The Methodology Behind Decarbonize Your Life

There is no dearth of advice on the internet about how to lower your personal carbon emissions, but if we had found any of it completely satisfying, we wouldn’t have embarked on this project in the first place.

Our goal with Decarbonize Your Life is to draw your attention to two things — the relative emissions benefits of different actions, as well as the relative structural benefits. (You’ll find everything you need to know about the project here.) For the first, we needed some help. So we shared our vision with WattTime, a nonprofit that builds data-driven tools to help people, companies, and policymakers figure out how to reduce emissions, and lucky for us, they were excited to support the project.

“So many people out there feel helpless when it comes to addressing the climate crisis, but we believe that anyone, anywhere should have the tools and information they need to make a difference,” Henry Richardson, a senior analyst at WattTime, told me as we were wrapping up this project. “So we love the idea of helping average consumers understand which actions actually available to them can meaningfully contribute to reducing climate pollution. We want to help people prioritize those higher-impact activities that can mitigate climate change faster.”

WattTime’s claim to fame is building an API that calculates the emissions impact of using the grid at a given time and place. Users can then shift their energy consumption to times when the grid is cleaner or to build renewables in places where they will reduce emissions the most.

In an ideal world, we would have taken a similar time- and place-based approach in calculating the emissions savings of each energy-related action on our list. Switching to an EV if you live somewhere with very clean power will reduce emissions more than if you live somewhere with lots of coal plants, and likewise, getting rooftop solar if you live somewhere with coal-fired electricity is more effective than in areas with a cleaner grid. But when we started to game it out, we realized that level of exactitude would be, if not exactly impossible, certainly insanity-inducing.

Instead, WattTime helped us calculate the effect of each action if it was undertaken by an “average American household” — that is, one that consumes an average amount of electricity per year, drives an average number of miles in an average car per year, uses an average amount of energy for space heating, et cetera. WattTime also pulled data from publicly available sources like the Environmental Protection Agency, the Department of Energy, and the Energy Information Administration, to estimate the baseline emissions and savings of a given action. We ultimately made two calculations for each action to account for two different ways of estimating the emissions from using the electric grid:

• One that shows the emissions impact of using the electric grid today, based on WattTime’s data.

• One that shows the emissions impact of using the grid over the next several decades as it grows cleaner, based on Cambium, a dataset developed by the National Renewable Energy Lab.

While the first method gives us a picture of how much good each action can do in an immediate sense, the second gives us a picture of how much good it can do over time. For example, using the first method, buying clean power came out on top, with rooftop solar offering the potential to cut CO2 by about 5.7 metric tons per year, while switching to an electric vehicle would cut about 3 metric tons per year. But using the second method, car-related actions won out, showing EVs cutting CO2 by 4.6 metric tons per year, and rooftop solar cutting 1.4 metric tons per year. The truth is probably somewhere in the middle.

To calculate the emissions savings from dietary changes and food waste management, we turned to two more partners: HowGood, a data platform for food system lifecycle analysis, and ReFED, which collects similar data for food waste. As with energy, we used federal data from the U.S. Department of Agriculture to estimate the average American diet and ReFED’s estimates for the average American food waste mix (though note that those are for an individual, not for a household). From there, WattTime helped us determine that, for instance, just by replacing the beef in your diet with chicken, you could save nearly 2.5 metric tons of emissions each year — almost as much as you could save by going vegan.

Because we used averages and sought to simplify our list with actions like “electrify your space heating system,” rather than estimating the impact of every permutation like “switch from a propane furnace in Colorado with X efficiency to a cold climate heat pump with Y efficiency,” our estimates of emissions reductions are rough approximations and not reflective of real-world scenarios.

You’ll see that while these calculations certainly informed our ranking, they were not the sole metric we used to arrange this list. A quantitative analysis alone could not answer our question about the most “high-leverage” actions, so we used our reporting and expertise as climate journalists to fill in that last, crucial gap. Car-related actions and rooftop solar were neck-and-neck by the numbers, but we are confident that getting an EV (if you need to have a car) is more unambiguously necessary for the energy transition than getting rooftop solar. Similarly, while eating less meat can hugely reduce the carbon tied to an individual’s diet, the ripple effect it has on agricultural carbon emissions is less direct and harder to parse than the effect you can have by electrifying all your appliances and shutting down your natural gas account.

HEATMAP’S NUMBERS:

1. If you need a car, get an EV

Getting an EV:

WattTime — 2.9 mtCO2/yr
Cambium — 4.5 mtCO2/yr

Structural benefits: Destroying demand for oil; increasing demand for charging stations; improving local air quality and chipping away at the social license for operating an internal combustion engine.

2. Go zero-carbon power at home

Getting rooftop solar:

WattTime — 5.7 mtCO2/yr
Cambium — 1.4 mtCO2/yr

Structural benefits: Get clean energy on the grid faster than utility-scale projects; influence neighbors; reduce electric demand in your neighborhood; reduce strain on grid if paired with a battery and part of a “virtual power plant”

3. Give your home an energy efficient renovation

Air-sealing and insulation:

WattTime — 1.2 mtCO2/yr

Structural benefits: Reduce strain on grid and need for grid investment; level out electricity demand to avoid the need to activate dirty “peaker” gas plants; prepare your home for cheaper, more even, and efficient heating and cooling

4. Electrify your appliances

Switching to a heat pump for space heating:

WattTime — 1.4 mtCO2/yr
Cambium — 1.6 mtCO2/yr

Switching from a gas stove to an induction stove:

WattTime — Roughly even
Cambium — 0.1 mtCO/yr

Switching to a heat pump for water heating:

WattTime — 0.8 mtCO2/yr
Cambium — 1.6 mtCO2/yr

Switching from a natural gas-powered dryer to a heat pump dryer:

WattTime — Roughly even
Cambium — 0.1 mtCO/yr

Structural benefits: Increase demand for and reduce price of electric and efficient appliances; build a case for policies that wind down fossil fuel use; if fully electrifying, sends signal to downsize gas system.

5. Drive less, bike (or walk or scoot) more

Getting rid of your car:

WattTime — 5.17 mtCO/yr

Structural benefits: Supporting public transit and bike lanes, enabling others to use their cars less, too.

6. Eat less meat and reduce food waste

Switching from an omnivorous to a vegetarian diet:

WattTime and HowGood — 2.8 mtCO2/yr

Switching from an omnivorous to a vegan diet:

WattTime and HowGood — 2.9 mtCO2/yr

Replacing the beef in an omnivorous diet with chicken:

WattTime and HowGood — 2.5 mtCO2/yr

Structural benefits: Reduce demand for high-emitting food products, which has the double-pump benefit of reducing the amount of land required to cultivate high-emitting products; if replacing beef with chicken, increase demand for more carbon-efficient proteins; add to the business case for developing efficient plant-based proteins.

Cutting food waste in half:

WattTime and ReFED — more than 0.1 mtCO2/yr

Structural benefits: Reduce demand across the food system; send less food waste to landfill, which helps reduce methane emissions.

Composting all food waste:

WattTime and ReFED — 0.03 mtCO2/yr

Structural benefits: Encourages the build-out of municipal composting programs; encourages responsible farming practices by lowering the cost of compost; reduces demand for nitrogen-based fertilizer.