While our responsibility for global warming is no longer denied but by an (unfortunately powerful) minority of individuals, the means to mobilize in order to tackle it are far from unanimously accepted, particularly when it comes to reducing the birth rate.
CO2 emissions = (CO2 / Energy) x (Energy / GDP) x (GDP / Population) x Population
where GDP represents the Gross Domestic Product. This relationship has undeniable qualities that we will examine later, but its simplicity suggests that it is an indisputable causal relationship, whereas it is only an identity. Indeed, after having deleted on the right hand side the terms Energy, GDP and Population, which appear simultaneously in the numerator and denominator, we see that we have simply written the identity CO2 = CO2. Subject to a minimum of coherence, a multitude of variants of this relationship can therefore be constructed. For example, the term Population can be replaced by "length of this note" or "number of Tweets of the American President". Terms can be added or removed without invalidating the veracity of the identity, as long as the numerator and denominator on the right side of the expression are touched simultaneously. Why then is Kaya's identity so successful?
Cogito, ergo polluo
Using Kaya's identity has a great advantage: it requires a minimum of coherence, which is not a luxury when it comes to public policies, environmental or not, where promising everything and it's opposite is the rule. First, as soon as the work of scientists, compiled by the IPCC, create a very strong presumption that human activities increase CO2 missions, the presence of the term Population as a positive factor (i. e. as the numerator) is essential, and it must also be put in the denominator to respect the arithmetic balance of the relationship. As a living species, humans emit greenhouse gases, but it is rather the whole of their production and transport activities (measured by GDP), i.e. energy consumption and the resulting emissions, that must be incriminated, which completes the list of suspects. In short, Kaya's identity makes the chain explicit: we exist, therefore we consume, therefore we produce, therefore we pollute. But, beware, the "therefore" (Descartes' "ergo") makes us move from an identity to a multi-causal relationship that negationists can easily dismantle.
The second advantage of the formul is the multiplicative nature. The four quantities on the right side of the identity are i) the carbon intensity of the energy needed for production and transport, measured by CO2 / Energy, ii) the energy intensity of the economy, measured by Energy / GDP, iii) GDP per capita, and iv) the population. Each of these magnitudes is affected upwards or downwards by specific public policies, and efforts on one are useless if nothing is done for the others. Thus, innovations that reduce carbon intensity by 10% (replacement of coal by renewables or nuclear power) will have no effect on carbon emissions if simultaneously GDP per capita increases by 10%.
It's the population, Stupid
The objective set for 2050 to achieve carbon neutrality, i.e. to emit less than what nature (assisted by capture and storage techniques) can absorb so that the atmospheric stock of CO2 no no longer increases or even decreases, is currently entirely dependent on very optimistic reductions in the first two factors: decarbonation of energy to reduce the CO2/Energy ratio, and increased energy efficiency to reduce the Energy/GDP ratio. No one in the political landscape would dare to publicly mention that the standard of living (GDP per capita) is being reduced, and, worse, that the population is being reduced. On the contrary, the world population is expected to increase from 8 billion people today to nearly 10 billion in 2050, about 25% more than today. As for GDP per capita,taking an average annual increase of 1.5%, this indicator of living standards should be about 60% higher in 30 years' time than it is today. So if we want to divide today's carbon emissions by 3 in 2050, the cumulative effort required for the two adjustment variables, carbon intensity and energy intensity, is a division by 6. 1The creative genius of engineers is immense, but this performance seems difficult to achieve in such a short time. By way of comparison, the emission intensity per unit of GDP has been reduced by one third globally and by half in Europe over the past 20 years. So, inevitably, the focus is on the main troublemaker, human population.
Family planning and environment
It is difficult to imagine what a long-term balance between demography and the environment will look like, and how it will be achieved. Recent history, in this case China's, shows that even an authoritarian regime has difficulty curbing population growth. From 1979 to 2015, the Chinese authorities penalized parents with more than one child and carried out sterilizations and forced abortions. After several easing measures, this one-child policy was replaced in 2015 by a policy setting the maximum number of children per family at two. Lately, the Chinese population has begun to decline. In democratic regimes, is it possible to reduce the population? India is trying to do this with the opening of information centres on contraception and an incentive sterilization policy, with the resulting abuses reported in Rohinton Mistry's novel "A fine balance". By interfering with the freedom to procreate, this kind of policy necessarily conflicts with the ethical values of democracies.
Returning to the sad demo-environmental arithmetic, by balancing births and deaths, the world population is currently growing by more than 200,000 people per day, with wide disparities between countries. This demographic pressure poses problems in all areas, particularly for water and land resources, and energy consumption. The question of the number of individuals that the planet Earth can decently accommodate will inevitably arise in a future that may not be so distant. The answers given by economics are not ethically satisfactory. The standard utilitarian approach leads to the 'repugnant conclusion' that everyone's well-being should be sacrificed to increase the population to the survival level. And if we invoke economic rationality, the solution is always the same: negative externalities must be taxed. So, in addition to the 'carbon tax', a 'fertility tax' must be introduced to force potential parents to internalize the environmental consequences of their decision to procreate.
At a time when world leaders at COP25 in Madrid are deciding on the future of humanity by bargaining their climate commitments, it is good to get back to basics. The climate disruption is due to the economic activities of an increasing world population. Humanity rightly aspires to a decent standard of living. To satisfy this legitimate need on a habitable planet, two things must be done: (i) decouple economic activity (measured by GDP) from greenhouse gas emissions, (ii) accelerate the demographic transition. History shows that the two are linked: an increase in the standard of living reduces the birth rate. It is therefore necessary to succeed in increasing the GDP per capita of the poorest people with low-carbon production methods.
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