a blog about philosophy in public affairs

Do I make a difference? (2): A threshold phenomenon?

Previous post in this series:
(1) The exceedingly small but fully real effects of my greenhouse gas emissions

Many assume that individuals are not responsible for climate change and do not have any agency in tackling it. In this series of posts, I argue that this view is mistaken. The previous post concluded that individual emissions have an exceedingly small but fully real effect in that they increase the risk that vulnerable people suffer from climate change harms.

Extending this conclusion, in this post, I will address (and reject) the assumptions that individual emissions are neither necessary nor sufficient to cause climate change.

Walter Sinnott-Armstrong assumes that global warming will not occur unless lots of other people also expel greenhouse gases: an individual act is neither sufficient nor necessary to cause global warming. (1) These claims are two sides of the same coin: both are based on the characterisation of climate change as a threshold phenomenon. The claim that individual emissions are insufficient to produce harm assumes that emissions cause harm only after their accumulation exceeds a certain threshold. The claim that individual emissions are unnecessary to cause harm starts from the assumption that the accumulation of greenhouse gases already exceeds the threshold, and thus that climate change will occur anyway, whether or not an individual emits greenhouse gases.

I believe the characterisation of climate change as a threshold phenomenon is misleading – and that, therefore, Sinnott-Armstrongs conclusion that individual emitters cannot be held responsibility for causing climate change harms is misguided. I will argue this first by briefly showing that the threshold model has some implausible implications, and second by investigating different answers to the question as to where exactly the threshold is situated.


The greenhouse gas molecule that crosses the threshold

To me, the threshold model appears to imply that greenhouse gases emissions would be no problem at all, until, at some moment in time, there is one especially insidious greenhouse gas molecule that represents the last straw and all of a sudden causes climate change. The claim that individual emissions are neither sufficient nor necessary to cause climate change seems to imply that no emissions cause harm, but for the one greenhouse gas molecule crossing the threshold.

This clearly is not how climate change works. First, the threshold model treats earlier emissions (below the threshold) as insignificant, because they supposedly are insufficient to cause climate change. However, within the threshold model, it is clear that the harmful effects would not have obtained without all previous contributions. In real life climate change, historical emissions have already caused harm (see below). Second, once the threshold is exceeded, further emissions apparently do not matter either, supposedly because climate change happens anyway. This is misleading because further emissions exacerbate climate change and increase its harmful effects.

In my view, this quick argument already shows the inaccuracy of the threshold model: anthropogenic climate change is rather a gradual, additive process (although it might also include some abrupt transitions), exacerbated by each emission of greenhouse gases.


Setting the threshold

For the sake of the argument, suppose, however, for a moment that climate change is a threshold phenomenon. What would that threshold be?

The international community has accepted an increase in global temperatures of 2°C above pre-industrial levels as the threshold of dangerous interference with the climate system. (2) Does it make sense to put the threshold of harm at a level of greenhouse gas concentration in the atmosphere corresponding to this target? One problem here is that the global inaction and sustained annual growth in greenhouse gas emissions make it increasingly unlikely that humanity will succeed in curtailing the increase in global temperature below 2°C. From this perspective, each individual emission increases the likelihood that this threshold will be crossed, thus increasing the likelihood of dangerous climate change.

© 2015 AOSIS

© 2015 AOSIS

Moreover, the 2°C target is in fact arbitrary, politically agreed upon, and criticised by climate science (3) and ethics (4). For example, even a temperature increase below 2°C puts some unique and threatened systems (including Arctic sea ice and coral reefs) at risk. In addition, the Alliance of Small Island States has declared that global warming must be kept well below 1,5°C, since these states are especially vulnerable to and already experiencing the adversities of climate change. (5)

A related way of determining the threshold would refer to the critical thresholds (or tipping points) of the Earth system, beyond which abrupt or irreversible climatic changes will ensue. For example, by defrosting the permafrost, global warming might trigger the release of huge amounts of carbon, which will accelerate further warming and climate change. However, there is much remaining uncertainty and the Intergovernmental Panel on Climate Change has low confidence in the occurrence of abrupt changes in the 21st century. (6)

Most importantly, even below such tipping points or the 2°C threshold, global warming results in climate change harms. We currently observe an increase of global temperatures of about 0.85°C since 1880. This warming has already led to significant impacts on human life today. For example, the World Health Organisation has estimated that climate change was already responsible for 3% of diarrhoea, 3% of malaria and 3.8% of dengue fever deaths worldwide in 2004. The total mortality attributable to climate change was about 141,000 deaths in 2004, of which 85% were child deaths. (7) These numbers are rapidly increasing as climate change is continuing to exacerbate.

The only relevant threshold in climate change appears to be the point at which anthropogenic emissions started disrupting the balance between greenhouse gas sources and sinks. This threshold would be situated at the start of the Industrial Revolution, when the enormous expansion in the use of fossil fuels massively increased humanity’s impact on the Earth System. (8) If this is true, then those who maintain that climate change is a threshold case should accept that the only relevant threshold in climate change has already been exceeded more than 200 years ago.


Individual additions to climate change harms

I conclude that, although they may only have an exceedingly small effect, individual greenhouse gas emissions are sufficient to increase the risk that vulnerable people suffer from climate change harms. Each emission also necessarily exacerbates this process (except, possibly, when technologies to extract greenhouse gases from the atmosphere become practically available).

My point is not to deny that climate change is a problem of collective responsibility: climate change has become such a large problem because so many individual greenhouse gas emissions accumulated in the atmosphere. My point is rather that we should resist the temptation to dodge all individual responsibility by hiding behind some complicated model of collective responsibility. Individual emitters should accept responsibility for the exceedingly small but fully real effect their greenhouse gases have.

Nonetheless, the assumption that individual actions make no difference also permeates the discussion about the responsibilities of individuals in tackling climate change. This will be addressed in the following posts.


Go to the following posts in this series:
(3) Unilateral duties to reduce greenhouse gases or promotional duties?
(4) The agency of individuals and households



(1) Walter Sinnott-Armstrong, ‘It’s not my Fault: Global Warming and Individual Moral Obligations’, in W. Sinnott-Armstrong and R. Howarth (eds.), Perspectives on Climate Change: Science, Economics, Politics, Ethics (Amsterdam: Elsevier, 2005), pp. 285-307, at p. 289.

(2) See UNFCCC, Report of the Conference of the Parties on its Fifteenth Session, Held in Copenhagen from 7 to 19 December 2009 (2009). http://unfccc.int/resource/docs/2009/cop15/eng/11a01.pdf, paragraph 1.

(3) Samuel Randalls, ‘History of the 2°C climate target’, Wiley Interdisciplinary Reviews: Climate Change 1 (2010), pp. 598-605.

(4) Since the 2°C threshold is a politically agreed upon target, we should take into account the global context of large inequalities, as well as the inverse relation between responsibility and vulnerability. Whereas rich and powerful societies (who have polluted most) are disinclined to adopt a stringent target because this would require more costly actions from them, poor societies and people suffer most from climate change harms.

(5) AOSIS (2012), Alliance of Small Island States Leaders’ Declaration, 2012, http://aosis.org/wp-content/uploads/2012/10/2012-AOSIS-Leaders-Declaration.pdf. The AOSIS repeats this pledge for the climate negotiations in Paris in December 2015: http://aosis.org/small-islands-propose-below-1-5%CB%9Ac-global-goal-for-paris-agreement/.

(6) IPCC, Climate Change 2013: The Physical Science Basis. Contribution of Working Group 1 to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (New York: Cambridge University Press, 2013), http://www.climatechange2013.org/images/report/WG1AR5_ALL_FINAL.pdf, pp. 1114-19.

(7) WHO, Global Health Risks. Mortality and Burden of Disease Attributable to Selected Major Risks (Geneva: WHO, 2009). http://www.who.int/healthinfo/global_burden_disease/GlobalHealthRisks_report_full.pdf?ua=1, pp. 24, 50.

(8) Specifically referring to the increased use of fossil fuels and the accumulation of carbon dioxide in the atmosphere, Earth System scientists situate the onset of the Anthropocene – the current geological epoch in which human activity has become the main driver of global environmental change – in the early stages of the Industrial Revolution. See Paul Crutzen and Eugene Stoermer, ‘The “Anthropocene”’, IGBP Newsletter 41 (2000), pp. 17-18; and Will Steffen et al., ‘The Anthropocene: Are humans now overwhelming the great forces of nature?’ Ambio 36 (2007), pp. 614-621, at 616.

I am a Lecturer in Global Ethics at the Centre for the Study of Global Ethics (University of Birmingham). My current research mainly focuses on the ethics of climate change and the perspective of duty-bearers on issues of global justice. Broadly speaking, my research interests include global justice, human rights, environmental sustainability, cosmopolitanism and recognition theory.
For more info, please visit https://www.wouterpeeters.info


Do I make a difference? (1): The exceedingly small but fully real effects of my greenhouse gas emissions


(One of) Effective Altruism’s blind spot(s), or: why moral theory needs institutional theory


  1. Tom Parr

    Thanks for this second post, Wouter. Though I am very sympathetic to your position, I’m wondering whether you might be being a little unfair to one feature of the threshold model. Here goes:

    To begin: let’s suppose that 100 individuals share access to a lake and that (i) if individuals pollute the lake less than 100 units, then the lake’s water will still be usable, but (ii) if individuals pollute the lake 100 units or greater, then the lake’s water will be unusable for current and subsequent generations. I take this example to be similar to the case of climate change, as you described it above.

    Suppose now that I pollute the lake by 50 units. There is a sense in which this is not harmful by itself, since others might refuse to pollute at all. There is another sense which might seem problematic: in polluting the lake, I reduce others’ capacities permissibly to pollute the lake. Whereas it would have been permissible for each individual to pollute the lake with 0.8 units each, it no longer is. However, its not immediately clear that this counts as a harm and is thus impermissible. This is because I may be able to compensate the individuals whose capacities I have reduced. For example, if I pollute the lake by 50 units in order to create a technology from which everyone benefits, then it be permissible to do so, since I can compensate others using the proceeds of the pollution. The threshold model can explain this result, because it does not register my pollution as harmful and therefore impermissible. Its not clear that your model can generate the same plausible conclusions in this case.

    I’d be interested to hear what you make of this case, whether you think you’re position can explain our judgements about it, and what importance this might have for our rights and duties with respect to the threat of climate change.

    • Wouter Peeters

      Thanks, Tom, for your comment and your sympathy. Yours is a well-crafted example of a scenario in which the threshold model does work, and I fully agree with your conclusions. You are also right that my approach does not generate the conclusions you reach. However, the main reason for this is that I disagree with your assumption that the analogy applies to climate change.

      In order to make it applicable to climate change we would first and foremost have to make the adjustment that the lake remains usable, but each unit of pollution (starting from the very first) slightly increases the risk that users suffer or die from diarrhoea (this may be closer to real world pollution cases as well). That is, the lake has a precarious system of absorbing and putting to use its natural elements to produce drinkable water. Anthropogenic pollution (starting from the first unit) overloads and disrupts this system. Thus, I argue that polluting 50 units is harmful by itself, even 1 is, because it slightly increases the risk of suffering from water-borne diseases.

      A further problem with your analogy is that you assume that the lake is usable, and after the 100th unit of pollution, its water is no longer usable. To correspond to climate change, we should say that the water always remains usable, regardless the amount of pollution (the atmospheric capacity to absorb greenhouse gases is virtually infinite), and that it is the only lake we have. However, with each unit of pollution (starting from the very first) the risk increases that users suffer or die from diarrhoea. We already know that the risk is quite substantial and that people are already suffering from diarrhoea, but we keep polluting the lake (admittedly, partly because we, as individuals, do not have another choice). Moreover, we also know with great certainty that if we keep on polluting the lake, there will be other diseases that will cause suffering and death, and eventually, with very large amounts of pollution, the new chemical constitution of the lake will create a new life form that will ascend from the lake to exterminate us. (maybe I got a little carried away here).

  2. Wouter, I wonder if I could clarify here whether your objections to the threshold model lean more towards normative or empirical objections. In the second part of your post, you suggest that there may be some threshold at which we could say that our emissions have not caused climate change. If so, I am unsure I follow the objection to certain contributions being insufficient to cause climate change not tracking ‘how climate change works’.

    Consider a bin that will unbalance when it contains more than a certain amount of rubbish. It seems quite possible to say that the rubbish thrown into it before it reaches this tipping point does not cause it to unbalance and, indeed, that there is one piece of rubbish thrown into it that takes its contents beyond its capacity and is the ‘trigger cause’ for it unbalancing.

    It is compatible with this claim to say that we should not place all the blame on the person who throws into it the piece of rubbish that was the trigger cause and that other people exceeded some entitlement to bin space (or failed to offset/compensate others for doing so). But these normative claims would not challenge the empirical claim that the earlier contributions were insufficient to cause the effect. Nor would they even need they need to deny that we can deem insufficient contributions (qua insufficient contributions) morally unobjectionable. – e.g., “it does not matter that you did not cause the bin to fall; it matters that you took more than your fair share of its capacity”.

    Thus, I wonder if you could clarify: is the objection that something like the bin analogy is ‘not how climate change works’ or more that it does not properly model how we should think about the ethics? If the latter, could we level the objections without disputing the threshold model?

    • Wouter Peeters

      Thanks for you comments, Andrew, and sorry for the delayed response. I agree this might have been somewhat confusing. My argument in this and the previous post is actually to show that the normative conclusion that individuals cannot be held responsible for climate change because they do not make any difference is unjustified, because it is based on inadequate empirical assumptions about climate change. Considering climate change to be a threshold phenomenon is such an assumption that runs into some fundamental empirical objections.

      In the second part of the post I indeed try to reject different suggestions for a threshold in climate change, and I conclude that the only meaningful threshold for global warming is situated at the start of the Industrial Revolution, because the greenhouse gases emitted by burning fossil fuels started disrupting the precarious balance between sources and sinks of the natural greenhouse effect. Hence, even if we see anthropogenic climate change as a threshold effect, then the only emissions that were insufficient to cause climate change were those from natural sources (and even that is somewhat deceitful: natural greenhouse gases also cause global warming and climatic changes, but this has been kept in check by the absorptive capacity of sinks during the Holocene, and would not have become a problem for thousands of years if humans did not start dumping greenhouse gases in the atmosphere). The claim that an individual anthropogenic greenhouse gas emission is insufficient to cause climate change is thus unsupported, because each of them has an exceedingly small but fully real effect in that it increases the risk of climate change harms. Moreover, 200 years later, we already see the harmful effects of past emissions, and the question whether individual greenhouse gases, in the abstract, are insufficient or not has, in my view, become completely irrelevant.

      Similar to my critique to Tom’s lake-analogy above, I do agree with your conclusions in the case of the bin-example. However, I would deny that it is an analogy for climate change. Most importantly, climate change is not something that either happens or not (such as the bin tipping over), but a gradual process by which the risk of harm slightly increases with each addition of greenhouse gases (for example, a gradual increase in the bin’s bad smell?).

Leave a Reply

Your email address will not be published. Required fields are marked *

Powered by WordPress & Theme by Anders Norén