In most of the scenarios that talk about climate change, we are told about projections for 2050 or even 2100, time scales that are so far away that we have the illusion that the major risks will only be for “future generations“. And these scenarios evoke the possibility of a rise of 1, 2 or 4°C in several decades, a figure that should seem derisory when we are used to seeing temperatures vary by 10 or 20°C within the same day, by 15, 20 or even 30°C between winter and summer. In this context, how can we finally think seriously about climate risk?
Is the message getting through?
Before hoping for concrete actions, it is important to be aware of the seriousness of the upcoming risk. The heat wave of the summer of 2022 will have left its mark on people’s minds, yet when we look at the way the media has tended to talk about heat waves in recent years, we can legitimately wonder. O’Neill et al. (2022) examined the visual media coverage of the 2019 heat waves in France, Germany, the Netherlands, and the United Kingdom. As they explain, the vast majority of images used were associated with the idea of “fun in the sun,” with photographs of people having fun in the water, or by the water. And when the images actually depict the danger of this extreme heat, there is no one in the photos. This visual framing of heat waves is problematic, hiding vulnerable people.
But if we want to be fair and rigorous, we must admit that reality is complex, and talking about temperature alone is not enough. Sherwood & Huber (2010) have shown that in addition to temperature, humidity should be considered: a humid temperature of 35 degrees would be the acceptable upper limit, beyond which the human body can no longer cool itself by evaporating sweat from the body surface to maintain a stable core temperature. During the Chicago heat wave of 2015, which caused several hundred deaths, 29 degrees (only) were exceeded, over the course of a day, as Klinenberg (2022) recalls. Similarly, during the 2003 heat wave that killed tens of thousands of people in Europe, the 30 degree mark was not exceeded. Adding a few degrees is not adding “a little” discomfort. The function of well-being as a function of temperature is very far from being linear when we reach the extreme temperatures. Having temperatures of 5°C above the seasonal average in spring may delight the majority of the population, but in the height of summer, it can come dangerously close to life-threatening levels, as the heat wave in Pakistan in the summer of 2022 showed.
Linear or exponential evolution?
The main mistake in talking about climate change is to believe that it is only a “linear evolution” of temperature, which will translate into a “linear evolution” of risks. This is for example what can be observed in Figure 1, with on the left the evolution of the temperature observed in Chambéry, over 10 years, with a linear increase of the daily temperature, with a gain of 3.2°C over 10 years.
Figure 1: Average daily temperature in the suburbs of Chambéry, between 2012 and 2022 on the left, temperature distribution in 2012 and 2022 in the center, and comparison of the probabilities of exceeding a given temperature (source auteur).
On the left, a linear trend has been fitted to the observed mean temperature, each day. In the center, we observe the translation (to the right) of the temperature distribution over the year (if we assume that the temperature follows a normal distribution, as illustrated in several IPCC reports, for example IPCC (2022)). On the right hand side, we observe the evolution of the ratio between the probability of exceeding x°C in 2022, and the probability of exceeding x°C in 2012. There is thus five times more chance of exceeding 35°C in 2022 than in 2012. Note the (almost) exponential growth of this ratio, corresponding to the probability of having a heat wave (Charpentier (2022) returned to the difficulty of perceiving exponential growth).
Based on these data, we can estimate a gain of 3.2°C over 10 years, which is much higher than the orders of magnitude of temperature variations mentioned in most climate reports (starting with the IPCC synthesis). Indeed, these reports evoke a global warming of +1°C, or +4°C, compared to the pre-industrial period, under the angle of average global temperatures. However, climate change is far from being uniform in space, with some regions of the globe warming much more than others. And the warming scenarios are at the global level, or at the level of large regions like Europe or the Mediterranean basin. It is quite new to have evolutions at the scale of (small) metropolises. The distribution of temperatures can also change with a change in mean (the one we often talk about) but also, potentially, in variance, as reminded by Douville et al. (2021). In Figure 1, the variance has increased slightly over the last decade, which translates into more spreading, and thus more extremes.
To illustrate the non-linear consequences of linear temperature growth, we can mention the case of hurricanes. Reed et al (2020) showed that Hurricane Florence (which made landfall in North Carolina four years ago) generated up to 50% more rain and was 80 km (50 miles) larger in diameter due to ocean warming. Beyond debates about whether or not tropical storms are more numerous (the scientific community continues to make progress on this issue), we now know that the strongest storms are getting stronger: wind speeds increase by about eight meters per second per degree Celsius of warming. And since the cost of storms grows exponentially with wind speed, a linear increase in temperature mechanically translates into a cost of storms that grows exponentially fast with global warming.
The non-linearity of the dynamic systems that govern climate change is a component that should not be overlooked. For example, melting ice leads to a vicious circle of positive feedback, which only makes the problem worse. Cool ice is white and reflects some of the sun’s heat back into space. As the sea ice melts, the white ice turns into dark water, which absorbs more heat and reflects less. This causes the region to warm up even faster. On Greenland’s glaciers, the melting ice dirties the white glaciers, so they also melt faster. In Siberia and northern Canada, where the ground was once permafrostiii – “permanently frozen” – the frozen layer is no longer permanently frozen. And this permafrost contains enormous quantities of methane, produced by the decomposition of vegetation. Methane is a much more potent greenhouse gas than CO2, which will worsen the situation by causing even more warming. The same situation applies to forest fires: warmer temperatures dry out forests, and help create the ideal environment for larger and more frequent forest fires to occur. And this in turn leads to higher CO2 emissions directly from burning wood, further exacerbating climate change and contributing to more fires in a feedback loop.
In dynamic systems, a “tipping point” is when there is a critical threshold, in a hysteresis loop, beyond which the system rapidly changes state, very often irreversibly. In other words, close to this point, small perturbations can, due to the feedbacks we were talking about before, lead to changes of state with diverging equilibrium trajectories. Nordhaus and Boyer  highlighted some potential state changes in climate tipping elements: Rapid sea level rise caused by the collapse of the West Antarctic ice sheet (or other sources); changes in weather patterns such as the Indian summer monsoon or the West African monsoon; and the cessation of the Atlantic Meridional Overturning Circulation (AMOC, corresponding to what would be called “Gulf stream” in French). Other studies have pointed to other candidates, ranging from a collapse of Arctic summer sea ice to ecological regime shifts in the Amazon or Sahel, to a massive release of carbon from permafrost or seabed methane hydrates.
In many cases, climate change is not directly and exclusively the cause of disasters such as droughts or storms, but it is clearly making these events more intense, with increasingly severe economic consequences. CO2 and other greenhouse gases, largely from power plants, vehicles, buildings, industry and agriculture, trap heat in the atmosphere, warming the planet. In addition to the increase in temperature, global warming increases evaporation of surface water into the atmosphere, drying out areas that have received little rain. Warmer air increases the amount of water vapor the atmosphere can hold, and the thirstier atmosphere sucks moisture from the surface. This extra moisture is carried away by winds and eventually develops into storms, often thousands of miles away, that bring more rain. Atmospheric humidity has increased by 5% to 20% in general, compared to the period before the 1970s (which will lead to more deaths during heat waves, as we mentioned earlier). And water vapor is a greenhouse gas, which further amplifies warming. When water evaporates, it absorbs heat, and when it then falls as rain, and this heat is released into the atmosphere. This extra energy fuels storms, leading to more intense systems that can also be larger and last longer, with up to 30% more rain as a result of warming, as Kopp (2016) reminds us.
The fable of the frog and weak signals
We are thus in a complex dynamic system, where the causal variables seem to grow slowly, in an almost linear fashion. This is reminiscent of the fable of the frog. The fable of the frog is that of a scientific experiment. In the second half of the nineteenth century, William Sedgwick conducted experiments on nervous sensitivity, and he showed that if a frog was plunged (suddenly) into warm water, it escaped instantly, whereas if the temperature of the water increased very gradually, the frog, through habituation or numbness, remained inert, and eventually died. Although this experiment has been widely commented on and contradicted, it has ended up becoming a fable, implying that when a change is carried out in a sufficiently slow manner, it escapes the consciousness, and then does not arouse any reaction or opposition, unlike sudden and brutal changes.
Is there not an obvious parallel with what we are experiencing? If science tells us that this story is false for frogs, could we not apply it to humans, and accept the moral of the fable? Shouldn’t we see the other side of the coin of the tremendous adaptability of human beings? For we all have bad habits to which we have finally become accustomed, and which can cost us dearly in the long run. It often takes a major effort to recognize mistakes and change behaviors that have become normalized. Because the consequences of climate change are clear and alarming. If emissions are not quickly reduced, warming in this century will exceed that of the last half-million years. As in the case of the frog, the slow pace of change combined with our rapid adaptation, one might think that everything is normal. But it is not, and it is important to be aware of how we are collectively adapting to this new climate.
Collective Decision Making
Barry & Charpentier (2020) returned to the difficulty of collective decision-making. The first step is a collective awareness and acceptance of risk. Meyer & Kunreuther (2017) remind us that of the many possible consequences of climate change, sea level rise has long been the least controversial. Since the 1800s, sea levels have been rising steadily around the world, representing an obvious, clearly identified risk, but one that represents a subtle and misleading danger. For short-term risks, we know that people have difficulty seeing beyond one or two years (we will speak of myopia) and underestimate the probability that they themselves will suffer harm. Here, we are talking about a 15 or 30 year risk, a time horizon beyond the horizon of most mortgages, and even of some lives. Yet one would think that sea level rise is an easy risk to manage: we know it is coming, and we have the time and resources to deal with it preventively. And yet nothing is happening, collectively. Indeed, first of all, it is difficult for elected officials to have the wisdom to commit to large financial expenditures whose benefits will be realized long after they have finished their mandate (we will speak of the “myopia” effect). In addition, the uncertainty about the exact magnitude of sea-level rise creates a bias toward the status quo of doing nothing (the “inertia” effect). Finally, the fact that most cities are taking a similar wait-and-see approach is misinterpreted as evidence that officials in these other cities know what they are doing (the herd effect).
Thinking about “future generations”
Another difficulty is for whom these efforts are being made (or would be made). The situation has deteriorated so much in the last few decades that few of us expect to see it improve in our lifetime. Then comes that other fable, that of “future generations”. If we do not act for ourselves, we must do so, morally, for “future generations”. But thinking about “future generations” in ethical and moral terms is often complicated. Indeed, ethics seeks criteria for “just” actions, the obligations we have towards ourselves and others. However, “future generations” are others who do not exist, and one may wonder whether it makes sense to recognize rights to “human beings” who do not yet exist (and who we do not know if they will ever exist). From a legal or juridical point of view, it is by his existence (and his birth) that the human being obtains rights, and logically, there can be no obligations towards persons who do not exist. With this vision, there can only be damages and prejudices towards living persons, and not towards hypothetical “future generations”. Is it possible to conceive of a form of responsibility that extends to that distant future that is evoked when we speak of these “future generations”? The first Earth Summit, held in Stockholm in 1972, attempted to introduce a form of coherence into responsibility, with rights that would take into account this “trans-generational” dimension, as Gosseries (2004) reminds us. And to consider these “future generations” is also to conceive of ourselves collectively as a generation, which would have a form of collective responsibility, from one generation to another. The natural question that arises is whether I can be held responsible for the actions (and non-actions) of my generation?
This moral and ethical aspect is important, but it also raises major economic questions, since collective decision-making is often based on a cost-benefit analysis. Charpentier and Cherrier (2019) returned to the difficulty of assigning a monetary value to things that do not have one, and probably could not be exchanged on any market, such as human life. In the context of environmental damage, as Sen (2004) stated, “the very idea that I treat the prevention of an environmental damage just like buying a private good is itself quite absurd”. Specifically, Posner (2004) and Singer (2016) questioned the choice of discount rate, the actuarial approach was perhaps questionable when dealing with environmental goods. With a discount rate of 5%, the value of ten billion lives discounted over 500 years is the same as the value of about 50 lives today. Cynically, cost-benefit analysis reinforces our preference for the present, urging us to let the future take care of itself, even if the action we forgo today was a once-in-a-lifetime opportunity to save humanity.
Pandemic, climate change and science
This difficulty in thinking and acting collectively is reminiscent of the pandemic debates of the last few years, which could be linked to the denial of science in most developed countries. We have seen many decision-makers refuse to believe the recommendations of scientists, and continue to see the world with blinders on. We can think of the denial of the transmission of the virus by air, the non-taking into account of the so-called “Covid-long” situations, or the multiplication of post-Covid cardiovascular accidents. In the case of global warming, it is the refusal to take really effective (but often restrictive) measures by repeating fairy tales, with a technical progress that will come to save us one day. In the context of the pandemic, the idea that we would have to “live with it” ended up imposing itself collectively, and one can wonder if this is not also the case for climate change, even if the “tragedy of the commons” shows us the dangers of this approach. In Garrett Hardin’s fable, a group of villagers graze their cattle on the village common, which thus becomes overgrazed. Each villager knows that he or she should stop adding livestock to the herd because the common good cannot support more. But each individual also knows that if he adds one more cow to his herd, he will benefit greatly. And the common good will only marginally deteriorate. Each person is therefore motivated to continue to enlarge his own herd until the common good disappears, under the pressure of all the villagers.
Just as in this fable of villagers sharing a common land, a simple cost-benefit analysis (based on immediate losses and gains) of the consequences of climate change will lead to climate inaction in all countries. Here we find the argument we often hear: there is no point in decarbonizing as long as China does nothing. The reality of international trade should remind us that much of China’s carbon emissions are a response to our consumption patterns in Europe and North America. If thinking about “future generations” means imposing a form of collaboration in time, it is now important to think about collaboration in space. For from the point of view of climate change on earth, the CO2 released in Paris is interchangeable with the CO2 released in Beijing, Sydney, Cape Town or Montreal. Many have pointed out that the atmosphere is a “global commons,” such as Everard et al. (2013) or Bosselmann (2019). One consequence is that we are quickly faced with a particularly complicated form of the free rider problem, where we hope that future generations or other countries will make the necessary efforts, because we are content to see the cost associated with taking action to slow climate change. What if taking action could have benefits not only in the long term and far away, but also very concretely today? What if, as in Figure 2, we had the opportunity to create a truly better world?
Figure 2 : Joel Pett (author’s permission)
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