2011 – Chuluun Togtokh criticized the HDI in an article published in "Nature", calling for a revised HDI, writing that "The revised index should include each nation's per capita carbon emissions, and so become a Human Sustainable Development Index (HSDI)." Bravo (2014) provided details of how the HSDI was computed and proposed an amended HSDI by including the proportion of forested area in each country. He argued that this proposed indicator "represents an important measure of the capacity of the natural system to provide fundamental ecological services."