I believe that the idea that China is obstructing a global carbon tax (among supporters of such a tax) mainly comes from racism and is not supported by the facts. However, people oppose global/national carbon taxes for a number of reasons unrelated to racism. I'm not sure why you are concerned with the authority to levy a carbon tax, since (1) such a tax would almost certainly be beneficial and (2) politicians already have essentially unlimited legal authority to raise taxes of any sort.