That's exactly what I mean by "first order effect". We aren't actively and directly melting large quantities of ice. It's a second-order effect of increased at

That's exactly what I mean by "first order effect". We aren't actively and directly melting large quantities of ice. It's a second-order effect of increased atmospheric C02. One option is to allow it to vary but not as a first-order effect. Another option is to simply not let it vary to keep the model simple.