As stated in The Energy Manifesto, energy accounts for more than its fair share of greenhouse gas emissions, so it's of paramount importance in the grand scheme of tackling climate change. The answer of course is a massive shift to renewable energy, but I'm fairly certain when I wake up tomorrow morning we will be nowhere near to meeting our energy demands from renewable sources. If, for now, dirty energy is a necessary evil, which sources should we be using? Let's take a look at our current sources of energy, grade them out, and answer the question.
Coal is the primary source of electricity worldwide. It is mined from the earth through both underground mining and mountaintop removal techniques. It is then transported to power plants where it is burned to create steam that powers turbines and generates electricity. When burned it releases carbon dioxide, sulfur dioxide, nitrogen oxides, and mercury compounds, none of which are earth-friendly. The refining process requires large amounts of water to remove impurities from the coal, which causes contamination of nearby bodies of water, affecting drinking water and wildlife habitat. "Clean coal" refers to a sequestration technique that supposedly captures undefined percentages of emissions from the power plant. But it is no perfect science and doesn't speak to the environmental problems caused by the mining process.
Grade: F (massive environmental harm through sourcing and energy generation)
Oil is primarily used for transportation and heating purposes, but is also used to create electricity. It is extracted from the earth by drilling deep wells and pumping it to the surface. Then it is transported to a refinery where it is turned into gasoline, kerosene, propane, jet fuels, and the like. Sometimes, oil is sent to power plants where it is burned to generate electricity. Burning oil produces nitrogen oxides, sulfur dioxide, carbon dioxide, methane, and mercury compounds. The engines used to drill, produce, and transport the oil also burn fuels that generate emissions. As we know from the Deepwater Horizon disaster, drilling spills can be catastrophic for the environment. Large quantities of water are used in power plants for steam production and cooling, and they release wastewater that pollute local bodies of water, thus harming wildlife and contaminating drinking water. They also produce solid toxic waste sludge that must be properly disposed or can be extremely hazardous.
Grade: F (potentially massive environmental harm through sourcing and massive environmental harm through energy generation)
Nuclear energy uses fission of the uranium atom to release energy that creates steam and subsequently electricity. Uranium, a non-renewable element, is mined from the earth and transported to processing plants where it is concentrated into enriched fuels that are suitable for fission. The fission process creates many radioactive by-products like tritium, cesium, krypton, neptunium, and iodine. The power plants do not emit carbon dioxide, sulfur dioxide, or nitrogen oxides, but the mining process does. Power plants use large quantities of water from local sources, and discharge the water after use often with small amounts of radioactive elements. After the uranium is used, radioactive materials are left behind and are stored in power plants in steel-lined concrete vaults that are often filled with water. Sometimes it gets shipped to disposal sites. If the radioactive materials are exposed, the results can be apocalyptic. Unless natural disasters stop happening forever and our storage containers of radioactive waste are never in jeopardy of being compromised, nuclear plants are always at risk of becoming the next Chernobyl or Fukishima.
Grade: F+ (some environmental harm through sourcing and potentially massive environmental harm through energy generation)
Natural gas is another fossil fuel that can be found in the earth's crust. Wells are drilled into the ground (or seafloor) to remove the gas. It is transported to gas plants to remove impurities, then sent via pipeline to power plants. Natural gas is burned in a variety of ways to create electricity, and produces much lower levels of nitrogen oxides and carbon dioxides than coal or oil. Some methane can be released, but sulfur dioxide and mercury compounds are negligible. Water pollution can take place from power plant discharges. Hydraulic fracturing or "fracking," another technique for extractment, involves shooting water and small amounts of chemicals at high pressures into the well to break the shale and release natural gas. This has been proven to cause drinking water pollution that is harmful to humans and wildlife.
Grade: C (Fracking = D) (potentially large environmental harm through sourcing and moderate environmental harm through energy creation)
Disclaimer: This is in no way an endorsement of natural gas. These grades are not for a perfect world, but the one we live in. If we have to choose, natural gas appears to be better for the planet than coal, oil, and nuclear energy. But all of these energy sources either contribute to climate change and/or put us at risk of a severe environmental catastrophe.
Photo: Mountaintop removal coal mining in the Appalachians. (J Henry Fair via NRDC)