Stabilizing French debt will require a massive and collective effort, according to Terra Nova.

To halt the spiral of public debt growing faster than national wealth and stabilize it at around 120-130% of gross domestic product (compared to 115,6% of GDP at the end of June), "100 to 120 billion euros in savings will be needed compared to a situation where spending increases at the same rate as national wealth. This is in addition to what will be needed to slow down certain expenditures that are growing faster than GDP, such as pensions and healthcare," Guillaume Hannezo, associate professor at the École Normale Supérieure and author of this note from the left-leaning think tank, told AFP.

This effort of 100 to 120 billion euros, comparable to estimates from the Court of Auditors or economic institutes, represents 3,5 to 4% of GDP.

It corresponds to the amount that the debt burden (interest payments) could reach in a few years if the entire 3.400 trillion euros of French debt were refinanced at the rate of 3,5% currently demanded by investors to lend money to France over 10 years.

Offsetting this amount through increases in tax revenue and savings on public spending would prevent interest payments from becoming a source of additional debt.

For an adjustment of this magnitude, "we are not mincing words" and "everyone will have to contribute," writes Mr. Hannezo, referring to the recovery efforts undertaken by the countries of Southern Europe (Italy, Greece, Spain and Portugal) around the year 2010.

He proposes two main levers: "reduce the flows saved (therefore useless) on public retirement spending" by preserving the lowest pensions and increase one of the moderate-rate taxes "paid by the largest number", VAT or CSG.

But we will not be able to "make these sacrifices acceptable without a very large sustained effort from the richest and at least a temporary effort from businesses", around 10 to 15 billion for each of these categories, with a targeted reduction of tax loopholes, he warns.

"Depending on their orientations, politicians try to make people believe that we can simply reduce the state's standard of living, with fewer civil servants, or work more, take back from the very rich or make companies pay: all of this can contribute, but none of these solutions is up to the task," this former economic advisor to François Mitterrand explained to AFP.

However, "this is an optimistic note," he added. With significant domestic savings, a diversified economy that remains attractive to foreign investment, and a strong state that knows how to collect taxes, France "will be able to achieve" this recovery.