This thesis seeks to illustrate and examine the role of knowledge and discursive practices in global climate governance. The development of two policy concepts is analyzed via a discursive-institutionalist perspective: the ‘pledge and review’ mechanism adopted by the Paris Agreement and the ‘carbon budget’ who failed to be institutionalized into the UN climate regime. The activities of epistemic communities and the discourses on the two policy ideas by key policy actors are analyzed to gain insights on the policy dynamics. The research delivered several key findings: firstly, there are abundant qualified epistemic communities inputs for both policy ideas. Secondly, the success of pledge and review over carbon budget could be partially attributed to three factors: (1) the pragmatism discourse, (2) the dominant ecomodernist framing prevailed in Paris and (3) the assimilation of the carbon budget concept into the two degree discourse. Lastly, the concept of carbon budget, being excluded in UNFCCC, still has concurrent implications to climate governance: on one hand it gains traction outside the formal UN process and provokes non-state action like divestment; on the other hand it leads to legitimacy challenges of Paris agreement, displayed in the recent discourse by Donald Trump on the fairness of the agreement.