Regarding your question about who is responsible for the GHG emissions when coal is traded internationally, I'll share what I tell my students during our carbon trading simulation: «The carbon follows the money.»
If you're interested in how I run my carbon trading simulations and in the responses we get from students, you can see the paper at asa3.org/asa/PSCF/2009/PSCF6-09Heun.pdf.