Due to its growing impact on societies, global warming has become central to public debate. If the majority of citizens have not read the reports of the Intergovernmental Panel on Climate Change (IPCC), the heat waves, the intensification of storms, the multiplication of extreme events are responsible for reminding them of the extent of climate change and the urgency of action.

Despite its documentation by the Intergovernmental Science and Policy Platform on Biodiversity and Ecosystem Services (Ipbes), the equivalent of the IPCC for biodiversity, the risks induced by the erosion of biodiversity remain less well perceived. Their links with climate change are underestimated, as if climate and biodiversity could be dealt with separately. This dichotomous view is misleading. We cannot act effectively in the face of global warming without taking care of biodiversity, and vice versa.

IPCC scientists have been explaining this to us since their first assessment report (1990). Climate is a stock issue. To stop global warming, it is not enough to reduce greenhouse gas emissions. Their stock in the atmosphere must be stabilized. In other words, achieving climate neutrality by reducing emissions – the flow entering the stock – down to the level of the outgoing flow, consisting of the absorption of CO2 by carbon sinks (forests and oceans) and the elimination of other greenhouse gases at end of life.

A quarter of greenhouse gas emissions come from “living carbon”, mainly due to specific agricultural emissions (unrelated to the use of fossil fuels) and tropical deforestation and other land uses that erode the continental carbon sink. Nor is there a path to neutrality without a profound transformation in the use of living resources ensuring the reflux of agricultural emissions and better protection of carbon sinks. This is the challenge of what can be called the agroclimatic transition.

One of the major difficulties of the transition is to carry out these two transformations, which refer to distinct economic mechanisms. For fossil carbon, it is necessary to introduce scarcity by reducing the use of coal, oil and natural gas to a bare minimum. For living carbon, it is necessary to reinvest in the diversity of ecosystems to reduce agricultural emissions and protect carbon sinks in a logic of bioeconomy.

Since the beginning of the industrial revolution, energy transitions have followed one another. They all consisted of adding new energy sources to a system initially based on the use of biomass. The result has been a massive increase in the energy used around the world.

The climate forces us to break with this logic. What lowers emissions is not adding decarbonized sources to the energy system. It’s to remove fossil sources: you have to switch from a logic of addition to a logic of subtraction.

Multiple instruments will have to be mobilized to bring about such a transformation. Among them, the taxation of fossil carbon has no equivalent. Whether it is obtained by taxation or by an allowance trading mechanism, this taxation increases the cost of using fossil energy without returning the resulting rents to its producers, as do soaring fuel prices. oil in the energy markets. On the demand side, it is a powerful stimulus to energy sobriety; on the supply side, it encourages people to turn away from carbon-based assets.

The main difficulty in taxing fossil carbon lies in controlling its distributive impacts. As the episode of the Yellow Vests in France showed, taxing fossil carbon without redistributing it to the most vulnerable poses more problems than it solves. Only a redistributive carbon tax will be socially accepted. Similarly, to expand carbon pricing on an international scale, it is necessary to proceed with a massive return of its product to the countries of the South.

Another pernicious form of fossil fuel subsidy: the free distribution of CO2 quotas in the European trading system, which hinders the emergence of a green industry, a lever for the competitiveness of tomorrow’s Europe.

Let’s imagine for a moment that the world had eradicated all use of fossil fuels by 2050. Would we automatically be climate neutral? Everything depends on what has been achieved on the second front of the transition, that of living carbon, the source of a quarter of global greenhouse gas emissions.

Fossil carbon taxation is of little use for the agroclimatic transition. Worse, it could even prove to be counterproductive: by using a CO2 price based on energy criteria, it would become profitable to transform the Amazonian forest (or the centuries-old oaks of the Tronçay forest) into short-rotation coppice to produce electricity. ‘energy ! The reason is simple. Agroclimatic transformation consists in finding ways of reinvesting in biological diversity, in other words the abundance of living things. But the price of CO2 does not reflect the value of this diversity. It is therefore necessary to use other instruments, which are more complex to implement.

Worldwide, the main anthropogenic footprint on the forest is tropical deforestation. Its major cause is the extension of land for cultivation and animal husbandry. This is why the key to stopping deforestation, in both dry and humid areas, lies in changing agricultural practices.

The impact of agricultural systems on the net balance of greenhouse gas emissions is not limited to deforestation. Depending on the techniques used, agricultural systems can themselves release carbon into the atmosphere (deep ploughing, drainage of wet soils, etc.) or, on the contrary, store it in living soils (conservation agriculture, agroforestry, etc.) . The former erode biodiversity by specializing farmers following industrial-type logic. The latter use the diversity of living organisms to intensify production and regenerate the natural environment.

These agro-ecological techniques also make it possible to better resist harsher climatic conditions while reducing methane and nitrous oxide emissions of agricultural origin. From an economic point of view, their promotion requires investment in research and development, the establishment of dedicated agricultural advisory networks and, above all, the promotion by farmers of the ecosystem services provided to society. This valuation does not occur spontaneously on the markets. It requires public intervention and dedicated funding.

The agroclimatic transition will finally have to integrate the question of the management of the oceans and marine biodiversity, which today are real blind spots in climate policies. Global warming and certain anthropogenic practices (overfishing, runoff of pollutants, etc.) are altering marine biodiversity, a crucial component of CO2 storage by the oceans. Protecting ocean sinks is essential to stabilizing future climates: it is estimated that the continental biosphere contains 4 times more carbon than the atmosphere. For the oceans, it’s 47 times.

The Climate Economics Chair of Paris Dauphine-PSL University is organising, in partnership with the Toulouse School of Economics and the National Museum of Natural History, the 24th Global Conference on Environmental Taxation), which will take place from September 6 to 8, 2023 and will be themed “Climate and Biodiversity: Tackling Global Footprints”.

*Christian de Perthuis, Professor of Economics, Founder of the “Climate Economics” Chair, Paris Dauphine University – PSL and Édouard Civel, Researcher at the Square Research Center and the Climate Economics Chair, Paris Dauphine University – PSL