Senator BIRMINGHAM (South Australia) (14:50): Mr President, I ask a supplementary question. I refer the minister to her statement yesterday to the Senate regarding carbon tax revenue that: The government updates its costings in the usual way in the budget and in budget updates, and that is the approach the government will be taking. I ask the minister: why did the government not update its estimates for the carbon price in 2015-16 when it handed down this year's budget but instead relied on estimates that were at least a year old? Senator Jacinta Collins: Mr President, I rise on a point of order. On one occasion there was a question that was very vaguely linked to the principal question, but on this occasion it is not a supplementary question. Senator Birmingham: Mr President, on the point of order—and I understand Senator Collins may not appreciate this, but I would have thought that Senator Wong would—the initial question referred to the BCA and to concerns about the artificial inflation of the carbon price. Senator Wong: Investor confidence. Senator Birmingham: The initial question—do you want me to quote it?—referred to 'concerns from the Business Council of Australia that the government may be about to artificially inflate its carbon tax through changes to international trading rules'. Such an action would have a direct impact on revenue, which is what the supplementary question is about. The two are very clearly related, Mr President. The PRESIDENT: Order! I am going to allow the question.