"With coal exports rising like that what effect is our carbon tax going to have?"
If the carbon ets wafpp accelerates the development of carbon capture and storage technologies then there is no issue for coal at all.
Or it could shore up the demand for LNG which we just happen be developing on a MASSIVE scale.
Or we could just sit back and wait for other countries to do the above and then we will eventually find that we have nothing at all to sell to the world.
Those with the most to lose have the most to gain.