Series: Measuring the Elements of Climate Change
Discussions of climate change often refer to phenomena such as global warming and increased greenhouse gas emissions. Ever wonder how we measure such things? How do we know that the global temperature has increased? How do we measure greenhouse gas amounts? What about decarbonization, tree canopies, auto and truck emissions, sea-level rise, glacier melting, and environmental justice?
In this series, we will learn how climate change indicators are measured and how they change over time. The reliable and ongoing measurement of these conditions is essential for monitoring climate change and promoting climate action.
Part 3: Decarbonization of Buildings
An astonishing two-thirds of New York City’s carbon emissions come from the fossil fuels used to heat, cool, and power buildings. In New York State, emissions from all building types account for about one-third of all GHG emissions. New York City and New York State have taken slightly different approaches to limiting and eliminating these emissions, reflecting the types and distribution of buildings and the ways the problem can be addressed.
The City has enacted Local Law 97 (LL97) to establish limits on and strategies to reduce building emissions for a defined subset of all buildings in the city. The job is, nevertheless, enormous. New York City has roughly 700,000 buildings that consume energy in various ways and emit GHG in equally complicated ways and amounts. LL 97 applies only to buildings with more than 25,000 sq ft. There are close to 50,000 such buildings in this category, and they collectively account for about 50 percent of building GHG emissions in New York City. They represent a consequential target for GHG reduction.
For New York City’s LL97 strategy, GHG building emissions are easy to calculate: count usage of all types of energy consumed by a building, multiply that number by a coefficient that represents GHG emissions by fuel source, and add those together. On the other hand, measurements need to account for property type (multifamily, office, hotel, store, condominium, data center, etc.), affordable and income-restricted housing, and specific categories of exemption to set limits and timetables for reduction. The calculation, however, is the same: energy used times a fuel-specific factor.
Individual building energy consumption is computed using available annual energy use data and building use factors (coefficients) developed by the EPA Energy Star Portfolio Manager (ESPM) system.
There is little controversy about the measurement of building emissions. The number for each building is not exact, but it is easy to compute and will always be close to the actual energy use and GHG emissions. Buildings are required to submit annual usage reports that the New York City Department of Buildings reviews. LL97 phases in carbon caps and the limits become more stringent over a series of compliance periods of about five years each between 2024 and 2049. Limits vary by property type, but all ratchet down carbon emissions over time.
Because there is no controversy about measurement, it is possible to set interim goals for reduction, and there are available means to accomplish them. Emission goals can be achieved by retrofitting heating and cooling systems with new, more efficient electric equipment, sealing buildings, and conserving energy.
The costs of achieving reductions are spread over a sufficiently long period. Government measures support them, so planners are confident that carbon emissions from buildings in NYC will follow the anticipated downward trajectory, with a substantial impact on local GHG conditions. Good measurement can lead to good climate action.
New York State has taken a slightly different approach to decarbonizing buildings. On one hand, it uses a broader definition of carbon emissions by buildings, including single-family homes, for example, than the NYC approach. Still, it is less prescriptive about decarbonization goals. Decarbonization of buildings in New York State encompasses all 6 million buildings, from garages to single-family homes to skyscrapers. It views building emissions as part of an ecosystem of carbon emissions. As a result, the regulatory and financial approaches to reducing building contributions to GHG emissions differ slightly from the New York City approach, which directly targets larger buildings.
Building decarbonization at the state level considers emissions in the broader context of energy sources and state energy infrastructure. Regulation of GHG emissions from buildings seeks to minimize energy consumption, decarbonize all possible end uses, enable a building to shift or offset energy loads, and utilize the cleanest mix of energy resources.
New York regulatory actions are also based on a suite of metrics rather than a single GHG metric, providing the accuracy and flexibility needed for the State’s shift toward carbon-neutral buildings.
For example, decarbonizing an existing building is more challenging and more expensive than achieving carbon-neutral performance in new construction. This is because retrofits must consider impacts and disruptions to current occupants, often require costly upgrades to modernize the building, such as environmental remediation or electrical system upgrades, and are generally constrained by the building’s existing system configurations.
As a result, the sources and amounts of GHG emissions from existing structures are likely larger than those from new, energy-efficient construction. They are certainly more difficult to offset or reduce.
New York State’s response to building-related GHG emissions addresses single-family home emissions, as well as commercial structures and “embedded” structural emissions like emissions related to building material components and construction-related energy use that the New York City LL 97 does not. The State has specified new construction energy standards. For New York State, the strategy is to retrofit existing heating, cooling, and water-heating systems that rely on fossil fuels with systems that use renewable sources, are efficient, and include structural upgrades such as improved household insulation (building envelopes). It also relies on new construction to replace energy-inefficient, fossil fuel-utilizing structures. Retrofitting, improving energy efficiency, and new construction will automatically reduce GHG emissions without requiring measurement of individual building emissions. (Overall building emissions are, in fact, calculated by multiplying fuel use by CO2e (CO2 equivalents)- as New York City does- and such calculations are used to estimate the State’s energy utilization year over year, for example.) The State provides financial, technical support and regulation to achieve this goal. Some of that support is available to homeowners, and some is invested in upgrading the electrical grid and other infrastructure. The problem is understood to be both systemic and individual (single homes, multiple dwellings and commercial).
The approaches to building decarbonization by the state and the city are not contradictory. They are complementary, differing in scope and measurement. They underscore the relationships between scope, legal requirements and remediation strategy. But the long-term goal of each is to reduce GHG emissions from this substantial source.