Commercial coal has a carbon content of at least 70%. Coal with a heating value of 6.67 kWh per kilogram as quoted above has a carbon content of roughly 80%, which is

, where 1 mol equals to N_A (Avogadro Number) atoms.

Carbon combines with oxygen in the atmosphere during combustion, producing carbon dioxide, with an atomic weight of (12 + 16 × 2 = 44 kg/kmol). The CO₂ released to air for each kilogram of incinerated coal is therefore

.

This can be used to calculate an emission factor for CO₂ from the use of coal power. Since the useful energy output of coal is about 30% of the 6.67 kWh/kg(coal), the burning of 1 kg of coal produces about 2 kWh of electrical energy. Since 1 kg coal emits 2.93 kg CO₂, the direct CO₂ emissions from coal power are 1.47 kg/kWh, or about 0.407 kg/MJ.

The U.S. Energy Information Agency's 1999 report on CO₂ emissions for energy generation, quotes a lower emission factor of 0.963 kg CO₂/kWh for coal power. The same source gives a factor for oil power in the U.S. of 0.881 kg CO₂/kWh, while natural gas has 0.569 kg CO₂/kWh. Estimates for specific emission from nuclear power, hydro, and wind energy vary, but are about 100 times lower.

The energy density of coal, i.e. its heating value, is roughly 24 megajoules per kilogram.

The energy density of coal can also be expressed in kilowatt-hours, the units that electricity is most commonly sold in, per units of mass to estimate how much coal is required to power electrical appliances. One kilowatt-hour is 3.6 MJ, so the energy density of coal is 6.67 kW·h/kg. The typical thermodynamic efficiency of coal power plants is about 30%, so of the 6.67 kW·h of energy per kilogram of coal, 30% of that—2.0 kW·h/kg—can successfully be turned into electricity; the rest is waste heat. So coal power plants obtain approximately 2.0 kW·h per kilogram of burned coal.

As an example, running one 100-watt lightbulb for one year requires 876 kW·h (100 W × 24 h/day × 365 day/year = 876000 W·h = 876 kW·h). Converting this power usage into physical coal consumption:

It takes 325 kg (714 lb) of coal to power a 100 W lightbulb for one year. One should also take into account transmission and distribution losses caused by resistance and heating in the power lines, which is in the order of 5–10%, depending on distance from the power station and other factors.

Clean coal technology is an umbrella term used to describe technologies being developed that aim to reduce the environmental impact of coal energy generation. These include chemically washing minerals and impurities from the coal, gasification, treating the flue gases with steam to remove sulfur dioxide, carbon capture and storage technologies to capture the carbon dioxide from the flue gas and dewatering lower rank coals (brown coals) to improve the calorific value, and thus the efficiency of the conversion into electricity.

Clean coal technology usually addresses atmospheric problems resulting from burning coal. Historically, the primary focus was on sulfur dioxide and particulates, since it is the most important gas in the causation of acid rain. More recent focus has been on carbon dioxide (due to its impact on global warming) as well as other pollutants. Concerns exist regarding the economic viability of these technologies and the timeframe of delivery, potentially high hidden economic costs in terms of social and environmental damage, and the costs and viability of disposing of removed carbon and other toxic matter.

Coal, which is primarily used for the generation of electricity, is the second largest domestic contributor to carbon dioxide emissions in the USA. The public has become more concerned about global warming which has led to new legislation. The coal industry has responded by running advertising touting clean coal in an effort to counter negative perceptions, as well as by putting more than $50 billion towards the development and deployment of clean coal technologies, including carbon capture and storage. The expenditure has been unsuccessful to date in that there is not a single commercial scale coal fired power station in the US that captures and stores more than token amounts of CO2.

The world's first "clean coal" power plant went on-line in September 2008 in Spremberg, Germany. The plant is state-owned and has been built by the Swedish firm Vattenfall. The plant is state owned because of the high costs of this technology, since private investors are only willing to invest in other sources such as nuclear, solar and wind. The facility captures CO2 and acid rain producing sulfides, separates them, and compresses the CO2 into a liquid state. Plans are to inject the CO2 into depleted natural gas fields or other geological formations. This technology is considered not to be a final solution for CO2 reduction in the atmosphere, but provides an achievable solution in the near term while more desirable alternative solutions to power generation can be made economically practical.

According to the United Nations Intergovernmental Panel on Climate Change, the burning of coal, a fossil fuel, is a major contributor to climate change and global warming. As 25.5% of the world's electrical generation in 2004 was from coal-fired generation, reaching the carbon dioxide reduction targets of the Kyoto Protocol will require modifications to how coal is utilized.

Some in the coal industry and the U.S. Department of Energy refer to carbon capture and sequestration (CCS) as the latest in "clean coal" power plant technologies. The "clean coal" terminology is generally not endorsed by professionals in CCS, and is actively opposed by environmental organizations that favor CCS. CCS is a means to capture carbon dioxide from any source, compress it to a dense liquid-like state, and inject and permanently store it underground. Currently, there are more than 80 carbon capture and sequestration projects underway in the United States. All components of CCS technology have been used for decades in conjunction with enhanced oil recovery and other applications; commercial-scale CCS is currently being tested in the U.S. and other countries. Proposed CCS sites are subjected to extensive investigation and monitoring to avoid potential hazards, which could include leakage of sequestered CO2 to the atmosphere, induced geological instability, or contamination of aquifers used for drinking water supplies.

Supporters of clean coal use the Great Plains Synfuels plant to support the technical feasibility of carbon dioxide sequestration. Carbon dioxide from the coal gasification is shipped to Canada where it is injected into the ground to aid in oil recovery. Supporters acknowledge that economics can be problematic for carbon sequestration.