Observing climate change issue especially CO2 emission problem, we tend to focus on power generation sector. In fact, 40 percent of world energy is consumed by means of electricity  and coal power plant is one of a major source that emits CO2 that accounts for over 40% of whole electricity consumption. However, while coal itself has same characteristics in terms of CO2 emissions based on its type: anthracitic, bituminous, lignite, and peat, coal-fired power plants are not identical. Generally, CO2 emissions from coal-fired power plants depend on efficiency that represents a proportion of input (coal) and output (electricity). For example, if the efficiency is 50%, then 50% of coal will be converted to electricity and the rest become loss mostly as heat. According to Ecofys , the energy efficiency of coal-fired production is different between countries. In United States, the average coal-fired power plant efficiency in 2008 was 36% which had not changed since 1990, while that of several OECD countries exceeded 40%.
Source: Data from Ecofys “International Comparison of fossil power efficiency and CO2 intensity” (2011)
Ecofys says this is because only 4.5% of coal power plant in 2005 was built after 1990 in United States. If United States improved its coal-fired power plant efficiency by 1%, it can reduce CO2 by more than 20 Mt-CO2, which is equal to almost half of amount of CO2 emission in Denmark . In theory, steam pressure and temperature in boiler are critical factors for improving coal-fired power plant efficiency. The most advanced coal power plant that is operated nowadays is called Ultra Super Critical (USC) and its efficiency is over 40% and now large plant companies such as Alstom, GE, Hitachi, Siemens, and Toshiba are tried to develop over 45% efficiency coal-fired power plant which is called Advanced Ultra Super Critical (A-USC). I think Replacing US coal power plants to those advanced coal power plants requires huge investment but the impact on CO2 emissions might not be ignored. Considering not only environmental perspective but also economy and energy security, I believe coal power plant has big potential in US to reduce CO2.
 International Energy Agency. (2011). CO2 EMISSIONS FROM FUEL COMBUSTION Highlights, 67.
 International Energy Agency. IEA Energy Statistics. 2012.3.3, http://www.iea.org/stats/balancetable.asp?COUNTRY_CODE=29
 Ecofys. (2011). International Comparison of fossil power efficiency and CO2 intensity.
 Coal CO2 emission factor: 2,410t-CO2/kg (Law Concerning the Promotion of the Measures to Cope with Global Warming, Japan)
 1% of coal consumption in US electric sector: 9.76Mt (U.S. Energy Information Administration / Annual Energy Review 2010, p216
 2,410t-CO2/kg * 9.76Mt / 1000 = 23.52Mt-CO2