[Update: 22 January 2009] Some of the information in the post below is inaccurate. Namely, it implies that some level of continuous emissions is compatible with climate stabilization. In fact, stabilizing climate required humanity to have zero net emissions in the long term. For more about this, see this post.
On this blog, I have frequently cited a figure of about 750kg of carbon dioxide per person per year as sustainable. This is just what you get when you divide the approximate level of sustainable emissions (about 5,000 megatonnes) by the number of people alive on Earth. If each person emitted that much, the net radiative forcing effect of anthropogenic emissions would be approximately zero. That means the sum of the concentrations of all greenhouse gasses, multiplied by their global warming potential, would be in balance with the capacity of the planet to absorb those gasses.
Of course, suddenly achieving the transition to 750kg each would be extremely painful. Thankfully, achieving it instantly is not necessary. Right now, the atmospheric concentration of carbon dioxide (the most important greenhouse gas) is about 383 ppm. That compares with 280 ppm at the time of the Industrial Revolution. Scientists disagree about how much that concentration can rise before extremely harmful effects start to manifest themselves. The highest number generally suggested by reasonable people is 550 ppm, a more mainstream figure is 450 ppm, and some people even argue that we have already emitted enough that very harmful effects are inevitable, once lags in the climate system are overcome. At present, unsustainable global emissions are increasing the global concentration of carbon dioxide by about 2 ppm a year.
Acknowledging the uncertainty, let’s take 450 ppm as a best guess. That means we have about 67 ppm of shoulder room left. It is vital to note that this isn’t shoulder room for total emissions to rise; in the long run, they absolutely must fall dramatically. It is shoulder room in which we can keep emitting above unsustainable levels without wrecking the planet. The situation is akin to being in a lifeboat in a hot, dry climate with a barrel of water and a solar still that produces a small amount of water per day. The 750kg each is the output from the still. The 67 ppm is approximately how much we have left in the barrel. The question now becomes how to divide it. Here are some possibilities:
- Continued unsustainable emissions in the developed world
- Continued and increasing unsustainable emissions in the developing world
- Additional security against abrupt or runaway change
We also have a choice about how to divide the use of barrel water across time. We might decide to drink lots of it in the early days, leaving less for later on. We might decide to save as much as we can. Of course, our capacity to do the latter is somewhat limited by the tragedy of the commons. It’s like there are a whole bunch of strangers in the lifeboat and any one can drink from the barrel without the others being able to stop them. You might end up with everyone trying to grab all they can early, even if saving most of the water for later would produce the best outcome for everyone.
Will we be able to find a way to moderate how much each person takes from the barrel? How much should we be willing to suffer in able to conserve some water for the future, or as a hedge against the possibility that 450 ppm is actually too high? These are among the toughest and most pressing questions in global climate change policymaking.
Page 9 of the Summary for Policymakers of the Climate Change 2007: Synthesis Report provides some sense of the uncertainty surrounding 450ppm as a target. It shows various stabilization scenarios (each based on a different stabilization concentration target) and ranges in which likely effects may manifest themselves.
This post is partly a response to an ongoing debate with Tristan. Part of it can be found in this comment thread.
Tristan also wrote an entry about it here:
An argument concerning the morality of climate change
See also: Global equity
I have absolutely no qualms with your science. However, this simply
does not result in a moral imperative to produce only 750kg of carbon
dioxide. At very least I would think we could adopt a Rawlsian
approach. I’m not going to pretend that I know the outcome, but I
would expect it to be something like a carbon-trading network adjusted
to benefit the least well off to the maximum degree. Perhaps this
would mean an open market where people could sell and buy carbon
shares from a centralized bank, but the centralized bank would pay
progressively more or less for shares depending on how well off people
were.
But of course, this would have to obey the Kantian imperative – which
is that the moral action must be non-contradictory if it is to be
universalizable. In other words, if everyone follows the universal
imperative, this must not create conditions in which no one can follow
the imperative. For example, whatever solution we implement to reduce
carbon emissions to a sustainable level, following that solution must
not produce the impossibility of following the solution. In other
words, if the solution throws us into a recession that necessitates
everyone using coal to heat their homes, this is a contradictory
solution. I’m not a science or policy analyst, but I would assume that
problems of this kind would be important to the drafting of policy
with relation to scientific need (it’s akin to the problem of
externality, except the externality in this case has internal
relavence to the issue).
But this ends me with the distinction between the moral imperative and
ethics. The history of morality with the exception of Hegel has been
the attempt to unify morality and ethics. Kant’s catagorical
imperative is probably the best try at it. However, I don’t think its
a sustainable unification – we need to recognize that people need the
right to make their own decisions, to question the authority of the
state, and on the other hand, the state needs the ability to set the
conditions under which decisions are made so that people’s subjective
interests align with universal (or “common”) interests.
Tristan,
It’s entirely possible that a Rawlsian approach would demand that people in the rich world emit less than 750kg, for the benefit of people in developing states and future generations.
In other words, if the solution throws us into a recession that necessitates everyone using coal to heat their homes, this is a contradictory solution.
The danger doesn’t really consist of people willingly slamming the brakes too quickly. Even people who understand the problem well are still out buying second cars and flying to Sydney for vacations. The risk of inaction leading to tragedy is a lot greater than the danger of excessive early action leading to economic turmoil.
[W]e need to recognize that people need the right to make their own decisions, to question the authority of the state, and on the other hand, the state needs the ability to set the conditions under which decisions are made so that people’s subjective interests align with universal (or “common”) interests.
This is true, and the dynamic is an important one. I don’t think we can rely on voluntary actions to get to a sustainable low-carbon economy. This is primarily due to the huge market failures involved: particularly the unlimited power that those alive today have over choices that will affect future generations much more acutely than us. The post above isn’t a pragmatic argument about the approach we should take (for an example of that, see this post), it’s a description of what is at stake and an elaboration of the important issue of dividing both sustainable emissions and the remaining stock of safe ‘shoulder’ emissions.
Saying “we can’t reduce emissions because if we do it instantly, it will wreck the economy completely” is a bit similar to saying “we may be plummeting towards the ground, but we cannot open our parachutes because if we were to stop instantly, the acceleration would kill us.” At best, we are talking about deploying the pilot chute which will start the process of unfurling the technical, infrastructure, and behavioural changes that will eventually produce a real low-carbon economy.
I never said we can’t reduce emissions. What I said was we can’t make “reduce your emisions” a moral claim, because if people actually followed the kind of painless reductions we would recommend to them, turmoil would ensue. And as much as we like to say you can’t weigh gold bars against the whole world, we have little chance of saving both us and the whole world without gold bars. It’s easy to forget what gold bars mean – they mean human labour. Without people willing to work, to develop new technologies, there is zero chance of saving anything. We need gold bars and the earth.
The U.S. economy, as currently configured, is destroying the planet. We are responsible for the lion’s share of a great many global problems, including being both the largest historical carbon polluter and the leading source of global emissions today
In addition, for the several billion people in the developing world who are rapidly climbing out of poverty, our lifestyles are the measure of prosperity. If they replicate the American way of life several billion more times, our goose is cooked. The natural systems on which we depend cannot survive the tidal wave of pollution and ecosystem degradation it would take to enrich billions of people using current technologies, designs and lifestyle choices. And we’re not going to talk people out of pursuing a more affluent life: it’s insane to think that we can talk them out of pursuing affluence while we waste our way to wealth. If we’re serious about saving the planet, we need to help them create better alternatives.
The single best way we can do that is to lead by example. By embracing our own models of sustainably prosperous living, we would do two things: we’d help change the cultural messaging about what prosperity really means, and we’d create some (perhaps many) of technologies and designs other countries will need to invent their own models. More importantly, we’d show that we’re taking responsibility for the massive burden we’re already placing on the planet, and show that we’re again willing to show leadership on global issues. That alone might lead to reinvigorated global negotiations on a whole host of key problems.
“The single best way we can do that is to lead by example. ”
I’m fully open to the possibility that this is the best thing we can do (for the sake of mitigating climate change). But that does not make it a moral imperative. There are lots of things which are good for us to do, or even which are obligations, which are not moral laws. To test for a moral law, it must be the case that everyone could follow it strictly without producing a contradiction. It’s just a funny thing that our economy runs on excess, and that if we were all to immediately stop indulging, it would collapse, and we wouldn’t have money to spend on renewable energies. This just proves that “reduce your emissions” is a polemic claim, one that we would like lots of people to go along with. But it isn’t moral because it doesn’t pass the universalizability test. Now, whether your personal actions pass the universalizability test is another matter – it might be the case that everyone in your situation ought do what you are doing, and this might not produce a contradiction, because there are few of you (one, in fact). However, the danger is in saying its a moral claim in general, because it produces a contradiction.
The arithmetic is becoming clearer. If the rich nations continue to grow in income and the poor ones systematically narrow the income gap with successful development, by 2050 the global economy might increase sixfold and global energy use roughly fourfold. Today’s anthropogenic carbon dioxide (CO2) emissions are around 36 billion tons annually, of which 29 billion are the result of fossil-fuel combustion and industrial processes, and another seven billion or so are the result of tropical deforestation.
Roughly speaking, every 30 billion tons of emissions raises CO2 levels by around two parts per million (ppm). The current atmospheric concentration of CO2 is around 380 ppm, up from 280 ppm at the start of the industrial era in 1800. Thus, to arrive at 440 ppm by midcentury—a plausibly achievable “safe” level in terms of its likely climate change consequences but only 60 ppm more than the current one—cumulative emissions should be kept to roughly 900 billion tons, or roughly 21 billion tons a year on average until 2050. This goal can be achieved by ending deforestation (on a net basis) and by cutting our current fossil-fuel-based emissions by one third.
‘Stabilizing climate requires near-zero emissions’
A new climate science paper calls for dramatic action
Avoiding climate catastrophe will probably require going to near-zero net emissions of greenhouse gases this century. That is the conclusion of a new paper in Geophysical Research Letters (subs. req’d) co-authored by one of my favorite climate scientists, Ken Caldeira, whose papers always merit attention. Here is the abstract:
Current international climate mitigation efforts aim to stabilize levels of greenhouse gases in the atmosphere. However, human-induced climate warming will continue for many centuries, even after atmospheric CO2 levels are stabilized. In this paper, we assess the CO2 emissions requirements for global temperature stabilization within the next several centuries, using an Earth system model of intermediate complexity. We show first that a single pulse of carbon released into the atmosphere increases globally averaged surface temperature by an amount that remains approximately constant for several centuries, even in the absence of additional emissions. We then show that to hold climate constant at a given global temperature requires near-zero future carbon emissions. Our results suggest that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures. As a consequence, any future anthropogenic emissions will commit the climate system to warming that is essentially irreversible on centennial timescales.
The fraction of CO2 remaining in the air, after emission by fossil fuel burning, declines rapidly at first, but 1/3 remains in the air after a century and 1/5 after a millennium (Atmos. Chem. Phys. 7, 2287-2312, 2007).