If you want to know what the financial health of a company is, you look at its balance sheet: assets on one side, liabilities on the other. A country's balance sheet would include assets such as roads and factories, along with human and social capital like education and entrepreneurship. Importantly, it would also include natural capital. On the other side, you'd see the depletion of natural resources as they're used up -- through mining, industry, forestry, agriculture. Rio+20 offers a unique chance to include `natural capital' in national accounts and move towards development that is more sustainable.