also produced at regional level within countries, for instance for Orissa in India. As seen previously, calculation of the ecological debt implies various aspects related to political ecology. While calculating the amount of emissions, some scholars have disregard inequalities of emissions from the past whereas others have considered historical accountability. In addition, there is a connection between ecological issues and the economy due to the value natural resources have and the important role they play in benefiting our economy. In 2000, Neumayer calculated what he named the 'historical emissions debt', consisting on the difference in emissions of actual historical emissions (from a specific date in the past) and equal per-capita emissions (current emissions). Theoretically, it may be possible to put a money value on ecological debt by calculating the value of the environmental and social externalities associated with historic resource extraction and adding an estimated value for the share of global pollution problems borne by poor countries as the result of higher consumption levels in rich ones. This includes efforts to value the external costs associated with climate change. In 2015, Matthews proposed a method to calculate the ecological debt, by looking at the accumulated `carbon debts' for each country. The model uses historical estimates of national fossil fuel CO2 emissions and population and this since 1960. Furthermore, it runs a comparison between temperature changes each year by each country's emissions compared to a proportional temperature change of each country's share of the world population (this same year). This gives the accumulated credits and debts related to a larger range of emissions and the 'climate debts' obtained would be the difference between the actual temperature change (caused by each country) and their per-capita share of global temperature change. Other scholars have proposed a different approach, a `modified equal shares' approach, that would consider each country's basic needs and would weight each ones' share of emissions. However, this approach brings potential ethical and political difficulties to quantitatively defining what would thus be the equal shares. Key debates Although some recent emerging countries have participated in the increase of carbon emissions, the situation tend to stay uneven in-between developing and developed countries regarding who is affected the most versus who pollutes the most. Recent studies on ecological debt focus more on sub-topics as the notion of historical responsibility (whether or not a country is considered ethically responsible or accountable for carbon emissions