Lee Elder you stated:
We have been careful to state that it is only an estimate, and that there are both known and unknown factors that would alter the estimate.
Please, point to where you talked about the unknown factors for this estimate. I can see small sections in your report where you speak of some limitations but these are fleeting thoughts at best and does not go in depth with what they are or how you attempted to overcome those unknown factors.
Even two of the three studies that you make references too, in their conclusions they go into deep discussion of what the limitations are.
You also have said twice now for those that disagree with your methodology to go do our own estimate. I will contend with you on this again. No one who disagrees with how you came to that methodology has claimed to make an estimate nor have they claimed to put this in a research article, which you yourself calls the article. You have claimed that you have presented this estimate to a conference also you have said that you have a leading expert in this field who has helped to come up with this estimate.
So the pressure is on you to defend your numbers. Scientists don't submit articles to the peer reviewed journals, and when someone disagrees with them, they say well go off and do your own study and prove me wrong. It is up to the person who has presented the article to prove their facts. If you think you have proven your estimate by use of facts then you should be able to defend them legitimately.