’t know what breakthroughs our technology may make in the future. Will we be able to genetically engineer a crop that will be able to take advantage of the extra heat and Co2 to make more food? Certainly not something we can count on, and not something we can rule out.

    We don’t know how much warming the earth can really afford. That to me suggests we need to be making every effort to reduce warming to whatever level is achievable. If we cap and trade to 2 degrees, and make a massive technological breakthrough in solar that makes this easy, then the pressure to reduce Co2 will be off and we might easily cap warming at say 1.8 degrees. But what if we then find that everything falls to pieces at 1.5 degrees?

    In contrast if we have a flat carbon tax any breakthrough that would make 2 degrees easy would still have a tax in place to encourage further effort to reduce the warming to an even lower level.

  21. Roger says:

    Cynthia, There’s a very good chance you’re right, unfortunately.

    With so much at stake, we should be ready to ‘risk’ doing a march on Washington, even though it might not be needed. Who’s ready to step up to the plate to set a date and start organizing this? Shall we do it in March? We need to get all of the thousands of serious US climate groups marching to the same drum, on the same day, to the same place.

    Perhaps the seeds can be planted here at the conference in Copenhagen!

  22. Doug Meyer,

    You have made assumptions about our motivations that are not correct. We debated talking about many of the impacts of exceeding the two degree limit and decided not to get into too much detail, instead focusing on the ways that using the 2 degree warming limit can help focus our thinking on solutions Joe, the IPCC, and others have talked in great depth about the impacts of climate change on ecosystems as well as on humanity, and there was no need to spend precious words in a short essay going into more detail.

    Florentin and I care deeply about the earth (and other species), not just about human society. That’s why we’ve been working on solving the climate problem since the mid 1980s (back before it was “cool” to do so).

    And it’s not too late to avoid the catastrophic impacts, but you are correct that we are already committed to significant warming. The question is how much effort we’ll need to avoid those catastrophic impacts.

    So please don’t ascribe motivations to us based on your suppositions. Generalizations are occasionally useful, but they often lead one to miss the truth, and they inhibit real dialogue.

  23. Michael Hauber,

    You are correct that nobody knows for sure that a warming limit of 2 degrees C will avoid all catastrophic impacts, but that uncertainty should make us even more cautious and eager to reduce emissions
    The uncertainties you identify are exactly why I advocate an evolutionary and adaptive approach to solving the problem (see my comment 14 above). Our inability to predict the future accurately (for either costs or benefits) means we need to try many options and learn quickly which options work well and which don’t. If climate change seems to be accelerating, we’ll need to redouble our efforts and move even more quickly to solve the problem.

    However, your post seems to miss the underlying dynamics of technical systems of this type. Eliminating fossil fuels will require developing technologies that are simply better than what they replace, and once we are on the path to substantially reducing use of carbon-based fuels, we won’t just stop at some arbitrary limit. People will eventually decide that combustion itself is the problem, and at that point (given the rapidity with which the non-fossil energy sources are evolving and will continue to evolve), it’s only a matter of time before combustion of those fuels becomes a socially undesirable AND uneconomic choice.

    Even in the framework of a cap and trade system, if it’s so easy to reduce emissions that the price of permits falls to a very low level, it’s time to reduce the cap until the carbon price is again high enough to encourage continued switching away from fossil-based fuels. It should not be a static cap, it needs to decline over time, on a pre-specified path in the beginning (to give certainty to businesses investing in solutions) and then in response to extraordinary events (like the collapse in permit prices that you posit).

    There are advantages to using a tax instead of cap and trade, and many economists favor the tax. The enforcement costs are a lot lower (very small if the tax is levied high up in the supply chain for fossil fuels) and there’s little possibility for people avoiding the tax. But the argument for the cap and trade system is that we care about quantities of emissions, so why not set the quantities and let the market equilibrate to the cost effective level? This creates uncertainties in prices, which businesses don’t like, but it does have the nice feature of dynamic adaptation to new developments. Of course, markets of any kind are subject to manipulation (like that which nearly brought down the world’s financial system last year) so the tax is preferable from that perspective as well. Of course, the right question from my pragmatic perspective is “which way of pricing carbon will get 60 votes in the Senate?” We’ve can’t let the perfect be the enemy of the good, and we need to move quickly, as the 2 degree limit makes clear.

  24. Cynthia says:

    Roger, thanks for replying. I thought that if we could somehow email one another we could work out the details. Otherwise, we may lose track of each other’s messages. There are a few others who post on this website who also seem interested. We could invite them to help with the plans.

    Yep, we could contact climate groups, environmental organizations, universities, young people.

    As far as the date goes, I thought we could first write to different organizations and different establishments and let them know of our intentions, the exact reason why it’s so important to march and tell them we will set a date later. That will give us time to organize. (Perhaps your idea is better, that was just my idea.)

    I’ve already written a letter we could send out to them. However, you or anyone could else could write it instead (or help improve it!)

    I like your idea about Copenhagen! Perhaps we should set a date so everyone there can plan.

    Roger, I DO think it’s needed. I’m no scientist but climatic events are happening faster and faster and if the arctic sea ice goes, I don’t think there will be much chance for our earth to survive– all the variety of species, trees, etc. They’re dieing now! It would be a tragedy. And us too! Jim Hansen suggested we march. He said we can’t lose the arctic! We need WW2 effort, but all we get from politicians is crumbs.