What are the costs if climate change increases the risk of extinction of plants and animals? What value can be placed on reducing the risk of extinction of the white rhinoceros or American pika? And do people consider these things valuable even if they will never see a white rhinoceros or a pika in person?

That value — the “existence value”— is one of the ecological costs being calculated by researchers at UC Davis and Fordham University in order to improve the models currently used to calculate climate change damages, what’s known as the social cost of carbon.