How Does the Construction of a Residential Area Contribute to Climate Change? - Timing Reveals New Perspectives to Climate Change Mitigation

Climate change, driven by greenhouse gas (GHG) emissions, is considered to be one of the most severe threats to the mankind in the future. Consequently, various institutions have set climate change mitigation targets that require substantial GHG reductions throughout all industries. The real estate and construction sector is responsible for a significant share of the global GHG emissions and therefore is expected to contribute remarkably to climate change mitigation targets. The use phase emissions had been considered to dominate the building life cycle emissions until the modern energy-efficient housing types emerged. Since then, relative shares of construction and use phase emissions have changed and the construction phase actually seems to dominate the life cycle emissions of the modern housing types. The early timing of the construction phase emissions in a building life cycle raises their harmfulness. Yet, construction of new residential areas is expected to contribute positively to climate change mitigation due to improved energy efficiency that rapidly negates the construction phase emissions. The dissertation argues that the contribution of a residential area construction to climate change is wider than what the common belief is. The studies employ hybrid LCA models that are used in assessing construction and use phase GHG emissions. The analyses include a temporal perspective, which highlights the relevance of construction phase emissions i.e. a carbon spike occurring early compared to the use phase emissions emitted in the distant future. The main argument of the dissertation is that the construction phase carbon spike is likely to turn the new residential areas' expected benefits from high energy-efficiency into undesired acceleration of climate change. This is due to significant construction phase emissions remaining in the atmosphere for a long time and increasing the atmosphere's GHG concentration for several decades. Additionally, use phase emissions occurring in the distant future contain significant uncertainties that might reduce the anticipated benefits of new energy-efficient housing. The dissertation suggests that energy renovations of the current building stock should be favoured instead of new construction projects whenever possible. Thus, the energy efficiency of the current building stock increases with less construction phase emissions. While the issue was not investigated in this dissertation, finding and utilizing low-carbon materials in new constructions and thus reducing the carbon spike would also offer a solution. Only minimizing both the construction and use phase emissions will result in true low impact residential areas.