Buildings and built environment
The Global Alliance for Buildings and construction (established at COP21) states that buildings and construction sector is responsible for 30% of global CO2 emissions. This figure is growing rapidly and could reach 50% of CO2 emissions by 2050. 
In these 30 to 50%, one considers the CO2 emissions related to the construction and the operation of the built environment. In a recent analysis done by Bajželj et al. in 2013 (2013), one can clearly identify the share of GHG emissions depending on the different industrial sectors and related services (figure 1).One can see that the emissions related to the construction service are very comparable to those related to the warmth service for buildings.
Figure 2: Sankey diagram of greenhouse gas emissions of human activities in 2010 related to the chain of technologies and systems required to deliver final services (Sce: ).
Actually, we could consider that around 40% of the total anthropogenic emissions are related to the built environment and that within these 40%, we include the construction of the buildings and their heating/cooling. For the moment, the share between operation and construction is about 60/40.
A reduction in these emissions implies a drastic change in the built environment, from the way we operate our buildings to the way we build them. The transition is slowly occurring, at small scale in industrialized countries, where retrofittedand new buildings are aiming toward a 0-energy standard (0-fossil energy operated buildings). However, this transition in the operation of buildings implies the remaining budget is dedicated to produce the materials for this operation. Otherwise it’s only shifting the impacts from one resource to another, filling one hole with other . . This aspect of a totally 0 fossil building (operation and construction) is much seldom considered.
Taking the Paris agreement seriously is the huge task for all due to the scale of changes that are required and the incredible limited amount of time we have to achieve this transition, instead of facing hard and unexpected changes, causing large scale migration, increasing droughts, fires, starvation, etc…Furthermore, as long as people are able to move, the built environment doesn’t which means that climate change will hit the built environment with very few possibilities to adapt to it or to flee.
The built environment at the world scale is quite a diverse agglomeration resulting from different living standard (influencing for instance the m2 per capita), climatic conditions (influencing heating/cooling demand) and construction practices (influencing the materials used and the building typology). The figure 3 shows an indication of the amount of people per construction type, and a indication of the embodied energy consequences of choosing a different materialisation.
Figure 3: Living condition of human population in the built environment. Share of the different type of construction and their associated embodied energy.
Some operate without or with hardly any operational energy, mostly in more warm climates, and with low income families. Some with very high GHG emissions, in colder or hot climates and by the more wealthy part of population ( wealthy in terms of money) . The major contribution therefore has to come from the housing and building sector in the industrialized and wealthy countries. Though the general trends towards 0-CO2 will remain the same everywhere.
People’s houses and stuff , left USA countryside, right China countryside. 
11 Bajželj B., Allwood J.M., Cullen J.M. 2013. Designing Climate Change Mitigation Plans That Add Up.Environmental Science & Technology, 47, 8062 – 8069.
12Rovers R., Beyond 0-energy: paradigm shift in assessment, in Buildings, special issue low Carbon Building design, 2015 Volume 5 page 1-13 , http://www.mdpi.com/2075-5309/5/1/1
13Material World: A Global Family Portrait Paperback – October 3, 1995 , Peter Menzel. More pictures have been collected later, see more pics from China: http://www.chinasmack.com/2011/pictures/family-possessions-living-environments-of-chinese-families.html