How To Reach U.S. Net Zero Emissions By 2050: Decarbonizing Buildings
- Dec 23, 2019 12:00 am GMT
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Presidential candidates, state governments, and utilities are promoting “net zero” emissions targets to rapidly reduce greenhouse gas (GHG) emissions and preserve a safe climate future by helping to limit global warming to well below 2°C. But few of them are exploring exactly how the U.S. could achieve the ambitious goal of remaking its energy economy.
Energy Innovation previously modeled a scenario to achieve the U.S. Paris Agreement pledge using the peer-reviewed, free, and open-source Energy Policy Simulator (EPS); it now uses the EPS to explore an illustrative policy package to achieve U.S. net zero emissions. By 2050, the net zero pathway abates more than 6 Gt of emissions a year and saves more than 120,000 American lives per year due to reduced particulate pollution.
This article focusing on the buildings sector is part two in a series of four identifying policy combinations that can achieve net zero U.S. GHG emissions by 2050. Other articles in the series cover the industry, electricity, and transportation sectors. (While emissions reductions from land use and agriculture represent roughly a tenth of those needed to reach net zero emissions, this series does not focus on that sector.)
The Paris Agreement targets net zero emissions by 2050. More than 60 countries, including Germany and the United Kingdom, have set net zero by 2050 goals, showing that political momentum can spur climate action – if the policy path forward is clear.
Emissions and energy use in today’s buildings
Buildings are responsible for 27% of U.S. emissions, or 8% if emissions from generating power are counted in the electricity sector (Figure 1).
Figure 1: U.S. GHG Emissions by Sector in 2018, with electricity sector emissions assigned to demand ... [+]
Under business-as-usual without policy intervention, emissions from buildings are expected to remain relatively constant through 2050, a trajectory incompatible with Paris Agreement goals. Fortunately, transforming how we provide energy for our buildings can help meet a net zero target by mid-century while providing Americans with clean air and lower energy bills in their living and working spaces.
Today, total building energy use is evenly split between commercial buildings (45% of demand), urban residential buildings (44%), and rural residential buildings (11%). Heating is the largest source of energy demand at 40% of all energy used in buildings, although appliances and other components also constitute large shares (Figure 2).
Figure 2: 2019 U.S. energy use in residential and commercial buildings, by component and building ... [+]
About 47% of energy consumed is buildings is provided by electricity, followed closely by natural gas at 41%. Remaining energy use comes from other petroleum products, biomass, and district heat (a centralized energy source that provides heat to multiple buildings).
In a business-as-usual scenario, electricity use is projected to remain relatively flat, but increase slightly through 2050, while natural gas holds relatively steady (Figure 3). But continuing to rely on natural gas in our buildings locks in decades of emissions, leaky infrastructure, and public health risks from poor indoor air quality.
Figure 3: U.S. energy use in buildings, by fuel type, in a business-as-usual pathway. Data from the ... [+]
Policies to decarbonize U.S. buildings
Various approaches can decarbonize buildings, but the most cost-effective and technologically feasible option is increasing the share of electric building components. However, decarbonizing buildings is challenging because building components take decades to turn over. For example, heaters – the largest source of building energy demand – last nearly 20 years, meaning a natural gas heater installed today will continue emitting GHGs until about 2040.
This means the longer we wait to electrify building components, the longer it takes to cut building emissions, which makes early targets key to reaching net zero emissions by mid-century. Electric building components can already be cheaper than natural gas equipment over component lifetimes, but up-front costs are still higher, requiring smart policy to accelerate the adoption of all-electric equipment.
In the net zero policy pathway, an ambitious sales mandate requiring all-electric new equipment and appliance standards by 2035 drives the overwhelming majority of emissions reductions in buildings – a cumulative 8100 million metric tons of carbon dioxide equivalent (Mt CO2e) between 2020 and 2050 (Figure 4). Policy requiring new construction to be all-electric should be enacted as soon as possible to accelerate the process.
Figure 4: Policies’ contribution to abatement of direct U.S. buildings’ emissions in the net zero ... [+]
Forward-thinking cities are already heading down that path. Berkeley, California led the way with its ban on natural gas pipes in many new buildings starting January 1, 2020 and other local governments in California, including San Francisco and Marin County, have adopted or are considering building electrification ordinances.
States like Massachusetts and Maine are also implementing policies to accelerate building electrification and reduce natural gas consumption in buildings. This trend could accelerate as more and more states and cities set 100% clean electricity targets, which is at odds with continued natural gas pipeline expansion.
Federal actions like midstream and upstream cash rebates (i.e., paid to installers, contractors, and distributors) for installing water and space heat pumps and induction cooktops, refundable tax credits, and low-cost financing for electrified building components could also help speed the transition.
Retrofits are another important way to accelerate building stock turnover by increasing the efficiency of existing buildings. Most of the buildings that will still be standing in 2050 have already been built – but high costs dissuade owners from making efficiency upgrades that carry significant GHG abatement potential.
A program offering financial incentives for retrofits, ideally targeting between 1% to 2% percent of U.S. homes and commercial buildings per year, is an ambitious but reasonable goal in line with targets in global building efficiency leader Germany. In the net zero policy pathway, retrofitting roughly 1% of homes and 1.5% of commercial buildings each year abates a cumulative 850 Mt CO2e.
Improving new building and equipment efficiency is the last critical piece to building decarbonization. The net zero policy pathway includes ambitious efficiency improvements for building envelopes (i.e., foundation, walls, roof) as well as all new equipment and appliances by 2050 – anywhere from 11% to 40% depending on the component. Together, these efficiency gains abate a cumulative 250 Mt CO2e.
Abatement from efficiency standards may seem low here because buildings transition to 100% clean electricity by 2050 in this scenario. Efficiency standards will drive greater GHG reductions if buildings fail to meet this ambitious target, and even if the target is reached, efficiency standards lower overall costs by reducing the amount of electricity generation capacity that must be built by 2050.
A few strong policies could spur dramatic building efficiency improvements, starting with a federal green building code. While many jurisdictions already use model codes (building codes written and maintained by expert standard-setting bodies), the U.S. could go further by establishing its own, continuously improving “green” model code incorporating both efficiency and low-carbon building materials.
A green building code should also be complemented by bolstering federal appliance standards to ensure homes and businesses benefit from the most efficient equipment. States and cities should also be encouraged to set their own stronger building codes, and training builders and inspectors in best practices helps ensure all codes are appropriately implemented.
Driving buildings to net zero emissions
Together, these policies could almost completely decarbonize U.S. buildings. Through 2050, building electrification would be responsible for 87% of the sector’s cumulative emissions reductions. Retrofits at the rate modeled here would drive nearly 10% of mitigation, with efficiency upgrades contributing an additional 3%.
Electrifying American buildings drastically cuts their energy use and eliminates natural gas use in buildings, which is the primary driver of direct emissions. Because electric components are 65% - 70% more efficient than natural gas equipment, efficiency gains from building code and appliance standards would cut overall energy use nearly 50% while maintaining the same level of comfort and service in America’s buildings (Figure 5).
Figure 5: U.S. energy use in buildings, by fuel type, in the net zero policy pathway. Data from the ... [+]
The net zero policy pathway’s ambitious efficiency policies limit electricity demand increases to roughly equivalent with electricity demand increase in business-as-usual (even with full building electrification), obviating the need for new electricity generation, saving money on power plant construction.
Early action is the key to building decarbonization
Fast action on building sector decarbonization, both for new and existing buildings, is key to net zero emissions by 2050. Because building components last for decades, a rapid shift to all-electric equipment sales will ensure the U.S. electrifies its buildings at the necessary rate.
Building efficiency retrofits, along with strong building codes and appliance standards, round out a building decarbonization strategy by curbing energy use and improving cost-effectiveness of the net zero pathway.