Planetary Boundaries and Sustainability: Talk by Prof Noordin my former lecturer at UKM. Now in cycling ideas we must be good in creating words and terms. This time we talk about Planetary Boundary OR may be older word is threshold. What limit the environment can accept? At what level .GHG can sustain the world? At the moment some GHG are over the limit. That why some put this as one of the factors of the end of the world.