According to World Gold Council each ounce of gold requires about 0.83 CO2e.   That is our initial standard to start our metrics but the truth is that it mainly accounts the fossil fuels required to do the extraction, It doesn't take in account the amount the biodiversity losses, deforestation, and water pollution.  We will have to develop new metrics to complete the impact evaluation that avoid the carbon tunnel and have more information for Nature as an Asset-Class.