Wherever you turn, the topic of carbon and greenhouse gas emissions seems to be front and center. A growing number of publicly traded companies, governments, universities, and public interest groups have made reducing their carbon output a top priority. Some of these entities even have business models that are predicated on the release of large quantities of CO2 and a host of other greenhouse gasses into our atmosphere (hello, ExxonMobil), and happen to be very effective at communicating their reduction efforts. On that front, the topic of “greenwashing” is an altogether different subject worth exploring at another time, but it’s always good to keep in mind when any large corporation is addressing efforts to reduce their carbon emissions.

But what does it mean when someone attributes their actions to carbon emissions? If a corporation claims to be curbing their emissions, is it simply burning less fossil fuel as part of its business? It turns out it’s much more complicated than that.

The subject at hand concerns the nature of carbon emissions and the different types and categories they fall under. Much like ecosystems are intrinsically connected to the carbon cycle, emissions apply to building lifecycles – from material sourcing and construction to normal operations and end of life – and not just what gets emitted once the building is occupied and operational. This is what’s known as “whole life” carbon, and within that complex order are two main types of emissions: operational and embodied.

Operational vs. Embodied Carbon Emissions

Operational carbon represents the emissions that are the result of ongoing building operations, including lighting, power, water heating, ventilation, air conditioning, appliance use, and other day to day building needs. When people discuss efforts to reduce emissions, they are typically referring to interventions and adjustments aimed at curbing operational carbon.

Embodied carbon is a bit more complicated. This represents the CO2 emitted as a result of a building’s production. This includes the extraction, manufacturing, transportation, and installation of building materials, such as concrete, steel, lumber, insulation, and other key materials. Reducing embodied carbon often requires making large adjustments to material sourcing practices and the materials themselves, as well as design and construction schedules, building commissioning, and waste disposal procedures. Embodied carbon stems from many sources throughout a building’s lifecycle and is thus more difficult to measure (and reduce) when compared to operational energy use.

So, how does all this apply to the typical homeowner who is looking to lower their carbon footprint? From a building performance standpoint, one can reduce their home’s operational, day-to-day emissions using several measures, and it all starts with increasing efficiency. Installing and/or investing in renewable energy sources (solar and wind), purchasing Renewable Energy Certificates (REC’s), replacing fossil-fuel burning HVAC systems with all-electric air-source heat pumps, switching out incandescent bulbs for LED’s, installing high-performance windows, and switching out gas stoves for electric or induction ones are among some of the ways for homeowners to reduce their operational emissions.

Reducing one’s embodied emissions comes down to lifestyle choices, some of which can run counter to some of the recommendations listed in the previous paragraph. For instance, rather than purchase new, high-efficiency appliances like dishwashers and washing machines, repairing the older equipment is often the better choice. (In most cases, the energy consumed by older models more than offsets the energy needed – and resulting emissions – to dispose of them in place of new appliances.) Retrofitting, reusing, and salvaging are all more desirable choices, from an embodied carbon standpoint, when compared to tearing down and rebuilding with virgin building materials.

For any homeowners interested in measuring their carbon footprint, the EPA provides a useful calculator tool. This figure will account for your home’s energy usage, home heating and cooling, the gasoline burned from daily vehicle trips, and related activities.

If you’re looking for a deeper understanding of how greenhouse gas emissions are broken down by category in terms of direct and indirect actions, then it will serve you well to know the difference between Scope 1, 2, and 3 emissions.

Scope 1, 2, and 3 Emissions

Scope 1, 2, and 3 emissions comprise a series of boundaries within which most businesses operate. These scopes were originally developed at the turn of the 21^st century to help clarify where certain types of emissions come from, as well as how to measure and manage them. More than two decades on, we have a good handle on how to measure and manage scopes 1 and 2; far less so with 3.

Scope 1 emissions represents those greenhouse gases that are released as a direct result of normal business operations. By that logic, operational and scope 1 emissions are (almost) one and the same. Scope 2 represents the indirect emissions associated with the generation and consumption of purchased energy. Whenever an organization or business entity uses that energy to power buildings, vehicles, industrial equipment, or otherwise, that results in scope 2 emissions. Many multinational companies will regularly include data related to their scope 1 and 2 emissions in their annual reports.

Scope 3 is the leftovers. This represents all remaining indirect emissions that don’t fall under scope 2, including all upstream and downstream activities associated with operating a business. Upstream includes things like business travel, employee commutes, operational waste, and purchased goods and services. Downstream includes things like transportation and distribution of goods, the use of sold products, the end-of-life treatment of sold products, investments, and leased assets, among others. Simply by looking at such a list can one grasp how difficult it can be to accurately measure all those emissions sources.

Scope 4 Emissions?

There is a growing effort among business and public interests and the global climate advocacy community to formalize a reporting standard for measuring a new kind of emissions category. Scope 4 represents, broadly speaking, “avoided carbon emissions.” This doesn’t suggest emissions that don’t occur through inaction, but the avoided emissions that are directly tied to the use of certain efficient products, like low flow washing machines, heat pumps, and teleconferencing services that are used by employees who work from home.

Much like scope 3, measuring scope 4 emissions across any organization’s web of operations and practices and production cycles is a tricky proposition, to say the least. But the mere notion that “avoided emissions” is something worth tracking speaks to a growing awareness for better stewardship among all global citizens. It addresses, even implicitly, what kinds of actions people can take to improve their footprint, rather than simply reduce it.