East Side Mario's Parmeasan Cheese

What a level of unsustainable debt?? A

A high public debt can become "unbearable" for at least three reasons:

A - a problem of economic sustainability, if its value becomes such they pose no longer possible to pay interest
B - a problem of sustainability policy, if the amount is too high compared to public assets: in the latter case a generation receiving a high debt and assets limited public could decide to stop paying a debt accumulated by previous generations
C-a problem of economic efficiency The level of debt could slow the economy

At what points levels are "unsustainable" on each of these three criteria?

A-level sustainable economically depend mainly on the amount of interest payable, ie it will depend on the level of debt, but also the level of interest rates. U

country which has 200% of its GDP in debt with rates of 1.5% (for Japan) will have the same charge to pay a country who will be 80% of its GDP in debt with a rate of 4 % (for France). This explains how Japan can support a debt problem without significantly higher (at least as long as interest rates remain low) than is, for example, that of Greece.

Taking an assumed rate of 4%, and if one considers the level "unbearable" will be a drain of only 10% of GDP for debt, the level of debt "ceiling" is situated at about 250 % of GDP. It is still far ...

It is difficult to define what level of aspiration "unbearable" for a country.
Note however that the war damage inflicted on Germany in the 20s, do represented only 3% of GDP (4-7% according to other studies) - which represents a debt of 80% of GDP , ie the current level French ...

B - As stated a previous post you can calculate a "net public assets (value of public property - public debt). He is currently negative. At what level this "passive" Will it be too loud?

Hard to say. It would take to define what level of inequity between generations the social contract can be broken. And before that calculate a balance sheet thinner than the previous post, doing difference:

• performance "social economy" of public assets (knowledge, buildings, works of art) - that is, estimating the value which is taken (by adding the rent saved, the pleasure to watch table, the gain in wages for the education ,...).
  
• the cost of debt (easier to calculate)

This balance is difficult to calculate. However, what is easier to estimate is the evolution from one year to another, for example, during 2009:

• net new assets (ie, the value of jobs created less the value of those missing ) can be considered close to zero. Thus, young people were trained, but the number of people retiring now are stronger than those who finish their studies, "human capital" has not progressed
• increasing the debt was real
  

The total balance deteriorated 123 billion, an annual cost of 5 billion (0.25% of GDP) with a rate interest at 4%.

One can also estimate an "upper bound" to unsustainable levels as follows:

• assume that the current level of debt represents net assets equal to more than zero (by adding to the negative assessment cited above the value of intangible assets)

• assume a level of 'unacceptable' unfairness is the annual cost of 3% imposed on Germany in 1920 and has been a major cause of social crisis, and monetary policies that led to Nazism

Under these conditions, the level of debt that would make France would be on the brink of 160% of GDP: 80% (current level) + 80% (the level corresponding to a puncture of 3% per year without consideration for the generation who would pay).

C - The negative effects of debt on the economy can be separated into three categories: i
- foreclosure effects (public debt consumes all the available funding and stifling private sector)
ii - effects known as "Ricardian" businesses and citizens expect more taxes or fewer services tomorrow, and react to higher debt by reducing their consumption
iii - incentive effects: the puncture performed each year to pay interest on debt that citizens receive less service than they contribute in business (a part of their business is taxed to pay interest on the debt), which reduces their incentive to increase their activity

can estimate the breaking point for point iii with calculations similar to those of B. There are also some studies the points i and ii (one which I forgot the reference, the IMF or World Bank), but none can achieve precise quantification of the intolerable level.