 This figure from the U.S. government in 2013 shows the estimates of the social cost of carbon, how much damage is caused to society by emitting a ton of CO2 to the atmosphere. It's done with various uncertain parameters and so they did a range of simulations of possible outcomes and so you get a distribution and the number of simulations to give a different number is shown here. If we start out with the blue one, which is the discount rate of 5%, which is the future doesn't matter much. So you're basically just concerned about now. Then what you end up with is a very low social cost of carbon, which might actually be zero, but probably is a little bit above zero. However, as you go through the green and to the red, which is essentially that the future matters a lot, what do you end up with is a much higher social cost of carbon. You estimate that when you emit carbon to the air, it costs society a whole lot. There's a very slight chance that it's low, but there's also a larger chance that it's actually really high and it could be very, very high. In sort of distribution, there's a best estimate it could be a little less, a little more, or a lot more is very common in these. But it's clear that when we emit carbon to the atmosphere, we are causing damage to society and allowing that carbon to be emitted to the atmosphere without paying for it is a sort of subsidy for fossil fuels.