Hi,
I agree with Chris that ABCD is utility cost, but it is still obscure for me that why you consider ABCD as elasticity cost that TIMES report as ELASTCOST. Consumers surplus is the cumulative opportunity gain of all customers who purchase the commodity at a lower price than what would they have willing to pay and similarly producer surplus is cumulative opportunity gain of all producers who sell the commodity at a higher price than they would have willing to sell. These area are AP1X and AP1F for the baseline. clearly in the documentation part 1 formula 6-6 it indicates that TIMES want to find the equilibrium by maximizing the surplus (surplus would be maximize at the intersection of supply and demand curves). Therefore, the cost of loss of welfare (surplus) would be ABEF.
As you explained ∆(surplus) = ∆(utility) – ∆(supply costs), it is generally true. But when we shift out supply curve, then we have the whole new equilibrium and this is not true anymore. Imagine if we did not shift the baseline supply curve then with reducing our demand to Q2 this formula would be true and we call ∆(surplus) deadweight loss here (ABR). But, if we shift supply curve, then our consumer surplus will be reduced by ABP1P2 and producer surplus will be reduced by AMEF-BMP1P2 , therefore the total surplus loss would be AMEF-BMP1P2+ABP1P2=ABEF.
I was very confused about this issue for a long time as many of TIMES papers and people mixed willingness to pay with surplus and I hope we can come to an agreement about this.