Executive Summary

Buildings are key to a sustainable future because their design, construction, operation, and the activities in buildings are significant contributors to energy-related sustainability challenges – reducing energy demand in buildings can play one of the most important roles in solving these challenges. More specifically:

• The buildings sector and people's activities in buildings are responsible for approximately 31% of global final energy demand, approximately one-third of energy-related CO2 emissions, approximately two-thirds of halocarbon, and approximately 25–33% of black carbon emissions.

• Several energy-related problems affecting human health and productivity take place in buildings, including mortality and morbidity due to poor indoor air quality or inadequate indoor temperatures. Therefore, improving buildings and their equipment offers one of the entry points to addressing these challenges.

• More efficient energy and material use, as well as sustainable energy supply in buildings, are critical to tackling the sustainability-related challenges outlined in the GEA. Recent major advances in building design, know-how, technology, and policy have made it possible for global building energy use to decline significantly. A number of lowenergy and passive buildings, both retrofitted and newly constructed, already exist, demonstrating that low level of building energy performance is achievable. With the application of on-site and community-scale renewable energy sources, several buildings and communities could become zero-net-energy users and zero-greenhouse gas (GHG) emitters, or net energy suppliers.

Recent advances in materials and know-how make new buildings that use 10–40% of the final heating and cooling energy of conventional new buildings cost-effective in all world regions and climate zones.

Abstract

We place box models within the hierarchy of terrestrial biosphere models used to assess atmosphere–biosphere carbon fluxes, develop the mathematical formulation of biosphere box models, and examine how gross and net fluxes resulting from land-use changes and CO2 and temperature feedbacks can be separately and simultaneously incorporated into box models. We then summarize insights gained from sensitivity studies using a globally aggregated biosphere model, and close with a proposal for combining the box model approach with some of the simpler regionally disaggregated process models.

Introduction

Balancing the carbon cycle at the global scale requires that one account for the observed cumulative and year-to-year buildup in the amount of atmospheric CO2 as the difference between emissions of CO2 and its uptake by various sinks. It is widely assumed that the natural carbon cycle was sufficiently close to steady state prior to human influence that emissions were exactly balanced by removal processes. Hence, the task of balancing the carbon budget for the time interval since the beginning of human influence requires deriving estimates of the human-induced perturbation in both emission and sink terms such that the difference between total emission perturbations and total sink perturbations equals the observed buildup.