THREAD O'Connor is wrong. The EU has carefully considered WTO rules, as it likes to adhere to them. The rules allow introducing charges at the borders amounting to the equivalent of a domestic tax directly levied on certain products. https://www.stuff.co.nz/national/politics/124227077/trade-minister-damien-oconnor-wary-of-ad-hoc-carbon-tariffs-proposed-by-britain

Article XX b allows introduction of additional measures “necessary to protect human, animal or plant life or health”.
And Article XX g allows introduction of measures “necessary for the conservation of exhaustible natural resources”

So while WTO rules don't explicitly mention climate change, It could easily be argued that measures aiming at climate change mitigation seem to be in accordance with the WTO rules if interpreted with the spirit of these rules in mind.

finally, this TIME article on new WTO head shows she has quite different ideas on carbon charges than either @DamienOConnorMP or indeed Scott Morrison. https://time.com/5938816/ngozi-okonjo-iweala-wto-climate-change/