The key to analysing natural and societal interactions as economical relations lies in the concept of ecological debt, that is portraying society's debt to nature in financial terms. Of course when one speaks of society's financial debt to nature can only speak using a large conventional generalities and approximations.

Society constantly harms the environment and thus is always falling more into debt to nature. If one begins our calculations from the point where nature can completely renew herself, then any change in this state, generally caused by economic growth, could be considered environmental debt. If the environmental conditions improves under the influence of environmental protection measures, then this could be considered a reduction of environmental debt, the repayment of some part of it. It is very difficult to measure absolute size of the ecological debt economically. However, just as one analyses a foreign national debt and its correlation to a national income not by measuring the absolute size of the debt, but, rather, the rate of its annual change and the interest accumulated, so it is with environmental debt; the financial value of a debt accumulated over a long period seems to exceed the national income of a country, thus it is more accurate to analyse the debt's annual increase or decrease.

If society can decide whether or not to pay part of its environmental debt in a given year, then it should pay at least the interest on this debt. From my point of view, it is the interest on the environmental debt - the consequences of the environmental pollution, that is most often overlooked. Economics, functioning in polluted environment, suffer worse then those existing in favourable ecological conditions. Thus, the worse the environmental situation, i.e. the higher ecological debt, the higher interest on it.

In any given year an economy pays interest on the ecological debt, it accumulated in the course of previous years and, moreover the absolute size of this debt increases if one considers the deterioration of environmental conditions in this year in comparison those of past years. But if environmental measures improve the environmental conditions taken during the course of a given year, then the interest on the environment debt remains the same as in the previous case, but the absolute size of ecological debt decreases and this would be reflected in the following year by the payment of less interest - economic losses - owing to improving environmental conditions.

In foreign national debt analysis we discover, that reducing debt (through a positive import-export balance) reduces the size of a national income, but increasing the debt (through a negative balance) raises it, i.e. the payment of part of a foreign national debt reduces the size of a national income - expenditures for consumption and accumulation. There is the same situation with ecological debt, the only difference is that in the case of national debt grows, a national income increases at the expense of other countries, while ecological debt grows at the expense of nature.

Given such a situation where we hold promissory notes to nature firstly, that ecological debt grows excessively and results in either ecological catastrophe or economic catastrophe, owing to excessively high interest on this ecological debt. Second, if we succeed in stabilising the total value of the ecological debt at a certain ecologically safe level, then total repayment of the debt becomes less immediately necessary. It is expedient to the ecological debt when the cost of paying off the debt are lower than the gains gotten by reducing the interest on it, i.e. when environmental protection measures, aimed at repaying the debt are less expensive, than the national economic losses prevented by them.

Even if it is possible and expedient in certain situations to vary the repayment of ecological debt, one still can not avoid paying interest upon it, because the collection of interest occurs automatically - whatever environmental protection policies society introduces, economic losses of environmental pollution would nonetheless take place, and this is exactly the payment of interest on the ecological debt. The peculiar analogue of such process of economic interaction between society and nature manifests itself in situations, when interest is added to one's account constantly and without anyone's request or consent.

Up until now we have spoken only about one type of interest on ecological debt - about profits, which were reduced because of environmental pollution. However, ecological losses also figure into national income - for we must spend money to compensate for environmental distraction. In other words, such expenditures are a form of consumption, for example we must spend part of our national income on the treatment of diseases, which result from poor environmental conditions.

Representing the interactions between society and nature in terms of ecological debt allows us to use general methodological principles of financing and credit management in the sphere of ecological economic relations.

So we have discussed:

1. losses due to pollution, which occurred in environment during previous periods due to last periods (as we have named them above - interest on the ecological debt);
2. future losses due to pollution, which was produced in the present period and was not render harmless during this period (the increase of the ecological debt).

Let us cider a concrete example. A company, located by a polluted reservoir, spends considerable money during its first year to purify its environment and thus reduces its ecological debt. The second year, of course, a large profit was gained, because the reservoir was already clean and resources did not need to be taken away from production in order to purify it thus the interest on the ecological debt was decreased.

Obviously it is not wise to judge production efficiency during first and second years by looking at profits along. Profits would became substantially comparable - if the cost of environmental restoration were added to the profit of the first year, because the production of the first year repaid environmental debt of past generations.

An analogous situation occurs on the macrolevel. An economy, which suffers because of environmental pollution, pays interest on other's debts; these losses don't characterise production in the given time period and should not be taken into consideration when estimating the economic efficiency of the given period. It seems to me that the best way to do this is to add the interest and the repayment of other's debts to traditionally calculated national income.

But if the ecological debt increases then we should deduct its size from reckoning the traditionally obtained national income. Such modification of national income becomes understandable, when one considers operations, which adds the losses due to past ecological destruction, while subtracting the losses, perpetrated in the given period for future generations.

The subtraction of future losses from the national income can be understood as financial discharge of our debt to future generations and could be considered as appropriate payment to the nature amortisation fund.

In the following years economics will conduct environmental protection measures, which improve the environment condition, i.e. pays back ecological debt and by this carry the losses (except for the payment of the interest on ecological debts, incurred by past generations), which will be compensated by the nature amortisation fund. This means, that the actual profit of this period is equal to national income plus repayment of smaller profits due to financial expenditures for environmental protection measures, at the expense of the nature amortisation fund, minus the losses of future generations caused by ecological destruction during the given period (i.e. payments to the fund of the given period).

Thus, the addition to the national income of losses, which were caused by ecological destruction explains where the resources deducted from the national income during the last period as damaged losses go. Such dynamic process of payment and collection of ecological debts on macroeconomic level (and in intergenerational relationships reaffirms the principle - Polluter Pays.

In that way, in the version of the conception that I suggest, the new parameters brought into economic analysis to reflect sustainability of development are: ecological debt and ecologically adjusted economic macroindicies.

Practical realisation of this approach demands a continuation of work in the field of estimating economic losses, caused by ecological destruction and in particular, economic damage, caused by environment pollution - work, which has been going on in our country during the last two decades.

Active use of the concept of ecological debt allows to develop an economic view on the problem of sustainable development. The word sustainable in the term sustainable development carries the double load. On one hand it refers to the kind of economic development, which allows a balanced and sustainable environmental situation, and on the other, it refers to sustainable, permanent economic growth.

Increase of ecological debt in the course of the certain period of time is evidence of worsening environmental conditions. In connection with this in terms of economic analysis in order to achieve sustainable development we must not allow any increase of the ecological debt during the period in consideration.

The stabilising (or more precisely, the reduction of the absolute value) of the ecological debt together with permanent economic growth characterises the sustainable development path.

We can evaluate the criteria of sustainable development by using ecologically adjusted macroindicies, such as (GNP-ED), where ED is ecological debt formed in the course of a year. If the size of such an ecologically adjusted GNP is characterised by sustainable, permanent growth, then it is possible to label such development ecologically sustainable development.

Our calculations in multiindustrial models allow us to demonstrate in numerical terms the necessity of transition to the a fore-mentioned ecologically adjusted macroindicies; this is especially important in case society turns to the task of adopting the trajectory of sustainable development.

Earlier, while calculating models we chose traditional method for economic analysis of comparing of versions of environmental protection activities by their economic efficiency, i.e. comparing the cost to the results of each and every environmental protection program. In this way our task was reduced to the discovery of the maximum allowable level for various branches of industry. Such analysis of environment protection plans serves to determine rational scales for environmental protection activities from the point of view of its traditionally interpreted economic efficiency; and it leads us away from choosing a version, which corresponds to the sustainable conditions of the environment. The multy-industrial traditional efficiency analysis scheme can be expedient only if we have several versions, each of which provides for sustainable environment conditions.

In the search for the proper path to achieve the sustainable development model the question about admissibility of obtained summary values of a environmental damage, i.e. how they correspond to the sustainable environmental conditions, is very important. In fact, this is the question for the criteria of environment quality.

As an example of sustainable (admissible) environment conditions the state of the environment in 1965 was considered. Annual economic damage, made in that period, could be considered not damaging to the sustainable environment conditions.

From the point of view of achieving a sustainable environmental state the admissible version of economic development and environmental protection activities is the version, which differs from the traditional criterion of optimality, which was indicated above.

Ecologically adjusted value the GNP, i.e. value GNP, which could be disposed by given generation, is equal to the GNP - D, where D is damage made in the course of a year, here is considered as increase of ecological debt. In the one of versions it (GNP - D) reaches its greatest value in compare with other versions.

This version combines two sides of sustainable development: sustainable environmental conditions and sustainable, permanent economic growth (provided by a set trajectory of change of value of the final product).

According to our model, ecologically adjusted indices of GNP turn out to be 3-15% less, than the traditionally calculated ones, depending on the particular scenario of development at the end of forecast period. When we base our chosen strategies of economic development on non-ecologically adjusted economic indices, we disregard losses for the future generations and groundlessly give this part of the GNP to the present generation.

If the interests of future generations don't be taken into account, then the present generation could choose programs only according to economic efficiency. To overcome such a historically destructive point of view and environmentally egotistical opinion of each generation and to pass on the concept of sustainable development, it is necessary to reconstruct the methodology of economic analysis making the index of ecological debt as a basic criterion.

This paper reflects fundamental economic thesis's of the Conception of the transition to sustainable development and the author's interpretation about this development. It is clear, that the suggested principles to reconstruct economic analysis methodology could not be realised immediately. Besides, each thesis demands detailed studying.

In conclusion I would like to list fundamental structural elements of this concept, which simultaneously introduce both the program itself and the details initialled in its practical realisation.