03 Energy and the Energy Transition
Learn how energy sources are converted into useful services, how energy choices affect emissions and other impacts, and what a reliable, accessible, and fair transition to low-carbon energy involves.
Energy sources and services
Energy systems provide services such as heating, mobility, lighting, manufacturing, and communication. comes directly from sources such as coal, sunlight, wind, or uranium. , including electricity and hydrogen, is made by converting .
Conversion and delivery can lose energy, so a country's electricity use is not the same as its total energy use. For example, petroleum is used mainly for transport, while electricity comes from a mix of energy sources. Energy use depends both on how much service people need and on how much energy is required to provide it. A well-insulated home needs less energy to stay warm than a drafty home of the same size.
and their effects
—coal, petroleum, and natural gas—formed from ancient organic matter. They are energy-dense, can be stored and burned when needed, and have powered electricity generation, transport, industry, and buildings.
Burning releases carbon dioxide (), a heat-trapping greenhouse gas. Extraction and transport can also release methane, while combustion produces air pollutants that harm health.
Long-lived fossil-fuel infrastructure, including power plants, pipelines, and industrial equipment, may continue operating for decades and thereby lock in emissions. Reducing energy-related emissions requires both cleaner energy supply and changes in how energy is used.
Renewable and other low-carbon energy
comes from sources replenished on human timescales, including solar, wind, hydropower, geothermal energy, and bioenergy. Sunlight and wind generate electricity without fuel combustion, but their output varies with weather and time of day. Hydropower can often be adjusted to meet demand, although dams can affect rivers and ecosystems.
Bioenergy can be renewable when biomass is regrown sustainably, but its land use, air pollution, and lifecycle emissions also matter. More broadly, is not impact-free: equipment requires materials, and projects can affect land, wildlife, and communities. Careful siting, recycling, and lifecycle assessment help identify and reduce these effects.
Nuclear power is not renewable, but it is another low-carbon electricity source because it generates power with very low operational carbon dioxide emissions. A high-renewable electricity system can combine different sources with transmission between regions, energy storage, flexible demand, and other reliable low-carbon generation. Batteries can shift electricity from sunny or windy periods to times of higher demand; they store energy rather than produce it.
Efficiency and
means providing the same service with less energy. Examples include efficient motors, LED lighting, better insulation, and heat pumps. A heat pump transfers heat rather than generating it through combustion or resistance, so it can provide more heating energy than the electricity it consumes. Efficiency can lower bills, reduce fuel use, and make it easier to meet demand with low-carbon energy supply.
replaces direct fuel use with electricity. Examples include using an electric vehicle instead of a gasoline-powered car and a heat pump instead of a gas furnace. The climate benefit of grows as the electricity supply becomes cleaner.
Some industrial processes, aviation, and shipping are harder to electrify. Low-emission hydrogen, sustainable biofuels, or other fuels may help in these applications.
Planning the
An is a system-wide shift in energy sources, technologies, infrastructure, and patterns of use. It involves building clean electricity generation and grids, improving efficiency, electrifying suitable uses, and reducing reliance on unabated .
Planning must maintain reliable service, expand energy access, and address affordability and impacts on workers and communities. The best combination of technologies varies by region, resources, infrastructure, and social priorities. A transition can reduce emissions by combining renewables and other low-carbon sources with efficiency, , storage, and stronger grids, while attending to reliability, access, and fairness.