Hope for the best, prepare for the worst. In a short sentence, the Minister for Ecological Transition, Christophe Béchu, has shaken up the way of conceiving the plans for adaptation to climate change (PNACC) established for ten years by his ministry. The Minister, who was speaking at a conference on this topic organized by France Strategy and the Institute of Economics for Climate (I4CE), announced that he now wanted to take into account in the national adaptation strategy two hypotheses warming: an “optimistic” of a warming of 2°C on average in France but also a more pessimistic one. “When we see the recent projections of the IPCC, when we read the studies, we realize that to think that we are going to stay on a trajectory at +2°C when there are hypotheses where we are at + 4° C, this requires that we model this trajectory and that we have two scenarios in our adaptation strategy”, he explained.
It is not a question of dropping the Paris Agreement, which should make it possible to contain global warming below the 2°C mark, but of taking into account a possible overrun of this limit, and its consequences. “Calibrating this standard on a warming of 4°C means ending the taboo on global warming in France, and ensuring that the country is properly protected”, deciphers Ronan Dantec, environmental senator and vice-president of the sustainable development committee in the Senate. Since the period 1900-1930 the average temperature in France has increased by 1.7°C when this figure reaches 1.2°C on a global scale. An acceleration of global warming faster than elsewhere due to the geographical position of France, and which now makes the worst projections more plausible.
Review the maximum sea level
“Taking into account ‘optimistic’ and ‘pessimistic’ scenarios, and a very good thing to measure the impact of global warming on the scale of the different sectors of activity and territories”, underlines Vivian Dépoues, head of the adaptation project at the within I4CE. Until now, the various PNACCs (2011 and 2018) were not based on any particular scenario, and had no binding effect on public policies. The revision of this plan this year will therefore be an opportunity to concretely define the various risk thresholds for which France will have to prepare.
And these risks are multiple: unprecedented heat waves, longer drought, rising sea levels… “A France at +4°C will be very different from the one we know today, because the impacts will be numerous”, summarizes François Gemenne, co-rapporteur of the IPCC. Between 2 and 4°C, for example, mortality is likely to increase very sharply. “We estimate at 30,000 deaths per year the number of deaths in Europe due to heat waves in a warmed mode of 1.5°C, with +4°C in 2100 this figure could be three times higher”, warns Goneri Le Cozannet, co-author of the latest IPCC report and researcher at the Bureau of Geological and Mining Research (BRGM).
The researcher has also studied the risks of marine flooding linked to climate change, and here again recent observations show the extent of the work to be done for adaptation. “In the latest version of the adaptation plan, the maximum sea level rise in 2100 was estimated at 60cm, an estimate that leaves only a small margin of safety in a scenario of +2°C warming, and which would be exceeded beyond that”, explains Goneri Le Cozannet.
What acceptable risk?
What will be the necessary adaptation gap between the optimistic and pessimistic projections? Depending on the degree of warming, adaptation measures will have to be reinforced… Up to a certain level. “In the second scenario, the effectiveness of certain actions is likely to decrease sharply”, underlines the BRGM researcher. Thus for coastal protection, a “moderate” warming of 2°C leaves the possibility of natural adaptation, such as the restoration of coastal ecosystems of dunes or marshes. But beyond this limit certain modes of action will no longer be valid: “It is obvious that the higher the sea level rises, the more difficult it will be not to have recourse to the construction of dykes to protect oneself”.
Last June, the Institute of Economics for the Climate established eighteen essential measures to “catch up with accumulated delays” in adaptation. The whole had been calculated at an additional 2.3 billion euros per year. Scaling up adaptation to target a much warmer climate could therefore also see this cost increase. “The whole question will be how we want to adapt, and what solutions will be chosen, with different amounts each time,” warns Vivian Dépoues.
What will be the acceptable level of risk? Others have already chosen to include in their regulations adaptation plans based on maximum risk scenarios. Like London, where a barrier on the Thames has been installed to prevent the city from flooding, taking into account the worst projections of warming and rising water levels. With the hope that the worst never happens.