Although economic and technological progress should have strong influence on climate policy, they are often taken as granted in climate policy evaluation. Should some of them turn out differently, the effect and cost of climate policy could be widely off the mark. So, it would be advisable to consider adverse energy technology scenarios in designing climate policy. In this paper, we claim that South Korea is a good example, by showing that the climate policy evaluation is critically dependent on the assumption that the long term energy policy would carry out. In South Korea, energy policy is guided by “Energy Master Plan(EMP) "- a five-year national energy plan, and climate policy is manifested by a recently submitted “Intended Nationally Determined Contribution (INDC)” which proposes GHG emission reduction target by 37% below BAU emission level of 850MtCO2e by 2030. (In absolute terms, this is equivalent to limiting GHG emissions to 536MtCO2e excluding LULUCF). We show that (1) the emission pathway based on the reference energy consumption of the EMP would be compatible with INDC BAU (2) current energy policy is unlikely to achieve INDC target. (3) GHG emissions estimate without the reference case of the EMP would exceed INDC BAU by 18.9% in 2030 (4) Without the EMP, the carbon tax to meet the INDC target should be as high as 53,200 KRW/ton. It is 2.23 times higher than 25,200KRW/ton, the carbon tax to meet the INDC target with the EMP. And the GDP loss in 2030 due to carbon tax should be as high as 0.91% of BAU GDP, 3.6 times higher than 0.25%, the GDP loss in 2030 with the EMP.