Powering buildings accounts for 26% of all global energy-related carbon emissions, making it one of the single largest contributors to climate change. That figure covers everything from the natural gas burned in furnaces and water heaters to the electricity drawn from the grid for lighting, cooling, and appliances. When you add in the emissions from constructing buildings in the first place, the share rises to more than one-third of global energy-related emissions, according to the International Energy Agency.
Where Building Emissions Come From
Building emissions fall into two categories. About 8% of global energy-related emissions come directly from burning fossil fuels inside buildings: gas furnaces, gas water heaters, gas stoves, and oil-fired boilers. The remaining 18% are indirect, produced at power plants that generate the electricity and district heating buildings consume. In other words, for every unit of carbon released by a gas furnace in someone’s basement, roughly two more units are released at a distant power plant to keep the lights and air conditioning running.
In U.S. commercial buildings, space heating alone consumed about 32% of total energy use as of 2018. Lighting and ventilation each accounted for roughly 10%. Residential buildings follow a similar pattern, with heating and cooling dominating energy budgets. This means the climate impact of any individual building depends heavily on two things: how it stays warm (or cool) and where its electricity comes from.
The Heating Problem
Natural gas is the dominant heating fuel in much of North America, Europe, and parts of Asia. Burning it produces CO2 directly inside the building, but the climate cost doesn’t stop there. Gas appliances also leak small amounts of methane, a greenhouse gas roughly 80 times more potent than CO2 over a 20-year window. Measurements of residential gas boilers in Beijing found average methane leakage rates of 0.22% during operation, with individual units ranging from nearly zero to almost 1%. Gas water heaters leak more (0.39% to 0.93%), and gas cooking appliances leak the most (0.8% to 1.3%). These percentages sound tiny, but methane’s potency means even small leaks add meaningful warming on top of the CO2 from combustion.
Switching from gas furnaces to electric heat pumps is one of the most effective ways to cut building emissions. Heat pumps move heat rather than generating it by burning fuel, making them two to four times more efficient. Research from the National Renewable Energy Laboratory found that heat pumps lower household emissions by 36% to 64% on average, cutting 2.5 to 4.4 metric tons of CO2 equivalent per home per year. Even in states with coal-heavy electrical grids, the efficiency advantage means heat pumps still reduce emissions by at least 13% compared to gas furnaces. In states with cleaner grids, the reduction reaches 72% in the first year alone.
The Cooling Feedback Loop
Air conditioning creates a less obvious but increasingly serious climate problem. AC systems work by pulling heat out of indoor air and dumping it outside. In dense cities, that waste heat raises outdoor temperatures, intensifying the urban heat island effect. Measurements have shown AC waste heat increasing nighttime air temperatures by more than 1°C in some urban areas. Warmer outdoor air then forces AC systems to work harder, consuming more electricity, which releases more waste heat. This positive feedback loop means that in semiarid cities during extreme heat events, cooling can consume more than 50% of total electricity demand, peaking at 65% during late afternoon hours.
The refrigerants circulating inside these AC systems carry their own climate risk. The most common refrigerant in residential and commercial systems, R-410A, has a global warming potential of 2,088. That means one kilogram of R-410A leaked into the atmosphere traps as much heat as 2,088 kilograms of CO2. Leaks happen during installation, maintenance, and disposal. Global regulations are now phasing down these high-impact refrigerants, but the transition will take years to fully reach existing equipment.
How Grid Electricity Multiplies the Impact
The climate footprint of any electric building depends on what fuel mix generates its electricity. A home running on hydropower or solar has near-zero indirect emissions. The same home connected to a coal-heavy grid could produce more emissions from its electricity use than a comparable gas-heated home saves by avoiding on-site combustion. This is why grid decarbonization and building electrification work as a pair. Modeling by NREL explored scenarios ranging from aggressive decarbonization (95% carbon-free electricity by 2035) to sluggish progress (only 50% by 2035). In every scenario, electrified buildings performed better than gas-powered ones, but the gap widened dramatically as the grid got cleaner.
This relationship also explains why energy efficiency in buildings matters so much. Every kilowatt-hour you don’t use is a kilowatt-hour that doesn’t need to be generated, transmitted, or paid for. Better insulation, LED lighting, smart thermostats, and efficient appliances all shrink a building’s demand on the grid. Reducing demand is especially valuable during peak hours, when utilities often fire up their dirtiest, least efficient power plants to meet surges in cooling or heating load.
What a Lower-Carbon Building Looks Like
The IEA’s net-zero roadmap calls for all new buildings to be “zero-carbon ready” by 2025, meaning they are designed to run entirely on clean energy without structural retrofits. The roadmap also calls for no new sales of fossil fuel boilers starting in 2025, with electric heat pumps replacing them globally. These targets are ambitious, and most countries are not on track to meet them, but they outline what the building sector needs to look like if the world is serious about limiting warming.
For existing buildings, the path is more gradual. Retrofitting insulation, replacing gas equipment at end of life with heat pumps, upgrading to efficient windows, and installing rooftop solar all chip away at a building’s emissions profile. A single-family home in Colorado that swaps a gas furnace for a heat pump can eliminate roughly 6 metric tons of CO2 per year. Multiply that across millions of homes and commercial buildings, and the building sector shifts from being one of the largest sources of emissions to one of the most tractable problems in climate policy.
The core dynamic is straightforward: buildings use enormous amounts of energy, much of it generated by burning fossil fuels either on-site or at power plants. Every improvement in efficiency, every fuel switch from gas to electric, and every increment of clean energy added to the grid chips away at that 26% share of global emissions. The technology to do this exists today. The challenge is deploying it fast enough and widely enough to matter.