In 2004, emissions from the buildings sector including through electricity use were about 8.6 GtCO2, 0.1 GtCO2-eq N2O, 0.4 GtCO2-eq CH4 and 1.5 GtCO2-eq halocarbons (including CFCs and HCFCs). Using an accounting system that attributes CO2 emissions to electricity supply rather than buildings end-uses, the direct energy-related carbon dioxide emissions of the building sector are about 3 Gt/yr.
For the buildings sector the literature uses a variety of baselines. Therefore a baseline was derived for this sector based on the literature, resulting in emissions between the B2 and A1B SRES scenarios, with 11.1 Gt of emissions of CO2 in 2020 and 14.3 GtCO2 in 2030 (including electricity emissions but omitting halocarbons, which could conceivably be substantially phased out by 2030).
Measures to reduce greenhouse gas (GHG) emissions from buildings fall into one of three categories: reducing energy consumption and embodied energy in buildings, switching to low-carbon fuels including a higher share of renewable energy, or controlling the emissions of non-CO2 GHG gases. This chapter devotes most attention to improving energy efficiency in new and existing buildings, which encompasses the most diverse, largest and most cost-effective mitigation opportunities in buildings.
The key conclusion of the chapter is that substantial reductions in CO2 emissions from energy use in buildings can be achieved over the coming years using mature technologies for energy efficiency that already exist widely and that have been successfully used (high agreement, much evidence).